Pull RCU changes for v3.4 from Ingo Molnar. The major features of this
series are:
- making RCU more aggressive about entering dyntick-idle mode in order
to improve energy efficiency
- converting a few more call_rcu()s to kfree_rcu()s
- applying a number of rcutree fixes and cleanups to rcutiny
- removing CONFIG_SMP #ifdefs from treercu
- allowing RCU CPU stall times to be set via sysfs
- adding CPU-stall capability to rcutorture
- adding more RCU-abuse diagnostics
- updating documentation
- fixing yet more issues located by the still-ongoing top-to-bottom
inspection of RCU, this time with a special focus on the CPU-hotplug
code path.
* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (48 commits)
rcu: Stop spurious warnings from synchronize_sched_expedited
rcu: Hold off RCU_FAST_NO_HZ after timer posted
rcu: Eliminate softirq-mediated RCU_FAST_NO_HZ idle-entry loop
rcu: Add RCU_NONIDLE() for idle-loop RCU read-side critical sections
rcu: Allow nesting of rcu_idle_enter() and rcu_idle_exit()
rcu: Remove redundant check for rcu_head misalignment
PTR_ERR should be called before its argument is cleared.
rcu: Convert WARN_ON_ONCE() in rcu_lock_acquire() to lockdep
rcu: Trace only after NULL-pointer check
rcu: Call out dangers of expedited RCU primitives
rcu: Rework detection of use of RCU by offline CPUs
lockdep: Add CPU-idle/offline warning to lockdep-RCU splat
rcu: No interrupt disabling for rcu_prepare_for_idle()
rcu: Move synchronize_sched_expedited() to rcutree.c
rcu: Check for illegal use of RCU from offlined CPUs
rcu: Update stall-warning documentation
rcu: Add CPU-stall capability to rcutorture
rcu: Make documentation give more realistic rcutorture duration
rcutorture: Permit holding off CPU-hotplug operations during boot
rcu: Print scheduling-clock information on RCU CPU stall-warning messages
...
Pull core/locking changes for v3.4 from Ingo Molnar
* 'core-locking-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
futex: Simplify return logic
futex: Cover all PI opcodes with cmpxchg enabled check
CAP_SYS_ADMIN is already overloaded left and right, so to have more
fine-grained access control use CAP_SYS_RESOURCE here.
The CAP_SYS_RESOUCE is chosen because this prctl option allows a current
process to adjust some fields of memory map descriptor which rather
represents what the process owns: pointers to code, data, stack
segments, command line, auxiliary vector data and etc.
Suggested-by: Michael Kerrisk <mtk.manpages@gmail.com>
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul Bolle <pebolle@tiscali.nl>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Pull block fixes from Jens Axboe:
"Been sitting on this for a while, but lets get this out the door.
This fixes various important bugs for 3.3 final, along with a few more
trivial ones. Please pull!"
* 'for-linus' of git://git.kernel.dk/linux-block:
block: fix ioc leak in put_io_context
block, sx8: fix pointer math issue getting fw version
Block: use a freezable workqueