From 50fb4f7fc907efff65eadb0b74387a9ffed6e849 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:22 -0800 Subject: [PATCH 01/24] freezer: fix current->state restoration race in refrigerator() refrigerator() saves current->state before entering frozen state and restores it before returning using __set_current_state(); however, this is racy, for example, please consider the following sequence. set_current_state(TASK_INTERRUPTIBLE); try_to_freeze(); if (kthread_should_stop()) break; schedule(); If kthread_stop() races with ->state restoration, the restoration can restore ->state to TASK_INTERRUPTIBLE after kthread_stop() sets it to TASK_RUNNING but kthread_should_stop() may still see zero ->should_stop because there's no memory barrier between restoring TASK_INTERRUPTIBLE and kthread_should_stop() test. This isn't restricted to kthread_should_stop(). current->state is often used in memory barrier based synchronization and silently restoring it w/o mb breaks them. Use set_current_state() instead. Signed-off-by: Tejun Heo --- kernel/freezer.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/kernel/freezer.c b/kernel/freezer.c index 7be56c534397..3f460104a9d6 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -58,7 +58,13 @@ void refrigerator(void) current->flags &= ~PF_FREEZING; pr_debug("%s left refrigerator\n", current->comm); - __set_current_state(save); + + /* + * Restore saved task state before returning. The mb'd version + * needs to be used; otherwise, it might silently break + * synchronization which depends on ordered task state change. + */ + set_current_state(save); } EXPORT_SYMBOL(refrigerator); From 3a7cbd50f74907580eb47a8d08e1f29741b81abf Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:22 -0800 Subject: [PATCH 02/24] freezer: don't unnecessarily set PF_NOFREEZE explicitly Some drivers set PF_NOFREEZE in their kthread functions which is completely unnecessary and racy - some part of freezer code doesn't consider cases where PF_NOFREEZE is set asynchronous to freezer operations. In general, there's no reason to allow setting PF_NOFREEZE explicitly. Remove them and change the documentation to note that setting PF_NOFREEZE directly isn't allowed. -v2: Dropped change to twl4030-irq.c as it no longer uses PF_NOFREEZE. Signed-off-by: Tejun Heo Acked-by: "Gustavo F. Padovan" Acked-by: Samuel Ortiz Cc: Marcel Holtmann Cc: wwang --- Documentation/power/freezing-of-tasks.txt | 2 +- drivers/bluetooth/btmrvl_main.c | 2 -- drivers/mfd/twl6030-irq.c | 2 -- drivers/staging/rts_pstor/rtsx.c | 2 -- 4 files changed, 1 insertion(+), 7 deletions(-) diff --git a/Documentation/power/freezing-of-tasks.txt b/Documentation/power/freezing-of-tasks.txt index 316c2ba187f4..587e0828053f 100644 --- a/Documentation/power/freezing-of-tasks.txt +++ b/Documentation/power/freezing-of-tasks.txt @@ -67,7 +67,7 @@ III. Which kernel threads are freezable? Kernel threads are not freezable by default. However, a kernel thread may clear PF_NOFREEZE for itself by calling set_freezable() (the resetting of PF_NOFREEZE -directly is strongly discouraged). From this point it is regarded as freezable +directly is not allowed). From this point it is regarded as freezable and must call try_to_freeze() in a suitable place. IV. Why do we do that? diff --git a/drivers/bluetooth/btmrvl_main.c b/drivers/bluetooth/btmrvl_main.c index a88a78c86162..6c3defa50845 100644 --- a/drivers/bluetooth/btmrvl_main.c +++ b/drivers/bluetooth/btmrvl_main.c @@ -475,8 +475,6 @@ static int btmrvl_service_main_thread(void *data) init_waitqueue_entry(&wait, current); - current->flags |= PF_NOFREEZE; - for (;;) { add_wait_queue(&thread->wait_q, &wait); diff --git a/drivers/mfd/twl6030-irq.c b/drivers/mfd/twl6030-irq.c index 3eee45ffb096..c6b456ad7342 100644 --- a/drivers/mfd/twl6030-irq.c +++ b/drivers/mfd/twl6030-irq.c @@ -138,8 +138,6 @@ static int twl6030_irq_thread(void *data) static const unsigned max_i2c_errors = 100; int ret; - current->flags |= PF_NOFREEZE; - while (!kthread_should_stop()) { int i; union { diff --git a/drivers/staging/rts_pstor/rtsx.c b/drivers/staging/rts_pstor/rtsx.c index 480b0ed2e4de..8a7803cf88d2 100644 --- a/drivers/staging/rts_pstor/rtsx.c +++ b/drivers/staging/rts_pstor/rtsx.c @@ -466,8 +466,6 @@ static int rtsx_control_thread(void *__dev) struct rtsx_chip *chip = dev->chip; struct Scsi_Host *host = rtsx_to_host(dev); - current->flags |= PF_NOFREEZE; - for (;;) { if (wait_for_completion_interruptible(&dev->cmnd_ready)) break; From a0acae0e886d44bd5ce6d2f173c1ace0fcf0d9f6 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:22 -0800 Subject: [PATCH 03/24] freezer: unexport refrigerator() and update try_to_freeze() slightly There is no reason to export two functions for entering the refrigerator. Calling refrigerator() instead of try_to_freeze() doesn't save anything noticeable or removes any race condition. * Rename refrigerator() to __refrigerator() and make it return bool indicating whether it scheduled out for freezing. * Update try_to_freeze() to return bool and relay the return value of __refrigerator() if freezing(). * Convert all refrigerator() users to try_to_freeze(). * Update documentation accordingly. * While at it, add might_sleep() to try_to_freeze(). Signed-off-by: Tejun Heo Cc: Samuel Ortiz Cc: Chris Mason Cc: "Theodore Ts'o" Cc: Steven Whitehouse Cc: Andrew Morton Cc: Jan Kara Cc: KONISHI Ryusuke Cc: Christoph Hellwig --- Documentation/power/freezing-of-tasks.txt | 12 ++++++------ drivers/net/irda/stir4200.c | 2 +- fs/btrfs/async-thread.c | 2 +- fs/btrfs/disk-io.c | 8 ++------ fs/ext4/super.c | 3 +-- fs/gfs2/log.c | 4 ++-- fs/gfs2/quota.c | 4 ++-- fs/jbd/journal.c | 2 +- fs/jbd2/journal.c | 2 +- fs/jfs/jfs_logmgr.c | 2 +- fs/jfs/jfs_txnmgr.c | 4 ++-- fs/nilfs2/segment.c | 2 +- fs/xfs/xfs_buf.c | 2 +- include/linux/freezer.h | 17 ++++++++--------- kernel/freezer.c | 10 +++++++--- 15 files changed, 37 insertions(+), 39 deletions(-) diff --git a/Documentation/power/freezing-of-tasks.txt b/Documentation/power/freezing-of-tasks.txt index 587e0828053f..3ab9fbd2800a 100644 --- a/Documentation/power/freezing-of-tasks.txt +++ b/Documentation/power/freezing-of-tasks.txt @@ -21,7 +21,7 @@ freeze_processes() (defined in kernel/power/process.c) is called. It executes try_to_freeze_tasks() that sets TIF_FREEZE for all of the freezable tasks and either wakes them up, if they are kernel threads, or sends fake signals to them, if they are user space processes. A task that has TIF_FREEZE set, should react -to it by calling the function called refrigerator() (defined in +to it by calling the function called __refrigerator() (defined in kernel/freezer.c), which sets the task's PF_FROZEN flag, changes its state to TASK_UNINTERRUPTIBLE and makes it loop until PF_FROZEN is cleared for it. Then, we say that the task is 'frozen' and therefore the set of functions @@ -29,10 +29,10 @@ handling this mechanism is referred to as 'the freezer' (these functions are defined in kernel/power/process.c, kernel/freezer.c & include/linux/freezer.h). User space processes are generally frozen before kernel threads. -It is not recommended to call refrigerator() directly. Instead, it is -recommended to use the try_to_freeze() function (defined in -include/linux/freezer.h), that checks the task's TIF_FREEZE flag and makes the -task enter refrigerator() if the flag is set. +__refrigerator() must not be called directly. Instead, use the +try_to_freeze() function (defined in include/linux/freezer.h), that checks +the task's TIF_FREEZE flag and makes the task enter __refrigerator() if the +flag is set. For user space processes try_to_freeze() is called automatically from the signal-handling code, but the freezable kernel threads need to call it @@ -61,7 +61,7 @@ wait_event_freezable() and wait_event_freezable_timeout() macros. After the system memory state has been restored from a hibernation image and devices have been reinitialized, the function thaw_processes() is called in order to clear the PF_FROZEN flag for each frozen task. Then, the tasks that -have been frozen leave refrigerator() and continue running. +have been frozen leave __refrigerator() and continue running. III. Which kernel threads are freezable? diff --git a/drivers/net/irda/stir4200.c b/drivers/net/irda/stir4200.c index 41c96b3d8152..e880c79d7bd8 100644 --- a/drivers/net/irda/stir4200.c +++ b/drivers/net/irda/stir4200.c @@ -750,7 +750,7 @@ static int stir_transmit_thread(void *arg) write_reg(stir, REG_CTRL1, CTRL1_TXPWD|CTRL1_RXPWD); - refrigerator(); + try_to_freeze(); if (change_speed(stir, stir->speed)) break; diff --git a/fs/btrfs/async-thread.c b/fs/btrfs/async-thread.c index 7ec14097fef1..98ab240072e5 100644 --- a/fs/btrfs/async-thread.c +++ b/fs/btrfs/async-thread.c @@ -340,7 +340,7 @@ again: if (freezing(current)) { worker->working = 0; spin_unlock_irq(&worker->lock); - refrigerator(); + try_to_freeze(); } else { spin_unlock_irq(&worker->lock); if (!kthread_should_stop()) { diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c index 62afe5c5694e..622654fe051f 100644 --- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -1579,9 +1579,7 @@ static int cleaner_kthread(void *arg) btrfs_run_defrag_inodes(root->fs_info); } - if (freezing(current)) { - refrigerator(); - } else { + if (!try_to_freeze()) { set_current_state(TASK_INTERRUPTIBLE); if (!kthread_should_stop()) schedule(); @@ -1635,9 +1633,7 @@ sleep: wake_up_process(root->fs_info->cleaner_kthread); mutex_unlock(&root->fs_info->transaction_kthread_mutex); - if (freezing(current)) { - refrigerator(); - } else { + if (!try_to_freeze()) { set_current_state(TASK_INTERRUPTIBLE); if (!kthread_should_stop() && !btrfs_transaction_blocked(root->fs_info)) diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 9953d80145ad..877350ef0253 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -2882,8 +2882,7 @@ cont_thread: } mutex_unlock(&eli->li_list_mtx); - if (freezing(current)) - refrigerator(); + try_to_freeze(); cur = jiffies; if ((time_after_eq(cur, next_wakeup)) || diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c index 598646434362..8154d42e4647 100644 --- a/fs/gfs2/log.c +++ b/fs/gfs2/log.c @@ -951,8 +951,8 @@ int gfs2_logd(void *data) wake_up(&sdp->sd_log_waitq); t = gfs2_tune_get(sdp, gt_logd_secs) * HZ; - if (freezing(current)) - refrigerator(); + + try_to_freeze(); do { prepare_to_wait(&sdp->sd_logd_waitq, &wait, diff --git a/fs/gfs2/quota.c b/fs/gfs2/quota.c index 7e528dc14f85..d49669e92652 100644 --- a/fs/gfs2/quota.c +++ b/fs/gfs2/quota.c @@ -1427,8 +1427,8 @@ int gfs2_quotad(void *data) /* Check for & recover partially truncated inodes */ quotad_check_trunc_list(sdp); - if (freezing(current)) - refrigerator(); + try_to_freeze(); + t = min(quotad_timeo, statfs_timeo); prepare_to_wait(&sdp->sd_quota_wait, &wait, TASK_INTERRUPTIBLE); diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c index fea8dd661d2b..a96cff0c5f1d 100644 --- a/fs/jbd/journal.c +++ b/fs/jbd/journal.c @@ -166,7 +166,7 @@ loop: */ jbd_debug(1, "Now suspending kjournald\n"); spin_unlock(&journal->j_state_lock); - refrigerator(); + try_to_freeze(); spin_lock(&journal->j_state_lock); } else { /* diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c index 0fa0123151d3..c0a5f9f1b127 100644 --- a/fs/jbd2/journal.c +++ b/fs/jbd2/journal.c @@ -173,7 +173,7 @@ loop: */ jbd_debug(1, "Now suspending kjournald2\n"); write_unlock(&journal->j_state_lock); - refrigerator(); + try_to_freeze(); write_lock(&journal->j_state_lock); } else { /* diff --git a/fs/jfs/jfs_logmgr.c b/fs/jfs/jfs_logmgr.c index cc5f811ed383..2eb952c41a69 100644 --- a/fs/jfs/jfs_logmgr.c +++ b/fs/jfs/jfs_logmgr.c @@ -2349,7 +2349,7 @@ int jfsIOWait(void *arg) if (freezing(current)) { spin_unlock_irq(&log_redrive_lock); - refrigerator(); + try_to_freeze(); } else { set_current_state(TASK_INTERRUPTIBLE); spin_unlock_irq(&log_redrive_lock); diff --git a/fs/jfs/jfs_txnmgr.c b/fs/jfs/jfs_txnmgr.c index af9606057dde..bb8b661bcc50 100644 --- a/fs/jfs/jfs_txnmgr.c +++ b/fs/jfs/jfs_txnmgr.c @@ -2800,7 +2800,7 @@ int jfs_lazycommit(void *arg) if (freezing(current)) { LAZY_UNLOCK(flags); - refrigerator(); + try_to_freeze(); } else { DECLARE_WAITQUEUE(wq, current); @@ -2994,7 +2994,7 @@ int jfs_sync(void *arg) if (freezing(current)) { TXN_UNLOCK(); - refrigerator(); + try_to_freeze(); } else { set_current_state(TASK_INTERRUPTIBLE); TXN_UNLOCK(); diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c index bb24ab6c282f..0e72ad6f22aa 100644 --- a/fs/nilfs2/segment.c +++ b/fs/nilfs2/segment.c @@ -2470,7 +2470,7 @@ static int nilfs_segctor_thread(void *arg) if (freezing(current)) { spin_unlock(&sci->sc_state_lock); - refrigerator(); + try_to_freeze(); spin_lock(&sci->sc_state_lock); } else { DEFINE_WAIT(wait); diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c index cf0ac056815f..018829936d6d 100644 --- a/fs/xfs/xfs_buf.c +++ b/fs/xfs/xfs_buf.c @@ -1703,7 +1703,7 @@ xfsbufd( if (unlikely(freezing(current))) { set_bit(XBT_FORCE_SLEEP, &target->bt_flags); - refrigerator(); + try_to_freeze(); } else { clear_bit(XBT_FORCE_SLEEP, &target->bt_flags); } diff --git a/include/linux/freezer.h b/include/linux/freezer.h index a5386e3ee756..7a9427e9fe47 100644 --- a/include/linux/freezer.h +++ b/include/linux/freezer.h @@ -47,18 +47,17 @@ static inline bool should_send_signal(struct task_struct *p) /* Takes and releases task alloc lock using task_lock() */ extern int thaw_process(struct task_struct *p); -extern void refrigerator(void); +extern bool __refrigerator(void); extern int freeze_processes(void); extern int freeze_kernel_threads(void); extern void thaw_processes(void); -static inline int try_to_freeze(void) +static inline bool try_to_freeze(void) { - if (freezing(current)) { - refrigerator(); - return 1; - } else - return 0; + might_sleep(); + if (likely(!freezing(current))) + return false; + return __refrigerator(); } extern bool freeze_task(struct task_struct *p, bool sig_only); @@ -181,12 +180,12 @@ static inline void set_freeze_flag(struct task_struct *p) {} static inline void clear_freeze_flag(struct task_struct *p) {} static inline int thaw_process(struct task_struct *p) { return 1; } -static inline void refrigerator(void) {} +static inline bool __refrigerator(void) { return false; } static inline int freeze_processes(void) { return -ENOSYS; } static inline int freeze_kernel_threads(void) { return -ENOSYS; } static inline void thaw_processes(void) {} -static inline int try_to_freeze(void) { return 0; } +static inline bool try_to_freeze(void) { return false; } static inline void freezer_do_not_count(void) {} static inline void freezer_count(void) {} diff --git a/kernel/freezer.c b/kernel/freezer.c index 3f460104a9d6..732f14f5944f 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -23,10 +23,11 @@ static inline void frozen_process(void) } /* Refrigerator is place where frozen processes are stored :-). */ -void refrigerator(void) +bool __refrigerator(void) { /* Hmm, should we be allowed to suspend when there are realtime processes around? */ + bool was_frozen = false; long save; task_lock(current); @@ -35,7 +36,7 @@ void refrigerator(void) task_unlock(current); } else { task_unlock(current); - return; + return was_frozen; } save = current->state; pr_debug("%s entered refrigerator\n", current->comm); @@ -51,6 +52,7 @@ void refrigerator(void) set_current_state(TASK_UNINTERRUPTIBLE); if (!frozen(current)) break; + was_frozen = true; schedule(); } @@ -65,8 +67,10 @@ void refrigerator(void) * synchronization which depends on ordered task state change. */ set_current_state(save); + + return was_frozen; } -EXPORT_SYMBOL(refrigerator); +EXPORT_SYMBOL(__refrigerator); static void fake_signal_wake_up(struct task_struct *p) { From 8a32c441c1609f80e55df75422324a1151208f40 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:23 -0800 Subject: [PATCH 04/24] freezer: implement and use kthread_freezable_should_stop() Writeback and thinkpad_acpi have been using thaw_process() to prevent deadlock between the freezer and kthread_stop(); unfortunately, this is inherently racy - nothing prevents freezing from happening between thaw_process() and kthread_stop(). This patch implements kthread_freezable_should_stop() which enters refrigerator if necessary but is guaranteed to return if kthread_stop() is invoked. Both thaw_process() users are converted to use the new function. Note that this deadlock condition exists for many of freezable kthreads. They need to be converted to use the new should_stop or freezable workqueue. Tested with synthetic test case. Signed-off-by: Tejun Heo Acked-by: Henrique de Moraes Holschuh Cc: Jens Axboe Cc: Oleg Nesterov --- drivers/platform/x86/thinkpad_acpi.c | 15 ++++++--------- fs/fs-writeback.c | 4 +--- include/linux/freezer.h | 6 +++--- include/linux/kthread.h | 1 + kernel/freezer.c | 6 ++++-- kernel/kthread.c | 25 +++++++++++++++++++++++++ mm/backing-dev.c | 8 ++------ 7 files changed, 42 insertions(+), 23 deletions(-) diff --git a/drivers/platform/x86/thinkpad_acpi.c b/drivers/platform/x86/thinkpad_acpi.c index 7b828680b21d..4b11fc91fa7d 100644 --- a/drivers/platform/x86/thinkpad_acpi.c +++ b/drivers/platform/x86/thinkpad_acpi.c @@ -2456,8 +2456,9 @@ static int hotkey_kthread(void *data) u32 poll_mask, event_mask; unsigned int si, so; unsigned long t; - unsigned int change_detector, must_reset; + unsigned int change_detector; unsigned int poll_freq; + bool was_frozen; mutex_lock(&hotkey_thread_mutex); @@ -2488,14 +2489,14 @@ static int hotkey_kthread(void *data) t = 100; /* should never happen... */ } t = msleep_interruptible(t); - if (unlikely(kthread_should_stop())) + if (unlikely(kthread_freezable_should_stop(&was_frozen))) break; - must_reset = try_to_freeze(); - if (t > 0 && !must_reset) + + if (t > 0 && !was_frozen) continue; mutex_lock(&hotkey_thread_data_mutex); - if (must_reset || hotkey_config_change != change_detector) { + if (was_frozen || hotkey_config_change != change_detector) { /* forget old state on thaw or config change */ si = so; t = 0; @@ -2528,10 +2529,6 @@ exit: static void hotkey_poll_stop_sync(void) { if (tpacpi_hotkey_task) { - if (frozen(tpacpi_hotkey_task) || - freezing(tpacpi_hotkey_task)) - thaw_process(tpacpi_hotkey_task); - kthread_stop(tpacpi_hotkey_task); tpacpi_hotkey_task = NULL; mutex_lock(&hotkey_thread_mutex); diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 73c3992b2bb4..271fde50f0ee 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -947,7 +947,7 @@ int bdi_writeback_thread(void *data) trace_writeback_thread_start(bdi); - while (!kthread_should_stop()) { + while (!kthread_freezable_should_stop(NULL)) { /* * Remove own delayed wake-up timer, since we are already awake * and we'll take care of the preriodic write-back. @@ -977,8 +977,6 @@ int bdi_writeback_thread(void *data) */ schedule(); } - - try_to_freeze(); } /* Flush any work that raced with us exiting */ diff --git a/include/linux/freezer.h b/include/linux/freezer.h index 7a9427e9fe47..d02b78448b0f 100644 --- a/include/linux/freezer.h +++ b/include/linux/freezer.h @@ -47,7 +47,7 @@ static inline bool should_send_signal(struct task_struct *p) /* Takes and releases task alloc lock using task_lock() */ extern int thaw_process(struct task_struct *p); -extern bool __refrigerator(void); +extern bool __refrigerator(bool check_kthr_stop); extern int freeze_processes(void); extern int freeze_kernel_threads(void); extern void thaw_processes(void); @@ -57,7 +57,7 @@ static inline bool try_to_freeze(void) might_sleep(); if (likely(!freezing(current))) return false; - return __refrigerator(); + return __refrigerator(false); } extern bool freeze_task(struct task_struct *p, bool sig_only); @@ -180,7 +180,7 @@ static inline void set_freeze_flag(struct task_struct *p) {} static inline void clear_freeze_flag(struct task_struct *p) {} static inline int thaw_process(struct task_struct *p) { return 1; } -static inline bool __refrigerator(void) { return false; } +static inline bool __refrigerator(bool check_kthr_stop) { return false; } static inline int freeze_processes(void) { return -ENOSYS; } static inline int freeze_kernel_threads(void) { return -ENOSYS; } static inline void thaw_processes(void) {} diff --git a/include/linux/kthread.h b/include/linux/kthread.h index 5cac19b3a266..0714b24c0e45 100644 --- a/include/linux/kthread.h +++ b/include/linux/kthread.h @@ -35,6 +35,7 @@ struct task_struct *kthread_create_on_node(int (*threadfn)(void *data), void kthread_bind(struct task_struct *k, unsigned int cpu); int kthread_stop(struct task_struct *k); int kthread_should_stop(void); +bool kthread_freezable_should_stop(bool *was_frozen); void *kthread_data(struct task_struct *k); int kthreadd(void *unused); diff --git a/kernel/freezer.c b/kernel/freezer.c index 732f14f5944f..b83c30e9483a 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -9,6 +9,7 @@ #include #include #include +#include /* * freezing is complete, mark current process as frozen @@ -23,7 +24,7 @@ static inline void frozen_process(void) } /* Refrigerator is place where frozen processes are stored :-). */ -bool __refrigerator(void) +bool __refrigerator(bool check_kthr_stop) { /* Hmm, should we be allowed to suspend when there are realtime processes around? */ @@ -50,7 +51,8 @@ bool __refrigerator(void) for (;;) { set_current_state(TASK_UNINTERRUPTIBLE); - if (!frozen(current)) + if (!frozen(current) || + (check_kthr_stop && kthread_should_stop())) break; was_frozen = true; schedule(); diff --git a/kernel/kthread.c b/kernel/kthread.c index b6d216a92639..1c36deaae2f1 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -58,6 +58,31 @@ int kthread_should_stop(void) } EXPORT_SYMBOL(kthread_should_stop); +/** + * kthread_freezable_should_stop - should this freezable kthread return now? + * @was_frozen: optional out parameter, indicates whether %current was frozen + * + * kthread_should_stop() for freezable kthreads, which will enter + * refrigerator if necessary. This function is safe from kthread_stop() / + * freezer deadlock and freezable kthreads should use this function instead + * of calling try_to_freeze() directly. + */ +bool kthread_freezable_should_stop(bool *was_frozen) +{ + bool frozen = false; + + might_sleep(); + + if (unlikely(freezing(current))) + frozen = __refrigerator(true); + + if (was_frozen) + *was_frozen = frozen; + + return kthread_should_stop(); +} +EXPORT_SYMBOL_GPL(kthread_freezable_should_stop); + /** * kthread_data - return data value specified on kthread creation * @task: kthread task in question diff --git a/mm/backing-dev.c b/mm/backing-dev.c index 71034f41a2ba..7ba8feae11b8 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -600,14 +600,10 @@ static void bdi_wb_shutdown(struct backing_dev_info *bdi) /* * Finally, kill the kernel thread. We don't need to be RCU - * safe anymore, since the bdi is gone from visibility. Force - * unfreeze of the thread before calling kthread_stop(), otherwise - * it would never exet if it is currently stuck in the refrigerator. + * safe anymore, since the bdi is gone from visibility. */ - if (bdi->wb.task) { - thaw_process(bdi->wb.task); + if (bdi->wb.task) kthread_stop(bdi->wb.task); - } } /* From a5be2d0d1a8746e7be5210e3d6b904455000443c Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:23 -0800 Subject: [PATCH 05/24] freezer: rename thaw_process() to __thaw_task() and simplify the implementation thaw_process() now has only internal users - system and cgroup freezers. Remove the unnecessary return value, rename, unexport and collapse __thaw_process() into it. This will help further updates to the freezer code. -v3: oom_kill grew a use of thaw_process() while this patch was pending. Convert it to use __thaw_task() for now. In the longer term, this should be handled by allowing tasks to die if killed even if it's frozen. -v2: minor style update as suggested by Matt. Signed-off-by: Tejun Heo Cc: Paul Menage Cc: Matt Helsley --- include/linux/freezer.h | 3 +-- kernel/cgroup_freezer.c | 7 +++---- kernel/freezer.c | 31 ++++++++++++------------------- kernel/power/process.c | 2 +- mm/oom_kill.c | 2 +- 5 files changed, 18 insertions(+), 27 deletions(-) diff --git a/include/linux/freezer.h b/include/linux/freezer.h index d02b78448b0f..ba4f512d2938 100644 --- a/include/linux/freezer.h +++ b/include/linux/freezer.h @@ -45,7 +45,7 @@ static inline bool should_send_signal(struct task_struct *p) } /* Takes and releases task alloc lock using task_lock() */ -extern int thaw_process(struct task_struct *p); +extern void __thaw_task(struct task_struct *t); extern bool __refrigerator(bool check_kthr_stop); extern int freeze_processes(void); @@ -178,7 +178,6 @@ static inline int frozen(struct task_struct *p) { return 0; } static inline int freezing(struct task_struct *p) { return 0; } static inline void set_freeze_flag(struct task_struct *p) {} static inline void clear_freeze_flag(struct task_struct *p) {} -static inline int thaw_process(struct task_struct *p) { return 1; } static inline bool __refrigerator(bool check_kthr_stop) { return false; } static inline int freeze_processes(void) { return -ENOSYS; } diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c index 5e828a2ca8e6..a6d405a86ee0 100644 --- a/kernel/cgroup_freezer.c +++ b/kernel/cgroup_freezer.c @@ -130,7 +130,7 @@ struct cgroup_subsys freezer_subsys; * write_lock css_set_lock (cgroup iterator start) * task->alloc_lock * read_lock css_set_lock (cgroup iterator start) - * task->alloc_lock (inside thaw_process(), prevents race with refrigerator()) + * task->alloc_lock (inside __thaw_task(), prevents race with refrigerator()) * sighand->siglock */ static struct cgroup_subsys_state *freezer_create(struct cgroup_subsys *ss, @@ -300,9 +300,8 @@ static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) struct task_struct *task; cgroup_iter_start(cgroup, &it); - while ((task = cgroup_iter_next(cgroup, &it))) { - thaw_process(task); - } + while ((task = cgroup_iter_next(cgroup, &it))) + __thaw_task(task); cgroup_iter_end(cgroup, &it); freezer->state = CGROUP_THAWED; diff --git a/kernel/freezer.c b/kernel/freezer.c index b83c30e9483a..c851d588e29f 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -145,18 +145,8 @@ void cancel_freezing(struct task_struct *p) } } -static int __thaw_process(struct task_struct *p) -{ - if (frozen(p)) { - p->flags &= ~PF_FROZEN; - return 1; - } - clear_freeze_flag(p); - return 0; -} - /* - * Wake up a frozen process + * Wake up a frozen task * * task_lock() is needed to prevent the race with refrigerator() which may * occur if the freezing of tasks fails. Namely, without the lock, if the @@ -164,15 +154,18 @@ static int __thaw_process(struct task_struct *p) * refrigerator() could call frozen_process(), in which case the task would be * frozen and no one would thaw it. */ -int thaw_process(struct task_struct *p) +void __thaw_task(struct task_struct *p) { + bool was_frozen; + task_lock(p); - if (__thaw_process(p) == 1) { - task_unlock(p); - wake_up_process(p); - return 1; - } + was_frozen = frozen(p); + if (was_frozen) + p->flags &= ~PF_FROZEN; + else + clear_freeze_flag(p); task_unlock(p); - return 0; + + if (was_frozen) + wake_up_process(p); } -EXPORT_SYMBOL(thaw_process); diff --git a/kernel/power/process.c b/kernel/power/process.c index addbbe5531bc..fe2787207f00 100644 --- a/kernel/power/process.c +++ b/kernel/power/process.c @@ -186,7 +186,7 @@ static void thaw_tasks(bool nosig_only) if (cgroup_freezing_or_frozen(p)) continue; - thaw_process(p); + __thaw_task(p); } while_each_thread(g, p); read_unlock(&tasklist_lock); } diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 76f2c5ae908e..3134ee2fb2e8 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -328,7 +328,7 @@ static struct task_struct *select_bad_process(unsigned int *ppoints, */ if (test_tsk_thread_flag(p, TIF_MEMDIE)) { if (unlikely(frozen(p))) - thaw_process(p); + __thaw_task(p); return ERR_PTR(-1UL); } if (!p->mm) From a585042f7b933539a0b6bc63650c2d49ffb2e55d Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:23 -0800 Subject: [PATCH 06/24] freezer: remove racy clear_freeze_flag() and set PF_NOFREEZE on dead tasks clear_freeze_flag() in exit_mm() is racy. Freezing can start afterwards. Remove it. Skipping freezer for exiting task will be properly implemented later. Also, freezable() was testing exit_state directly to make system freezer ignore dead tasks. Let the exiting task set PF_NOFREEZE after entering TASK_DEAD instead. Signed-off-by: Tejun Heo Cc: Oleg Nesterov --- kernel/exit.c | 3 +-- kernel/power/process.c | 3 +-- 2 files changed, 2 insertions(+), 4 deletions(-) diff --git a/kernel/exit.c b/kernel/exit.c index d0b7d988f873..95a4141d07e7 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -679,8 +679,6 @@ static void exit_mm(struct task_struct * tsk) tsk->mm = NULL; up_read(&mm->mmap_sem); enter_lazy_tlb(mm, current); - /* We don't want this task to be frozen prematurely */ - clear_freeze_flag(tsk); task_unlock(tsk); mm_update_next_owner(mm); mmput(mm); @@ -1040,6 +1038,7 @@ NORET_TYPE void do_exit(long code) exit_rcu(); /* causes final put_task_struct in finish_task_switch(). */ tsk->state = TASK_DEAD; + tsk->flags |= PF_NOFREEZE; /* tell freezer to ignore us */ schedule(); BUG(); /* Avoid "noreturn function does return". */ diff --git a/kernel/power/process.c b/kernel/power/process.c index fe2787207f00..23822dc14b6c 100644 --- a/kernel/power/process.c +++ b/kernel/power/process.c @@ -25,8 +25,7 @@ static inline int freezable(struct task_struct * p) { if ((p == current) || - (p->flags & PF_NOFREEZE) || - (p->exit_state != 0)) + (p->flags & PF_NOFREEZE)) return 0; return 1; } From 6cd8dedcdd8e8de01391a7cf25f0b2afeb24f8f4 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:23 -0800 Subject: [PATCH 07/24] freezer: don't distinguish nosig tasks on thaw There's no point in thawing nosig tasks before others. There's no ordering requirement between the two groups on thaw, which the staged thawing can't guarantee anyway. Simplify thaw_processes() by removing the distinction and collapsing thaw_tasks() into thaw_processes(). This will help further updates to freezer. Signed-off-by: Tejun Heo --- kernel/power/process.c | 20 +++++++------------- 1 file changed, 7 insertions(+), 13 deletions(-) diff --git a/kernel/power/process.c b/kernel/power/process.c index 23822dc14b6c..9db048fb0d70 100644 --- a/kernel/power/process.c +++ b/kernel/power/process.c @@ -170,34 +170,28 @@ int freeze_kernel_threads(void) return error; } -static void thaw_tasks(bool nosig_only) +void thaw_processes(void) { struct task_struct *g, *p; + oom_killer_enable(); + + printk("Restarting tasks ... "); + + thaw_workqueues(); + read_lock(&tasklist_lock); do_each_thread(g, p) { if (!freezable(p)) continue; - if (nosig_only && should_send_signal(p)) - continue; - if (cgroup_freezing_or_frozen(p)) continue; __thaw_task(p); } while_each_thread(g, p); read_unlock(&tasklist_lock); -} -void thaw_processes(void) -{ - oom_killer_enable(); - - printk("Restarting tasks ... "); - thaw_workqueues(); - thaw_tasks(true); - thaw_tasks(false); schedule(); printk("done.\n"); } From 0c9af09262864a2744091ee94c98c4a8fd60c98b Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:24 -0800 Subject: [PATCH 08/24] freezer: use dedicated lock instead of task_lock() + memory barrier Freezer synchronization is needlessly complicated - it's by no means a hot path and the priority is staying unintrusive and safe. This patch makes it simply use a dedicated lock instead of piggy-backing on task_lock() and playing with memory barriers. On the failure path of try_to_freeze_tasks(), locking is moved from it to cancel_freezing(). This makes the frozen() test racy but the race here is a non-issue as the warning is printed for tasks which failed to enter frozen for 20 seconds and race on PF_FROZEN at the last moment doesn't change anything. This simplifies freezer implementation and eases further changes including some race fixes. Signed-off-by: Tejun Heo --- kernel/freezer.c | 82 +++++++++++++++++++----------------------- kernel/power/process.c | 2 -- 2 files changed, 36 insertions(+), 48 deletions(-) diff --git a/kernel/freezer.c b/kernel/freezer.c index c851d588e29f..4130e48649bb 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -11,17 +11,8 @@ #include #include -/* - * freezing is complete, mark current process as frozen - */ -static inline void frozen_process(void) -{ - if (!unlikely(current->flags & PF_NOFREEZE)) { - current->flags |= PF_FROZEN; - smp_wmb(); - } - clear_freeze_flag(current); -} +/* protects freezing and frozen transitions */ +static DEFINE_SPINLOCK(freezer_lock); /* Refrigerator is place where frozen processes are stored :-). */ bool __refrigerator(bool check_kthr_stop) @@ -31,14 +22,16 @@ bool __refrigerator(bool check_kthr_stop) bool was_frozen = false; long save; - task_lock(current); - if (freezing(current)) { - frozen_process(); - task_unlock(current); - } else { - task_unlock(current); + spin_lock_irq(&freezer_lock); + if (!freezing(current)) { + spin_unlock_irq(&freezer_lock); return was_frozen; } + if (!(current->flags & PF_NOFREEZE)) + current->flags |= PF_FROZEN; + clear_freeze_flag(current); + spin_unlock_irq(&freezer_lock); + save = current->state; pr_debug("%s entered refrigerator\n", current->comm); @@ -99,21 +92,18 @@ static void fake_signal_wake_up(struct task_struct *p) */ bool freeze_task(struct task_struct *p, bool sig_only) { - /* - * We first check if the task is freezing and next if it has already - * been frozen to avoid the race with frozen_process() which first marks - * the task as frozen and next clears its TIF_FREEZE. - */ - if (!freezing(p)) { - smp_rmb(); - if (frozen(p)) - return false; + unsigned long flags; + bool ret = false; - if (!sig_only || should_send_signal(p)) - set_freeze_flag(p); - else - return false; - } + spin_lock_irqsave(&freezer_lock, flags); + + if (sig_only && !should_send_signal(p)) + goto out_unlock; + + if (frozen(p)) + goto out_unlock; + + set_freeze_flag(p); if (should_send_signal(p)) { fake_signal_wake_up(p); @@ -123,26 +113,28 @@ bool freeze_task(struct task_struct *p, bool sig_only) * TASK_RUNNING transition can't race with task state * testing in try_to_freeze_tasks(). */ - } else if (sig_only) { - return false; } else { wake_up_state(p, TASK_INTERRUPTIBLE); } - - return true; + ret = true; +out_unlock: + spin_unlock_irqrestore(&freezer_lock, flags); + return ret; } void cancel_freezing(struct task_struct *p) { unsigned long flags; + spin_lock_irqsave(&freezer_lock, flags); if (freezing(p)) { pr_debug(" clean up: %s\n", p->comm); clear_freeze_flag(p); - spin_lock_irqsave(&p->sighand->siglock, flags); + spin_lock(&p->sighand->siglock); recalc_sigpending_and_wake(p); - spin_unlock_irqrestore(&p->sighand->siglock, flags); + spin_unlock(&p->sighand->siglock); } + spin_unlock_irqrestore(&freezer_lock, flags); } /* @@ -156,16 +148,14 @@ void cancel_freezing(struct task_struct *p) */ void __thaw_task(struct task_struct *p) { - bool was_frozen; + unsigned long flags; - task_lock(p); - was_frozen = frozen(p); - if (was_frozen) + spin_lock_irqsave(&freezer_lock, flags); + if (frozen(p)) { p->flags &= ~PF_FROZEN; - else - clear_freeze_flag(p); - task_unlock(p); - - if (was_frozen) wake_up_process(p); + } else { + clear_freeze_flag(p); + } + spin_unlock_irqrestore(&freezer_lock, flags); } diff --git a/kernel/power/process.c b/kernel/power/process.c index 9db048fb0d70..bd420ca48261 100644 --- a/kernel/power/process.c +++ b/kernel/power/process.c @@ -118,11 +118,9 @@ static int try_to_freeze_tasks(bool sig_only) read_lock(&tasklist_lock); do_each_thread(g, p) { - task_lock(p); if (!wakeup && freezing(p) && !freezer_should_skip(p)) sched_show_task(p); cancel_freezing(p); - task_unlock(p); } while_each_thread(g, p); read_unlock(&tasklist_lock); } else { From 6907483b4e803a20f0b48cc9afa3817420ce61c5 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:24 -0800 Subject: [PATCH 09/24] freezer: make freezing indicate freeze condition in effect Currently freezing (TIF_FREEZE) and frozen (PF_FROZEN) states are interlocked - freezing is set to request freeze and when the task actually freezes, it clears freezing and sets frozen. This interlocking makes things more complex than necessary - freezing doesn't mean there's freezing condition in effect and frozen doesn't match the task actually entering and leaving frozen state (it's cleared by the thawing task). This patch makes freezing indicate that freeze condition is in effect. A task enters and stays frozen if freezing. This makes PF_FROZEN manipulation done only by the task itself and prevents wakeup from __thaw_task() leaking outside of refrigerator. The only place which needs to tell freezing && !frozen is try_to_freeze_task() to whine about tasks which don't enter frozen. It's updated to test the condition explicitly. With the change, frozen() state my linger after __thaw_task() until the task wakes up and exits fridge. This can trigger BUG_ON() in update_if_frozen(). Work it around by testing freezing() && frozen() instead of frozen(). -v2: Oleg pointed out missing re-check of freezing() when trying to clear FROZEN and possible spurious BUG_ON() trigger in update_if_frozen(). Both fixed. Signed-off-by: Tejun Heo Cc: Oleg Nesterov Cc: Paul Menage --- kernel/cgroup_freezer.c | 2 +- kernel/freezer.c | 42 +++++++++++++++++++++++------------------ kernel/power/process.c | 3 ++- 3 files changed, 27 insertions(+), 20 deletions(-) diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c index a6d405a86ee0..cd27b0825560 100644 --- a/kernel/cgroup_freezer.c +++ b/kernel/cgroup_freezer.c @@ -231,7 +231,7 @@ static void update_if_frozen(struct cgroup *cgroup, cgroup_iter_start(cgroup, &it); while ((task = cgroup_iter_next(cgroup, &it))) { ntotal++; - if (frozen(task)) + if (freezing(task) && frozen(task)) nfrozen++; } diff --git a/kernel/freezer.c b/kernel/freezer.c index 4130e48649bb..a8822be43da0 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -22,14 +22,19 @@ bool __refrigerator(bool check_kthr_stop) bool was_frozen = false; long save; + /* + * Enter FROZEN. If NOFREEZE, schedule immediate thawing by + * clearing freezing. + */ spin_lock_irq(&freezer_lock); +repeat: if (!freezing(current)) { spin_unlock_irq(&freezer_lock); return was_frozen; } - if (!(current->flags & PF_NOFREEZE)) - current->flags |= PF_FROZEN; - clear_freeze_flag(current); + if (current->flags & PF_NOFREEZE) + clear_freeze_flag(current); + current->flags |= PF_FROZEN; spin_unlock_irq(&freezer_lock); save = current->state; @@ -44,7 +49,7 @@ bool __refrigerator(bool check_kthr_stop) for (;;) { set_current_state(TASK_UNINTERRUPTIBLE); - if (!frozen(current) || + if (!freezing(current) || (check_kthr_stop && kthread_should_stop())) break; was_frozen = true; @@ -54,6 +59,13 @@ bool __refrigerator(bool check_kthr_stop) /* Remove the accounting blocker */ current->flags &= ~PF_FREEZING; + /* leave FROZEN */ + spin_lock_irq(&freezer_lock); + if (freezing(current)) + goto repeat; + current->flags &= ~PF_FROZEN; + spin_unlock_irq(&freezer_lock); + pr_debug("%s left refrigerator\n", current->comm); /* @@ -137,25 +149,19 @@ void cancel_freezing(struct task_struct *p) spin_unlock_irqrestore(&freezer_lock, flags); } -/* - * Wake up a frozen task - * - * task_lock() is needed to prevent the race with refrigerator() which may - * occur if the freezing of tasks fails. Namely, without the lock, if the - * freezing of tasks failed, thaw_tasks() might have run before a task in - * refrigerator() could call frozen_process(), in which case the task would be - * frozen and no one would thaw it. - */ void __thaw_task(struct task_struct *p) { unsigned long flags; + /* + * Clear freezing and kick @p if FROZEN. Clearing is guaranteed to + * be visible to @p as waking up implies wmb. Waking up inside + * freezer_lock also prevents wakeups from leaking outside + * refrigerator. + */ spin_lock_irqsave(&freezer_lock, flags); - if (frozen(p)) { - p->flags &= ~PF_FROZEN; + clear_freeze_flag(p); + if (frozen(p)) wake_up_process(p); - } else { - clear_freeze_flag(p); - } spin_unlock_irqrestore(&freezer_lock, flags); } diff --git a/kernel/power/process.c b/kernel/power/process.c index bd420ca48261..e6e2739190b5 100644 --- a/kernel/power/process.c +++ b/kernel/power/process.c @@ -118,7 +118,8 @@ static int try_to_freeze_tasks(bool sig_only) read_lock(&tasklist_lock); do_each_thread(g, p) { - if (!wakeup && freezing(p) && !freezer_should_skip(p)) + if (!wakeup && !freezer_should_skip(p) && + freezing(p) && !frozen(p)) sched_show_task(p); cancel_freezing(p); } while_each_thread(g, p); From 85f1d476653f52c97ca75466b2494e67c1cbd25d Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:24 -0800 Subject: [PATCH 10/24] freezer: test freezable conditions while holding freezer_lock try_to_freeze_tasks() and thaw_processes() use freezable() and frozen() as preliminary tests before initiating operations on a task. These are done without any synchronization and hinder with synchronization cleanup without any real performance benefits. In try_to_freeze_tasks(), open code self test and move PF_NOFREEZE and frozen() tests inside freezer_lock in freeze_task(). thaw_processes() can simply drop freezable() test as frozen() test in __thaw_task() is enough. Note: This used to be a part of larger patch to fix set_freezable() race. Separated out to satisfy ordering among dependent fixes. Signed-off-by: Tejun Heo Cc: Oleg Nesterov --- kernel/freezer.c | 3 ++- kernel/power/process.c | 16 +--------------- 2 files changed, 3 insertions(+), 16 deletions(-) diff --git a/kernel/freezer.c b/kernel/freezer.c index a8822be43da0..a257ecd37c48 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -109,7 +109,8 @@ bool freeze_task(struct task_struct *p, bool sig_only) spin_lock_irqsave(&freezer_lock, flags); - if (sig_only && !should_send_signal(p)) + if ((p->flags & PF_NOFREEZE) || + (sig_only && !should_send_signal(p))) goto out_unlock; if (frozen(p)) diff --git a/kernel/power/process.c b/kernel/power/process.c index e6e2739190b5..e59676f5811d 100644 --- a/kernel/power/process.c +++ b/kernel/power/process.c @@ -22,14 +22,6 @@ */ #define TIMEOUT (20 * HZ) -static inline int freezable(struct task_struct * p) -{ - if ((p == current) || - (p->flags & PF_NOFREEZE)) - return 0; - return 1; -} - static int try_to_freeze_tasks(bool sig_only) { struct task_struct *g, *p; @@ -52,10 +44,7 @@ static int try_to_freeze_tasks(bool sig_only) todo = 0; read_lock(&tasklist_lock); do_each_thread(g, p) { - if (frozen(p) || !freezable(p)) - continue; - - if (!freeze_task(p, sig_only)) + if (p == current || !freeze_task(p, sig_only)) continue; /* @@ -181,9 +170,6 @@ void thaw_processes(void) read_lock(&tasklist_lock); do_each_thread(g, p) { - if (!freezable(p)) - continue; - if (cgroup_freezing_or_frozen(p)) continue; From 376fede80e74d98b49d1ba9ac18f23c9fd026ddd Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:24 -0800 Subject: [PATCH 11/24] freezer: kill PF_FREEZING With the previous changes, there's no meaningful difference between PF_FREEZING and PF_FROZEN. Remove PF_FREEZING and use PF_FROZEN instead in task_contributes_to_load(). Signed-off-by: Tejun Heo --- include/linux/sched.h | 3 +-- kernel/freezer.c | 6 ------ 2 files changed, 1 insertion(+), 8 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 68daf4f27e2c..d12bd03b688f 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -220,7 +220,7 @@ extern char ___assert_task_state[1 - 2*!!( ((task->state & (__TASK_STOPPED | __TASK_TRACED)) != 0) #define task_contributes_to_load(task) \ ((task->state & TASK_UNINTERRUPTIBLE) != 0 && \ - (task->flags & PF_FREEZING) == 0) + (task->flags & PF_FROZEN) == 0) #define __set_task_state(tsk, state_value) \ do { (tsk)->state = (state_value); } while (0) @@ -1773,7 +1773,6 @@ extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t * #define PF_MEMALLOC 0x00000800 /* Allocating memory */ #define PF_NPROC_EXCEEDED 0x00001000 /* set_user noticed that RLIMIT_NPROC was exceeded */ #define PF_USED_MATH 0x00002000 /* if unset the fpu must be initialized before use */ -#define PF_FREEZING 0x00004000 /* freeze in progress. do not account to load */ #define PF_NOFREEZE 0x00008000 /* this thread should not be frozen */ #define PF_FROZEN 0x00010000 /* frozen for system suspend */ #define PF_FSTRANS 0x00020000 /* inside a filesystem transaction */ diff --git a/kernel/freezer.c b/kernel/freezer.c index a257ecd37c48..b8b562124ba9 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -44,9 +44,6 @@ repeat: recalc_sigpending(); /* We sent fake signal, clean it up */ spin_unlock_irq(¤t->sighand->siglock); - /* prevent accounting of that task to load */ - current->flags |= PF_FREEZING; - for (;;) { set_current_state(TASK_UNINTERRUPTIBLE); if (!freezing(current) || @@ -56,9 +53,6 @@ repeat: schedule(); } - /* Remove the accounting blocker */ - current->flags &= ~PF_FREEZING; - /* leave FROZEN */ spin_lock_irq(&freezer_lock); if (freezing(current)) From 03afed8bc296fa70186ba832c1126228bb992465 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:24 -0800 Subject: [PATCH 12/24] freezer: clean up freeze_processes() failure path freeze_processes() failure path is rather messy. Freezing is canceled for workqueues and tasks which aren't frozen yet but frozen tasks are left alone and should be thawed by the caller and of course some callers (xen and kexec) didn't do it. This patch updates __thaw_task() to handle cancelation correctly and makes freeze_processes() and freeze_kernel_threads() call thaw_processes() on failure instead so that the system is fully thawed on failure. Unnecessary [suspend_]thaw_processes() calls are removed from kernel/power/hibernate.c, suspend.c and user.c. While at it, restructure error checking if clause in suspend_prepare() to be less weird. -v2: Srivatsa spotted missing removal of suspend_thaw_processes() in suspend_prepare() and error in commit message. Updated. Signed-off-by: Tejun Heo Acked-by: Srivatsa S. Bhat --- include/linux/freezer.h | 1 - kernel/freezer.c | 25 +++++++++---------------- kernel/power/hibernate.c | 15 ++------------- kernel/power/process.c | 16 ++++++++-------- kernel/power/suspend.c | 8 +++----- kernel/power/user.c | 4 +--- 6 files changed, 23 insertions(+), 46 deletions(-) diff --git a/include/linux/freezer.h b/include/linux/freezer.h index ba4f512d2938..93f411a52872 100644 --- a/include/linux/freezer.h +++ b/include/linux/freezer.h @@ -61,7 +61,6 @@ static inline bool try_to_freeze(void) } extern bool freeze_task(struct task_struct *p, bool sig_only); -extern void cancel_freezing(struct task_struct *p); #ifdef CONFIG_CGROUP_FREEZER extern int cgroup_freezing_or_frozen(struct task_struct *task); diff --git a/kernel/freezer.c b/kernel/freezer.c index b8b562124ba9..11e32d419dec 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -129,21 +129,6 @@ out_unlock: return ret; } -void cancel_freezing(struct task_struct *p) -{ - unsigned long flags; - - spin_lock_irqsave(&freezer_lock, flags); - if (freezing(p)) { - pr_debug(" clean up: %s\n", p->comm); - clear_freeze_flag(p); - spin_lock(&p->sighand->siglock); - recalc_sigpending_and_wake(p); - spin_unlock(&p->sighand->siglock); - } - spin_unlock_irqrestore(&freezer_lock, flags); -} - void __thaw_task(struct task_struct *p) { unsigned long flags; @@ -153,10 +138,18 @@ void __thaw_task(struct task_struct *p) * be visible to @p as waking up implies wmb. Waking up inside * freezer_lock also prevents wakeups from leaking outside * refrigerator. + * + * If !FROZEN, @p hasn't reached refrigerator, recalc sigpending to + * avoid leaving dangling TIF_SIGPENDING behind. */ spin_lock_irqsave(&freezer_lock, flags); clear_freeze_flag(p); - if (frozen(p)) + if (frozen(p)) { wake_up_process(p); + } else { + spin_lock(&p->sighand->siglock); + recalc_sigpending_and_wake(p); + spin_unlock(&p->sighand->siglock); + } spin_unlock_irqrestore(&freezer_lock, flags); } diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c index 196c01268ebd..ba2319ffc860 100644 --- a/kernel/power/hibernate.c +++ b/kernel/power/hibernate.c @@ -607,17 +607,6 @@ static void power_down(void) while(1); } -static int prepare_processes(void) -{ - int error = 0; - - if (freeze_processes()) { - error = -EBUSY; - thaw_processes(); - } - return error; -} - /** * hibernate - Carry out system hibernation, including saving the image. */ @@ -650,7 +639,7 @@ int hibernate(void) sys_sync(); printk("done.\n"); - error = prepare_processes(); + error = freeze_processes(); if (error) goto Finish; @@ -811,7 +800,7 @@ static int software_resume(void) goto close_finish; pr_debug("PM: Preparing processes for restore.\n"); - error = prepare_processes(); + error = freeze_processes(); if (error) { swsusp_close(FMODE_READ); goto Done; diff --git a/kernel/power/process.c b/kernel/power/process.c index e59676f5811d..ce643838a00c 100644 --- a/kernel/power/process.c +++ b/kernel/power/process.c @@ -91,11 +91,6 @@ static int try_to_freeze_tasks(bool sig_only) elapsed_csecs = elapsed_csecs64; if (todo) { - /* This does not unfreeze processes that are already frozen - * (we have slightly ugly calling convention in that respect, - * and caller must call thaw_processes() if something fails), - * but it cleans up leftover PF_FREEZE requests. - */ printk("\n"); printk(KERN_ERR "Freezing of tasks %s after %d.%02d seconds " "(%d tasks refusing to freeze, wq_busy=%d):\n", @@ -103,14 +98,11 @@ static int try_to_freeze_tasks(bool sig_only) elapsed_csecs / 100, elapsed_csecs % 100, todo - wq_busy, wq_busy); - thaw_workqueues(); - read_lock(&tasklist_lock); do_each_thread(g, p) { if (!wakeup && !freezer_should_skip(p) && freezing(p) && !frozen(p)) sched_show_task(p); - cancel_freezing(p); } while_each_thread(g, p); read_unlock(&tasklist_lock); } else { @@ -123,6 +115,8 @@ static int try_to_freeze_tasks(bool sig_only) /** * freeze_processes - Signal user space processes to enter the refrigerator. + * + * On success, returns 0. On failure, -errno and system is fully thawed. */ int freeze_processes(void) { @@ -137,11 +131,15 @@ int freeze_processes(void) printk("\n"); BUG_ON(in_atomic()); + if (error) + thaw_processes(); return error; } /** * freeze_kernel_threads - Make freezable kernel threads go to the refrigerator. + * + * On success, returns 0. On failure, -errno and system is fully thawed. */ int freeze_kernel_threads(void) { @@ -155,6 +153,8 @@ int freeze_kernel_threads(void) printk("\n"); BUG_ON(in_atomic()); + if (error) + thaw_processes(); return error; } diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c index 4953dc054c53..d336b27d1104 100644 --- a/kernel/power/suspend.c +++ b/kernel/power/suspend.c @@ -106,13 +106,11 @@ static int suspend_prepare(void) goto Finish; error = suspend_freeze_processes(); - if (error) { - suspend_stats.failed_freeze++; - dpm_save_failed_step(SUSPEND_FREEZE); - } else + if (!error) return 0; - suspend_thaw_processes(); + suspend_stats.failed_freeze++; + dpm_save_failed_step(SUSPEND_FREEZE); usermodehelper_enable(); Finish: pm_notifier_call_chain(PM_POST_SUSPEND); diff --git a/kernel/power/user.c b/kernel/power/user.c index 6d8f535c2b88..7cc3f5bc5c24 100644 --- a/kernel/power/user.c +++ b/kernel/power/user.c @@ -257,10 +257,8 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd, break; error = freeze_processes(); - if (error) { - thaw_processes(); + if (error) usermodehelper_enable(); - } if (!error) data->frozen = 1; break; From 22b4e111fa01a1147aa562ceaf18a752a928ef4e Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:25 -0800 Subject: [PATCH 13/24] cgroup_freezer: prepare for removal of TIF_FREEZE TIF_FREEZE will be removed soon and freezing() will directly test whether any freezing condition is in effect. Make the following changes in preparation. * Rename cgroup_freezing_or_frozen() to cgroup_freezing() and make it return bool. * Make cgroup_freezing() access task_freezer() under rcu read lock instead of task_lock(). This makes the state dereferencing racy against task moving to another cgroup; however, it was already racy without this change as ->state dereference wasn't synchronized. This will be later dealt with using attach hooks. * freezer->state is now set before trying to push tasks into the target state. -v2: Oleg pointed out that freeze_change_state() was setting freeze->state incorrectly to CGROUP_FROZEN instead of CGROUP_FREEZING. Fixed. -v3: Matt pointed out that setting CGROUP_FROZEN used to always invoke try_to_freeze_cgroup() regardless of the current state. Patch updated such that the actual freeze/thaw operations are always performed on invocation. This shouldn't make any difference unless something is broken. Signed-off-by: Tejun Heo Acked-by: Paul Menage Cc: Li Zefan Cc: Oleg Nesterov --- include/linux/freezer.h | 6 +++--- kernel/cgroup_freezer.c | 40 +++++++++++++--------------------------- kernel/power/process.c | 2 +- 3 files changed, 17 insertions(+), 31 deletions(-) diff --git a/include/linux/freezer.h b/include/linux/freezer.h index 93f411a52872..b2b4abc5a739 100644 --- a/include/linux/freezer.h +++ b/include/linux/freezer.h @@ -63,11 +63,11 @@ static inline bool try_to_freeze(void) extern bool freeze_task(struct task_struct *p, bool sig_only); #ifdef CONFIG_CGROUP_FREEZER -extern int cgroup_freezing_or_frozen(struct task_struct *task); +extern bool cgroup_freezing(struct task_struct *task); #else /* !CONFIG_CGROUP_FREEZER */ -static inline int cgroup_freezing_or_frozen(struct task_struct *task) +static inline bool cgroup_freezing(struct task_struct *task) { - return 0; + return false; } #endif /* !CONFIG_CGROUP_FREEZER */ diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c index cd27b0825560..e6a1b8d1b8bc 100644 --- a/kernel/cgroup_freezer.c +++ b/kernel/cgroup_freezer.c @@ -48,19 +48,17 @@ static inline struct freezer *task_freezer(struct task_struct *task) struct freezer, css); } -static inline int __cgroup_freezing_or_frozen(struct task_struct *task) +bool cgroup_freezing(struct task_struct *task) { - enum freezer_state state = task_freezer(task)->state; - return (state == CGROUP_FREEZING) || (state == CGROUP_FROZEN); -} + enum freezer_state state; + bool ret; -int cgroup_freezing_or_frozen(struct task_struct *task) -{ - int result; - task_lock(task); - result = __cgroup_freezing_or_frozen(task); - task_unlock(task); - return result; + rcu_read_lock(); + state = task_freezer(task)->state; + ret = state == CGROUP_FREEZING || state == CGROUP_FROZEN; + rcu_read_unlock(); + + return ret; } /* @@ -102,9 +100,6 @@ struct cgroup_subsys freezer_subsys; * freezer_can_attach(): * cgroup_mutex (held by caller of can_attach) * - * cgroup_freezing_or_frozen(): - * task->alloc_lock (to get task's cgroup) - * * freezer_fork() (preserving fork() performance means can't take cgroup_mutex): * freezer->lock * sighand->siglock (if the cgroup is freezing) @@ -177,13 +172,7 @@ static int freezer_can_attach(struct cgroup_subsys *ss, static int freezer_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk) { - rcu_read_lock(); - if (__cgroup_freezing_or_frozen(tsk)) { - rcu_read_unlock(); - return -EBUSY; - } - rcu_read_unlock(); - return 0; + return cgroup_freezing(tsk) ? -EBUSY : 0; } static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task) @@ -279,7 +268,6 @@ static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) struct task_struct *task; unsigned int num_cant_freeze_now = 0; - freezer->state = CGROUP_FREEZING; cgroup_iter_start(cgroup, &it); while ((task = cgroup_iter_next(cgroup, &it))) { if (!freeze_task(task, true)) @@ -303,8 +291,6 @@ static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) while ((task = cgroup_iter_next(cgroup, &it))) __thaw_task(task); cgroup_iter_end(cgroup, &it); - - freezer->state = CGROUP_THAWED; } static int freezer_change_state(struct cgroup *cgroup, @@ -318,20 +304,20 @@ static int freezer_change_state(struct cgroup *cgroup, spin_lock_irq(&freezer->lock); update_if_frozen(cgroup, freezer); - if (goal_state == freezer->state) - goto out; switch (goal_state) { case CGROUP_THAWED: + freezer->state = CGROUP_THAWED; unfreeze_cgroup(cgroup, freezer); break; case CGROUP_FROZEN: + freezer->state = CGROUP_FREEZING; retval = try_to_freeze_cgroup(cgroup, freezer); break; default: BUG(); } -out: + spin_unlock_irq(&freezer->lock); return retval; diff --git a/kernel/power/process.c b/kernel/power/process.c index ce643838a00c..9f6f5c755cfa 100644 --- a/kernel/power/process.c +++ b/kernel/power/process.c @@ -170,7 +170,7 @@ void thaw_processes(void) read_lock(&tasklist_lock); do_each_thread(g, p) { - if (cgroup_freezing_or_frozen(p)) + if (cgroup_freezing(p)) continue; __thaw_task(p); From a3201227f803ad7fd43180c5195dbe5a2bf998aa Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:25 -0800 Subject: [PATCH 14/24] freezer: make freezing() test freeze conditions in effect instead of TIF_FREEZE Using TIF_FREEZE for freezing worked when there was only single freezing condition (the PM one); however, now there is also the cgroup_freezer and single bit flag is getting clumsy. thaw_processes() is already testing whether cgroup freezing in in effect to avoid thawing tasks which were frozen by both PM and cgroup freezers. This is racy (nothing prevents race against cgroup freezing) and fragile. A much simpler way is to test actual freeze conditions from freezing() - ie. directly test whether PM or cgroup freezing is in effect. This patch adds variables to indicate whether and what type of freezing conditions are in effect and reimplements freezing() such that it directly tests whether any of the two freezing conditions is active and the task should freeze. On fast path, freezing() is still very cheap - it only tests system_freezing_cnt. This makes the clumsy dancing aroung TIF_FREEZE unnecessary and freeze/thaw operations more usual - updating state variables for the new state and nudging target tasks so that they notice the new state and comply. As long as the nudging happens after state update, it's race-free. * This allows use of freezing() in freeze_task(). Replace the open coded tests with freezing(). * p != current test is added to warning printing conditions in try_to_freeze_tasks() failure path. This is necessary as freezing() is now true for the task which initiated freezing too. -v2: Oleg pointed out that re-freezing FROZEN cgroup could increment system_freezing_cnt. Fixed. Signed-off-by: Tejun Heo Acked-by: Paul Menage (for the cgroup portions) --- include/linux/freezer.h | 33 ++++++++-------------- kernel/cgroup_freezer.c | 10 ++++++- kernel/fork.c | 1 - kernel/freezer.c | 62 ++++++++++++++++++++++++++--------------- kernel/power/process.c | 15 +++++++--- 5 files changed, 72 insertions(+), 49 deletions(-) diff --git a/include/linux/freezer.h b/include/linux/freezer.h index b2b4abc5a739..8e29f2b7ce11 100644 --- a/include/linux/freezer.h +++ b/include/linux/freezer.h @@ -5,8 +5,13 @@ #include #include +#include #ifdef CONFIG_FREEZER +extern atomic_t system_freezing_cnt; /* nr of freezing conds in effect */ +extern bool pm_freezing; /* PM freezing in effect */ +extern bool pm_nosig_freezing; /* PM nosig freezing in effect */ + /* * Check if a process has been frozen */ @@ -15,28 +20,16 @@ static inline int frozen(struct task_struct *p) return p->flags & PF_FROZEN; } +extern bool freezing_slow_path(struct task_struct *p); + /* * Check if there is a request to freeze a process */ -static inline int freezing(struct task_struct *p) +static inline bool freezing(struct task_struct *p) { - return test_tsk_thread_flag(p, TIF_FREEZE); -} - -/* - * Request that a process be frozen - */ -static inline void set_freeze_flag(struct task_struct *p) -{ - set_tsk_thread_flag(p, TIF_FREEZE); -} - -/* - * Sometimes we may need to cancel the previous 'freeze' request - */ -static inline void clear_freeze_flag(struct task_struct *p) -{ - clear_tsk_thread_flag(p, TIF_FREEZE); + if (likely(!atomic_read(&system_freezing_cnt))) + return false; + return freezing_slow_path(p); } static inline bool should_send_signal(struct task_struct *p) @@ -174,9 +167,7 @@ static inline void set_freezable_with_signal(void) }) #else /* !CONFIG_FREEZER */ static inline int frozen(struct task_struct *p) { return 0; } -static inline int freezing(struct task_struct *p) { return 0; } -static inline void set_freeze_flag(struct task_struct *p) {} -static inline void clear_freeze_flag(struct task_struct *p) {} +static inline bool freezing(struct task_struct *p) { return false; } static inline bool __refrigerator(bool check_kthr_stop) { return false; } static inline int freeze_processes(void) { return -ENOSYS; } diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c index e6a1b8d1b8bc..2327ad11725f 100644 --- a/kernel/cgroup_freezer.c +++ b/kernel/cgroup_freezer.c @@ -145,7 +145,11 @@ static struct cgroup_subsys_state *freezer_create(struct cgroup_subsys *ss, static void freezer_destroy(struct cgroup_subsys *ss, struct cgroup *cgroup) { - kfree(cgroup_freezer(cgroup)); + struct freezer *freezer = cgroup_freezer(cgroup); + + if (freezer->state != CGROUP_THAWED) + atomic_dec(&system_freezing_cnt); + kfree(freezer); } /* @@ -307,10 +311,14 @@ static int freezer_change_state(struct cgroup *cgroup, switch (goal_state) { case CGROUP_THAWED: + if (freezer->state != CGROUP_THAWED) + atomic_dec(&system_freezing_cnt); freezer->state = CGROUP_THAWED; unfreeze_cgroup(cgroup, freezer); break; case CGROUP_FROZEN: + if (freezer->state == CGROUP_THAWED) + atomic_inc(&system_freezing_cnt); freezer->state = CGROUP_FREEZING; retval = try_to_freeze_cgroup(cgroup, freezer); break; diff --git a/kernel/fork.c b/kernel/fork.c index ba0d17261329..d53316e88d9d 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -997,7 +997,6 @@ static void copy_flags(unsigned long clone_flags, struct task_struct *p) new_flags |= PF_FORKNOEXEC; new_flags |= PF_STARTING; p->flags = new_flags; - clear_freeze_flag(p); } SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr) diff --git a/kernel/freezer.c b/kernel/freezer.c index 11e32d419dec..f53cd5aa5b2e 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -11,9 +11,41 @@ #include #include +/* total number of freezing conditions in effect */ +atomic_t system_freezing_cnt = ATOMIC_INIT(0); +EXPORT_SYMBOL(system_freezing_cnt); + +/* indicate whether PM freezing is in effect, protected by pm_mutex */ +bool pm_freezing; +bool pm_nosig_freezing; + /* protects freezing and frozen transitions */ static DEFINE_SPINLOCK(freezer_lock); +/** + * freezing_slow_path - slow path for testing whether a task needs to be frozen + * @p: task to be tested + * + * This function is called by freezing() if system_freezing_cnt isn't zero + * and tests whether @p needs to enter and stay in frozen state. Can be + * called under any context. The freezers are responsible for ensuring the + * target tasks see the updated state. + */ +bool freezing_slow_path(struct task_struct *p) +{ + if (p->flags & PF_NOFREEZE) + return false; + + if (pm_nosig_freezing || cgroup_freezing(p)) + return true; + + if (pm_freezing && !(p->flags & PF_FREEZER_NOSIG)) + return true; + + return false; +} +EXPORT_SYMBOL(freezing_slow_path); + /* Refrigerator is place where frozen processes are stored :-). */ bool __refrigerator(bool check_kthr_stop) { @@ -23,17 +55,11 @@ bool __refrigerator(bool check_kthr_stop) long save; /* - * Enter FROZEN. If NOFREEZE, schedule immediate thawing by - * clearing freezing. + * No point in checking freezing() again - the caller already did. + * Proceed to enter FROZEN. */ spin_lock_irq(&freezer_lock); repeat: - if (!freezing(current)) { - spin_unlock_irq(&freezer_lock); - return was_frozen; - } - if (current->flags & PF_NOFREEZE) - clear_freeze_flag(current); current->flags |= PF_FROZEN; spin_unlock_irq(&freezer_lock); @@ -99,18 +125,12 @@ static void fake_signal_wake_up(struct task_struct *p) bool freeze_task(struct task_struct *p, bool sig_only) { unsigned long flags; - bool ret = false; spin_lock_irqsave(&freezer_lock, flags); - - if ((p->flags & PF_NOFREEZE) || - (sig_only && !should_send_signal(p))) - goto out_unlock; - - if (frozen(p)) - goto out_unlock; - - set_freeze_flag(p); + if (!freezing(p) || frozen(p)) { + spin_unlock_irqrestore(&freezer_lock, flags); + return false; + } if (should_send_signal(p)) { fake_signal_wake_up(p); @@ -123,10 +143,9 @@ bool freeze_task(struct task_struct *p, bool sig_only) } else { wake_up_state(p, TASK_INTERRUPTIBLE); } - ret = true; -out_unlock: + spin_unlock_irqrestore(&freezer_lock, flags); - return ret; + return true; } void __thaw_task(struct task_struct *p) @@ -143,7 +162,6 @@ void __thaw_task(struct task_struct *p) * avoid leaving dangling TIF_SIGPENDING behind. */ spin_lock_irqsave(&freezer_lock, flags); - clear_freeze_flag(p); if (frozen(p)) { wake_up_process(p); } else { diff --git a/kernel/power/process.c b/kernel/power/process.c index 9f6f5c755cfa..0beb51e1dec9 100644 --- a/kernel/power/process.c +++ b/kernel/power/process.c @@ -101,7 +101,7 @@ static int try_to_freeze_tasks(bool sig_only) read_lock(&tasklist_lock); do_each_thread(g, p) { if (!wakeup && !freezer_should_skip(p) && - freezing(p) && !frozen(p)) + p != current && freezing(p) && !frozen(p)) sched_show_task(p); } while_each_thread(g, p); read_unlock(&tasklist_lock); @@ -122,7 +122,11 @@ int freeze_processes(void) { int error; + if (!pm_freezing) + atomic_inc(&system_freezing_cnt); + printk("Freezing user space processes ... "); + pm_freezing = true; error = try_to_freeze_tasks(true); if (!error) { printk("done."); @@ -146,6 +150,7 @@ int freeze_kernel_threads(void) int error; printk("Freezing remaining freezable tasks ... "); + pm_nosig_freezing = true; error = try_to_freeze_tasks(false); if (!error) printk("done."); @@ -162,6 +167,11 @@ void thaw_processes(void) { struct task_struct *g, *p; + if (pm_freezing) + atomic_dec(&system_freezing_cnt); + pm_freezing = false; + pm_nosig_freezing = false; + oom_killer_enable(); printk("Restarting tasks ... "); @@ -170,9 +180,6 @@ void thaw_processes(void) read_lock(&tasklist_lock); do_each_thread(g, p) { - if (cgroup_freezing(p)) - continue; - __thaw_task(p); } while_each_thread(g, p); read_unlock(&tasklist_lock); From d88e4cb67197d007fb778d62fe17360e970d5bfa Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:25 -0800 Subject: [PATCH 15/24] freezer: remove now unused TIF_FREEZE Signed-off-by: Tejun Heo Cc: Arnd Bergmann Cc: linux-arch@vger.kernel.org --- arch/alpha/include/asm/thread_info.h | 2 -- arch/arm/include/asm/thread_info.h | 2 -- arch/avr32/include/asm/thread_info.h | 2 -- arch/blackfin/include/asm/thread_info.h | 2 -- arch/cris/include/asm/thread_info.h | 2 -- arch/frv/include/asm/thread_info.h | 2 -- arch/h8300/include/asm/thread_info.h | 2 -- arch/ia64/include/asm/thread_info.h | 2 -- arch/m32r/include/asm/thread_info.h | 2 -- arch/m68k/include/asm/thread_info.h | 1 - arch/microblaze/include/asm/thread_info.h | 2 -- arch/mips/include/asm/thread_info.h | 2 -- arch/mn10300/include/asm/thread_info.h | 2 -- arch/parisc/include/asm/thread_info.h | 2 -- arch/powerpc/include/asm/thread_info.h | 2 -- arch/s390/include/asm/thread_info.h | 2 -- arch/sh/include/asm/thread_info.h | 2 -- arch/sparc/include/asm/thread_info_32.h | 2 -- arch/sparc/include/asm/thread_info_64.h | 2 -- arch/um/include/asm/thread_info.h | 2 -- arch/unicore32/include/asm/thread_info.h | 2 -- arch/x86/include/asm/thread_info.h | 2 -- arch/xtensa/include/asm/thread_info.h | 2 -- 23 files changed, 45 deletions(-) diff --git a/arch/alpha/include/asm/thread_info.h b/arch/alpha/include/asm/thread_info.h index ff73db022342..28335bd40e40 100644 --- a/arch/alpha/include/asm/thread_info.h +++ b/arch/alpha/include/asm/thread_info.h @@ -79,7 +79,6 @@ register struct thread_info *__current_thread_info __asm__("$8"); #define TIF_UAC_SIGBUS 12 /* ! userspace part of 'osf_sysinfo' */ #define TIF_MEMDIE 13 /* is terminating due to OOM killer */ #define TIF_RESTORE_SIGMASK 14 /* restore signal mask in do_signal */ -#define TIF_FREEZE 16 /* is freezing for suspend */ #define _TIF_SYSCALL_TRACE (1< Date: Mon, 21 Nov 2011 12:32:25 -0800 Subject: [PATCH 16/24] freezer: remove should_send_signal() and update frozen() should_send_signal() is only used in freezer.c. Exporting them only increases chance of abuse. Open code the two users and remove it. Update frozen() to return bool. Signed-off-by: Tejun Heo --- include/linux/freezer.h | 9 ++------- kernel/freezer.c | 2 +- 2 files changed, 3 insertions(+), 8 deletions(-) diff --git a/include/linux/freezer.h b/include/linux/freezer.h index 8e29f2b7ce11..3d50913d39d0 100644 --- a/include/linux/freezer.h +++ b/include/linux/freezer.h @@ -15,7 +15,7 @@ extern bool pm_nosig_freezing; /* PM nosig freezing in effect */ /* * Check if a process has been frozen */ -static inline int frozen(struct task_struct *p) +static inline bool frozen(struct task_struct *p) { return p->flags & PF_FROZEN; } @@ -32,11 +32,6 @@ static inline bool freezing(struct task_struct *p) return freezing_slow_path(p); } -static inline bool should_send_signal(struct task_struct *p) -{ - return !(p->flags & PF_FREEZER_NOSIG); -} - /* Takes and releases task alloc lock using task_lock() */ extern void __thaw_task(struct task_struct *t); @@ -166,7 +161,7 @@ static inline void set_freezable_with_signal(void) __retval; \ }) #else /* !CONFIG_FREEZER */ -static inline int frozen(struct task_struct *p) { return 0; } +static inline bool frozen(struct task_struct *p) { return false; } static inline bool freezing(struct task_struct *p) { return false; } static inline bool __refrigerator(bool check_kthr_stop) { return false; } diff --git a/kernel/freezer.c b/kernel/freezer.c index f53cd5aa5b2e..95a123844241 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -132,7 +132,7 @@ bool freeze_task(struct task_struct *p, bool sig_only) return false; } - if (should_send_signal(p)) { + if (!(p->flags & PF_FREEZER_NOSIG)) { fake_signal_wake_up(p); /* * fake_signal_wake_up() goes through p's scheduler From 96ee6d8539c9fc6742908d85eb9723abb5c91854 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:25 -0800 Subject: [PATCH 17/24] freezer: fix set_freezable[_with_signal]() race A kthread doing set_freezable*() may race with on-going PM freeze and the freezer might think all tasks are frozen while the new freezable kthread is merrily proceeding to execute code paths which aren't supposed to be executing during PM freeze. Reimplement set_freezable[_with_signal]() using __set_freezable() such that freezable PF flags are modified under freezer_lock and try_to_freeze() is called afterwards. This eliminates race condition against freezing. Note: Separated out from larger patch to resolve fix order dependency Oleg pointed out. Signed-off-by: Tejun Heo Cc: Oleg Nesterov --- include/linux/freezer.h | 9 +++++---- kernel/freezer.c | 25 +++++++++++++++++++++++++ 2 files changed, 30 insertions(+), 4 deletions(-) diff --git a/include/linux/freezer.h b/include/linux/freezer.h index 3d50913d39d0..a0f1b3a3604f 100644 --- a/include/linux/freezer.h +++ b/include/linux/freezer.h @@ -49,6 +49,7 @@ static inline bool try_to_freeze(void) } extern bool freeze_task(struct task_struct *p, bool sig_only); +extern bool __set_freezable(bool with_signal); #ifdef CONFIG_CGROUP_FREEZER extern bool cgroup_freezing(struct task_struct *task); @@ -106,18 +107,18 @@ static inline int freezer_should_skip(struct task_struct *p) /* * Tell the freezer that the current task should be frozen by it */ -static inline void set_freezable(void) +static inline bool set_freezable(void) { - current->flags &= ~PF_NOFREEZE; + return __set_freezable(false); } /* * Tell the freezer that the current task should be frozen by it and that it * should send a fake signal to the task to freeze it. */ -static inline void set_freezable_with_signal(void) +static inline bool set_freezable_with_signal(void) { - current->flags &= ~(PF_NOFREEZE | PF_FREEZER_NOSIG); + return __set_freezable(true); } /* diff --git a/kernel/freezer.c b/kernel/freezer.c index 95a123844241..b1e7a7b3d2cd 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -171,3 +171,28 @@ void __thaw_task(struct task_struct *p) } spin_unlock_irqrestore(&freezer_lock, flags); } + +/** + * __set_freezable - make %current freezable + * @with_signal: do we want %TIF_SIGPENDING for notification too? + * + * Mark %current freezable and enter refrigerator if necessary. + */ +bool __set_freezable(bool with_signal) +{ + might_sleep(); + + /* + * Modify flags while holding freezer_lock. This ensures the + * freezer notices that we aren't frozen yet or the freezing + * condition is visible to try_to_freeze() below. + */ + spin_lock_irq(&freezer_lock); + current->flags &= ~PF_NOFREEZE; + if (with_signal) + current->flags &= ~PF_FREEZER_NOSIG; + spin_unlock_irq(&freezer_lock); + + return try_to_freeze(); +} +EXPORT_SYMBOL(__set_freezable); From 5ece3eae4cdb968c269e0bc7e2c0e2b223552025 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:26 -0800 Subject: [PATCH 18/24] freezer: restructure __refrigerator() If another freeze happens before all tasks leave FROZEN state after being thawed, the freezer can see the existing FROZEN and consider the tasks to be frozen but they can clear FROZEN without checking the new freezing(). Oleg suggested restructuring __refrigerator() such that there's single condition check section inside freezer_lock and sigpending is cleared afterwards, which fixes the problem and simplifies the code. Restructure accordingly. -v2: Frozen loop exited without releasing freezer_lock. Fixed. Signed-off-by: Tejun Heo Reported-by: Oleg Nesterov Acked-by: Oleg Nesterov Cc: "Rafael J. Wysocki" --- kernel/freezer.c | 32 +++++++++++--------------------- 1 file changed, 11 insertions(+), 21 deletions(-) diff --git a/kernel/freezer.c b/kernel/freezer.c index b1e7a7b3d2cd..c3496c6a91b2 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -52,39 +52,29 @@ bool __refrigerator(bool check_kthr_stop) /* Hmm, should we be allowed to suspend when there are realtime processes around? */ bool was_frozen = false; - long save; + long save = current->state; - /* - * No point in checking freezing() again - the caller already did. - * Proceed to enter FROZEN. - */ - spin_lock_irq(&freezer_lock); -repeat: - current->flags |= PF_FROZEN; - spin_unlock_irq(&freezer_lock); - - save = current->state; pr_debug("%s entered refrigerator\n", current->comm); - spin_lock_irq(¤t->sighand->siglock); - recalc_sigpending(); /* We sent fake signal, clean it up */ - spin_unlock_irq(¤t->sighand->siglock); - for (;;) { set_current_state(TASK_UNINTERRUPTIBLE); + + spin_lock_irq(&freezer_lock); + current->flags |= PF_FROZEN; if (!freezing(current) || (check_kthr_stop && kthread_should_stop())) + current->flags &= ~PF_FROZEN; + spin_unlock_irq(&freezer_lock); + + if (!(current->flags & PF_FROZEN)) break; was_frozen = true; schedule(); } - /* leave FROZEN */ - spin_lock_irq(&freezer_lock); - if (freezing(current)) - goto repeat; - current->flags &= ~PF_FROZEN; - spin_unlock_irq(&freezer_lock); + spin_lock_irq(¤t->sighand->siglock); + recalc_sigpending(); /* We sent fake signal, clean it up */ + spin_unlock_irq(¤t->sighand->siglock); pr_debug("%s left refrigerator\n", current->comm); From 37ad8aca94a1da2112a7c56151390914e80d1113 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:26 -0800 Subject: [PATCH 19/24] freezer: use lock_task_sighand() in fake_signal_wake_up() cgroup_freezer calls freeze_task() without holding tasklist_lock and, if the task is exiting, its ->sighand may be gone by the time fake_signal_wake_up() is called. Use lock_task_sighand() instead of accessing ->sighand directly. Signed-off-by: Tejun Heo Reported-by: Oleg Nesterov Acked-by: Oleg Nesterov Cc: "Rafael J. Wysocki" Cc: Paul Menage --- kernel/freezer.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/kernel/freezer.c b/kernel/freezer.c index c3496c6a91b2..389549f0a94e 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -93,9 +93,10 @@ static void fake_signal_wake_up(struct task_struct *p) { unsigned long flags; - spin_lock_irqsave(&p->sighand->siglock, flags); - signal_wake_up(p, 0); - spin_unlock_irqrestore(&p->sighand->siglock, flags); + if (lock_task_sighand(p, &flags)) { + signal_wake_up(p, 0); + unlock_task_sighand(p, &flags); + } } /** From 839e3407d90a810318d17c17ceb3d5928a910704 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:26 -0800 Subject: [PATCH 20/24] freezer: remove unused @sig_only from freeze_task() After "freezer: make freezing() test freeze conditions in effect instead of TIF_FREEZE", freezing() returns authoritative answer on whether the current task should freeze or not and freeze_task() doesn't need or use @sig_only. Remove it. While at it, rewrite function comment for freeze_task() and rename @sig_only to @user_only in try_to_freeze_tasks(). This patch doesn't cause any functional change. Signed-off-by: Tejun Heo Acked-by: Oleg Nesterov --- include/linux/freezer.h | 2 +- kernel/cgroup_freezer.c | 4 ++-- kernel/freezer.c | 21 +++++++++------------ kernel/power/process.c | 8 ++++---- 4 files changed, 16 insertions(+), 19 deletions(-) diff --git a/include/linux/freezer.h b/include/linux/freezer.h index a0f1b3a3604f..a28842e588f4 100644 --- a/include/linux/freezer.h +++ b/include/linux/freezer.h @@ -48,7 +48,7 @@ static inline bool try_to_freeze(void) return __refrigerator(false); } -extern bool freeze_task(struct task_struct *p, bool sig_only); +extern bool freeze_task(struct task_struct *p); extern bool __set_freezable(bool with_signal); #ifdef CONFIG_CGROUP_FREEZER diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c index 2327ad11725f..e411a60cc2c8 100644 --- a/kernel/cgroup_freezer.c +++ b/kernel/cgroup_freezer.c @@ -206,7 +206,7 @@ static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task) /* Locking avoids race with FREEZING -> THAWED transitions. */ if (freezer->state == CGROUP_FREEZING) - freeze_task(task, true); + freeze_task(task); spin_unlock_irq(&freezer->lock); } @@ -274,7 +274,7 @@ static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) cgroup_iter_start(cgroup, &it); while ((task = cgroup_iter_next(cgroup, &it))) { - if (!freeze_task(task, true)) + if (!freeze_task(task)) continue; if (frozen(task)) continue; diff --git a/kernel/freezer.c b/kernel/freezer.c index 389549f0a94e..2589a61de44c 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -100,20 +100,17 @@ static void fake_signal_wake_up(struct task_struct *p) } /** - * freeze_task - send a freeze request to given task - * @p: task to send the request to - * @sig_only: if set, the request will only be sent if the task has the - * PF_FREEZER_NOSIG flag unset - * Return value: 'false', if @sig_only is set and the task has - * PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise + * freeze_task - send a freeze request to given task + * @p: task to send the request to * - * The freeze request is sent by setting the tasks's TIF_FREEZE flag and - * either sending a fake signal to it or waking it up, depending on whether - * or not it has PF_FREEZER_NOSIG set. If @sig_only is set and the task - * has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its - * TIF_FREEZE flag will not be set. + * If @p is freezing, the freeze request is sent by setting %TIF_FREEZE + * flag and either sending a fake signal to it or waking it up, depending + * on whether it has %PF_FREEZER_NOSIG set. + * + * RETURNS: + * %false, if @p is not freezing or already frozen; %true, otherwise */ -bool freeze_task(struct task_struct *p, bool sig_only) +bool freeze_task(struct task_struct *p) { unsigned long flags; diff --git a/kernel/power/process.c b/kernel/power/process.c index 0beb51e1dec9..77274c9ba2f1 100644 --- a/kernel/power/process.c +++ b/kernel/power/process.c @@ -22,7 +22,7 @@ */ #define TIMEOUT (20 * HZ) -static int try_to_freeze_tasks(bool sig_only) +static int try_to_freeze_tasks(bool user_only) { struct task_struct *g, *p; unsigned long end_time; @@ -37,14 +37,14 @@ static int try_to_freeze_tasks(bool sig_only) end_time = jiffies + TIMEOUT; - if (!sig_only) + if (!user_only) freeze_workqueues_begin(); while (true) { todo = 0; read_lock(&tasklist_lock); do_each_thread(g, p) { - if (p == current || !freeze_task(p, sig_only)) + if (p == current || !freeze_task(p)) continue; /* @@ -65,7 +65,7 @@ static int try_to_freeze_tasks(bool sig_only) } while_each_thread(g, p); read_unlock(&tasklist_lock); - if (!sig_only) { + if (!user_only) { wq_busy = freeze_workqueues_busy(); todo += wq_busy; } From ec012476af73a1a8a82565a915e9b48c2e337878 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:26 -0800 Subject: [PATCH 21/24] usb_storage: don't use set_freezable_with_signal() The current implementation of set_freezable_with_signal() is buggy and tricky to get right. usb-storage is the only user and its use can be avoided trivially. All usb-storage wants is to be able to sleep with timeout and get woken up if freezing() becomes true. This can be trivially implemented by doing interruptible wait w/ freezing() included in the wait condition. There's no reason to use set_freezable_with_signal(). Perform interruptible wait on freezing() instead of using set_freezable_with_signal(), which is scheduled for removal. Signed-off-by: Tejun Heo Cc: Oleg Nesterov Cc: "Rafael J. Wysocki" Cc: Seth Forshee Cc: Alan Stern Cc: Greg Kroah-Hartman --- drivers/usb/storage/usb.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/drivers/usb/storage/usb.c b/drivers/usb/storage/usb.c index c325e69415a1..aa84b3d77274 100644 --- a/drivers/usb/storage/usb.c +++ b/drivers/usb/storage/usb.c @@ -831,7 +831,8 @@ static int usb_stor_scan_thread(void * __us) dev_dbg(dev, "device found\n"); - set_freezable_with_signal(); + set_freezable(); + /* * Wait for the timeout to expire or for a disconnect * @@ -839,16 +840,16 @@ static int usb_stor_scan_thread(void * __us) * fail to freeze, but we can't be non-freezable either. Nor can * khubd freeze while waiting for scanning to complete as it may * hold the device lock, causing a hang when suspending devices. - * So we request a fake signal when freezing and use - * interruptible sleep to kick us out of our wait early when - * freezing happens. + * So instead of using wait_event_freezable(), explicitly test + * for (DONT_SCAN || freezing) in interruptible wait and proceed + * if any of DONT_SCAN, freezing or timeout has happened. */ if (delay_use > 0) { dev_dbg(dev, "waiting for device to settle " "before scanning\n"); wait_event_interruptible_timeout(us->delay_wait, - test_bit(US_FLIDX_DONT_SCAN, &us->dflags), - delay_use * HZ); + test_bit(US_FLIDX_DONT_SCAN, &us->dflags) || + freezing(current), delay_use * HZ); } /* If the device is still connected, perform the scanning */ From adfa543e7314b36ac55a40019977de6e47946dd7 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Wed, 23 Nov 2011 09:28:16 -0800 Subject: [PATCH 22/24] dmatest: don't use set_freezable_with_signal() Commit 981ed70d8e (dmatest: make dmatest threads freezable) made dmatest kthread use set_freezable_with_signal(); however, the interface is scheduled to be removed in the next merge window. The problem is that unlike userland tasks there's no default place which handles signal pending state and it isn't clear who owns and/or is responsible for clearing TIF_SIGPENDING. For example, in the current code, try_to_freeze() clears TIF_SIGPENDING but it isn't sure whether it actually owns the TIF_SIGPENDING nor is it race-free - ie. the task may continue to run with TIF_SIGPENDING set after the freezable section. Unfortunately, we don't have wait_for_completion_freezable_timeout(). This patch open codes it and uses wait_event_freezable_timeout() instead and removes timeout reloading - wait_event_freezable_timeout() won't return across freezing events (currently racy but fix scheduled) and timer doesn't decrement while the task is in freezer. Although this does lose timer-reset-over-freezing, given that timeout is supposed to be long enough and failure to finish inside is considered irrecoverable, I don't think this is worth the complexity. While at it, move completion to outer scope and explain that we're ignoring dangling pointer problem after timeout. This should give slightly better chance at avoiding oops after timeout. Signed-off-by: Tejun Heo Acked-by: Dan Williams Cc: Guennadi Liakhovetski Cc: Nicolas Ferre --- drivers/dma/dmatest.c | 46 +++++++++++++++++++++++++------------------ 1 file changed, 27 insertions(+), 19 deletions(-) diff --git a/drivers/dma/dmatest.c b/drivers/dma/dmatest.c index eb1d8641cf5c..2b8661b54eaf 100644 --- a/drivers/dma/dmatest.c +++ b/drivers/dma/dmatest.c @@ -214,9 +214,18 @@ static unsigned int dmatest_verify(u8 **bufs, unsigned int start, return error_count; } -static void dmatest_callback(void *completion) +/* poor man's completion - we want to use wait_event_freezable() on it */ +struct dmatest_done { + bool done; + wait_queue_head_t *wait; +}; + +static void dmatest_callback(void *arg) { - complete(completion); + struct dmatest_done *done = arg; + + done->done = true; + wake_up_all(done->wait); } /* @@ -235,7 +244,9 @@ static void dmatest_callback(void *completion) */ static int dmatest_func(void *data) { + DECLARE_WAIT_QUEUE_HEAD_ONSTACK(done_wait); struct dmatest_thread *thread = data; + struct dmatest_done done = { .wait = &done_wait }; struct dma_chan *chan; const char *thread_name; unsigned int src_off, dst_off, len; @@ -252,7 +263,7 @@ static int dmatest_func(void *data) int i; thread_name = current->comm; - set_freezable_with_signal(); + set_freezable(); ret = -ENOMEM; @@ -306,9 +317,6 @@ static int dmatest_func(void *data) struct dma_async_tx_descriptor *tx = NULL; dma_addr_t dma_srcs[src_cnt]; dma_addr_t dma_dsts[dst_cnt]; - struct completion cmp; - unsigned long start, tmo, end = 0 /* compiler... */; - bool reload = true; u8 align = 0; total_tests++; @@ -391,9 +399,9 @@ static int dmatest_func(void *data) continue; } - init_completion(&cmp); + done.done = false; tx->callback = dmatest_callback; - tx->callback_param = &cmp; + tx->callback_param = &done; cookie = tx->tx_submit(tx); if (dma_submit_error(cookie)) { @@ -407,20 +415,20 @@ static int dmatest_func(void *data) } dma_async_issue_pending(chan); - do { - start = jiffies; - if (reload) - end = start + msecs_to_jiffies(timeout); - else if (end <= start) - end = start + 1; - tmo = wait_for_completion_interruptible_timeout(&cmp, - end - start); - reload = try_to_freeze(); - } while (tmo == -ERESTARTSYS); + wait_event_freezable_timeout(done_wait, done.done, + msecs_to_jiffies(timeout)); status = dma_async_is_tx_complete(chan, cookie, NULL, NULL); - if (tmo == 0) { + if (!done.done) { + /* + * We're leaving the timed out dma operation with + * dangling pointer to done_wait. To make this + * correct, we'll need to allocate wait_done for + * each test iteration and perform "who's gonna + * free it this time?" dancing. For now, just + * leave it dangling. + */ pr_warning("%s: #%u: test timed out\n", thread_name, total_tests - 1); failed_tests++; From 34b087e48367c252e343c2f8de65676a78af1e4a Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Wed, 23 Nov 2011 09:28:17 -0800 Subject: [PATCH 23/24] freezer: kill unused set_freezable_with_signal() There's no in-kernel user of set_freezable_with_signal() left. Mixing TIF_SIGPENDING with kernel threads can lead to nasty corner cases as kernel threads never travel signal delivery path on their own. e.g. the current implementation is buggy in the cancelation path of __thaw_task(). It calls recalc_sigpending_and_wake() in an attempt to clear TIF_SIGPENDING but the function never clears it regardless of sigpending state. This means that signallable freezable kthreads may continue executing with !freezing() && stuck TIF_SIGPENDING, which can be troublesome. This patch removes set_freezable_with_signal() along with PF_FREEZER_NOSIG and recalc_sigpending*() calls in freezer. User tasks get TIF_SIGPENDING, kernel tasks get woken up and the spurious sigpending is dealt with in the usual signal delivery path. Signed-off-by: Tejun Heo Acked-by: Oleg Nesterov --- include/linux/freezer.h | 20 +------------------- include/linux/sched.h | 1 - kernel/freezer.c | 27 ++++++--------------------- kernel/kthread.c | 2 +- 4 files changed, 8 insertions(+), 42 deletions(-) diff --git a/include/linux/freezer.h b/include/linux/freezer.h index a28842e588f4..a33550fc05c5 100644 --- a/include/linux/freezer.h +++ b/include/linux/freezer.h @@ -49,7 +49,7 @@ static inline bool try_to_freeze(void) } extern bool freeze_task(struct task_struct *p); -extern bool __set_freezable(bool with_signal); +extern bool set_freezable(void); #ifdef CONFIG_CGROUP_FREEZER extern bool cgroup_freezing(struct task_struct *task); @@ -104,23 +104,6 @@ static inline int freezer_should_skip(struct task_struct *p) return !!(p->flags & PF_FREEZER_SKIP); } -/* - * Tell the freezer that the current task should be frozen by it - */ -static inline bool set_freezable(void) -{ - return __set_freezable(false); -} - -/* - * Tell the freezer that the current task should be frozen by it and that it - * should send a fake signal to the task to freeze it. - */ -static inline bool set_freezable_with_signal(void) -{ - return __set_freezable(true); -} - /* * Freezer-friendly wrappers around wait_event_interruptible(), * wait_event_killable() and wait_event_interruptible_timeout(), originally @@ -176,7 +159,6 @@ static inline void freezer_do_not_count(void) {} static inline void freezer_count(void) {} static inline int freezer_should_skip(struct task_struct *p) { return 0; } static inline void set_freezable(void) {} -static inline void set_freezable_with_signal(void) {} #define wait_event_freezable(wq, condition) \ wait_event_interruptible(wq, condition) diff --git a/include/linux/sched.h b/include/linux/sched.h index d12bd03b688f..2f90470ad843 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1788,7 +1788,6 @@ extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t * #define PF_MEMPOLICY 0x10000000 /* Non-default NUMA mempolicy */ #define PF_MUTEX_TESTER 0x20000000 /* Thread belongs to the rt mutex tester */ #define PF_FREEZER_SKIP 0x40000000 /* Freezer should not count it as freezable */ -#define PF_FREEZER_NOSIG 0x80000000 /* Freezer won't send signals to it */ /* * Only the _current_ task can read/write to tsk->flags, but other diff --git a/kernel/freezer.c b/kernel/freezer.c index 2589a61de44c..9815b8d1eed5 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -39,7 +39,7 @@ bool freezing_slow_path(struct task_struct *p) if (pm_nosig_freezing || cgroup_freezing(p)) return true; - if (pm_freezing && !(p->flags & PF_FREEZER_NOSIG)) + if (pm_freezing && !(p->flags & PF_KTHREAD)) return true; return false; @@ -72,10 +72,6 @@ bool __refrigerator(bool check_kthr_stop) schedule(); } - spin_lock_irq(¤t->sighand->siglock); - recalc_sigpending(); /* We sent fake signal, clean it up */ - spin_unlock_irq(¤t->sighand->siglock); - pr_debug("%s left refrigerator\n", current->comm); /* @@ -120,7 +116,7 @@ bool freeze_task(struct task_struct *p) return false; } - if (!(p->flags & PF_FREEZER_NOSIG)) { + if (!(p->flags & PF_KTHREAD)) { fake_signal_wake_up(p); /* * fake_signal_wake_up() goes through p's scheduler @@ -145,28 +141,19 @@ void __thaw_task(struct task_struct *p) * be visible to @p as waking up implies wmb. Waking up inside * freezer_lock also prevents wakeups from leaking outside * refrigerator. - * - * If !FROZEN, @p hasn't reached refrigerator, recalc sigpending to - * avoid leaving dangling TIF_SIGPENDING behind. */ spin_lock_irqsave(&freezer_lock, flags); - if (frozen(p)) { + if (frozen(p)) wake_up_process(p); - } else { - spin_lock(&p->sighand->siglock); - recalc_sigpending_and_wake(p); - spin_unlock(&p->sighand->siglock); - } spin_unlock_irqrestore(&freezer_lock, flags); } /** - * __set_freezable - make %current freezable - * @with_signal: do we want %TIF_SIGPENDING for notification too? + * set_freezable - make %current freezable * * Mark %current freezable and enter refrigerator if necessary. */ -bool __set_freezable(bool with_signal) +bool set_freezable(void) { might_sleep(); @@ -177,10 +164,8 @@ bool __set_freezable(bool with_signal) */ spin_lock_irq(&freezer_lock); current->flags &= ~PF_NOFREEZE; - if (with_signal) - current->flags &= ~PF_FREEZER_NOSIG; spin_unlock_irq(&freezer_lock); return try_to_freeze(); } -EXPORT_SYMBOL(__set_freezable); +EXPORT_SYMBOL(set_freezable); diff --git a/kernel/kthread.c b/kernel/kthread.c index 1c36deaae2f1..3d3de633702e 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -282,7 +282,7 @@ int kthreadd(void *unused) set_cpus_allowed_ptr(tsk, cpu_all_mask); set_mems_allowed(node_states[N_HIGH_MEMORY]); - current->flags |= PF_NOFREEZE | PF_FREEZER_NOSIG; + current->flags |= PF_NOFREEZE; for (;;) { set_current_state(TASK_INTERRUPTIBLE); From 24b7ead3fb0bae267c2ee50898eb4c13aedd1e9f Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Wed, 23 Nov 2011 09:28:17 -0800 Subject: [PATCH 24/24] freezer: fix wait_event_freezable/__thaw_task races wait_event_freezable() and friends stop the waiting if try_to_freeze() fails. This is not right, we can race with __thaw_task() and in this case - wait_event_freezable() returns the wrong ERESTARTSYS - wait_event_freezable_timeout() can return the positive value while condition == F Change the code to always check __retval/condition before return. Note: with or without this patch the timeout logic looks strange, probably we should recalc timeout if try_to_freeze() returns T. Signed-off-by: Oleg Nesterov Acked-by: Tejun Heo --- include/linux/freezer.h | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) diff --git a/include/linux/freezer.h b/include/linux/freezer.h index a33550fc05c5..09570ac22be6 100644 --- a/include/linux/freezer.h +++ b/include/linux/freezer.h @@ -122,28 +122,30 @@ static inline int freezer_should_skip(struct task_struct *p) #define wait_event_freezable(wq, condition) \ ({ \ int __retval; \ - do { \ + for (;;) { \ __retval = wait_event_interruptible(wq, \ (condition) || freezing(current)); \ - if (__retval && !freezing(current)) \ + if (__retval || (condition)) \ break; \ - else if (!(condition)) \ - __retval = -ERESTARTSYS; \ - } while (try_to_freeze()); \ + try_to_freeze(); \ + } \ __retval; \ }) - #define wait_event_freezable_timeout(wq, condition, timeout) \ ({ \ long __retval = timeout; \ - do { \ + for (;;) { \ __retval = wait_event_interruptible_timeout(wq, \ (condition) || freezing(current), \ __retval); \ - } while (try_to_freeze()); \ + if (__retval <= 0 || (condition)) \ + break; \ + try_to_freeze(); \ + } \ __retval; \ }) + #else /* !CONFIG_FREEZER */ static inline bool frozen(struct task_struct *p) { return false; } static inline bool freezing(struct task_struct *p) { return false; }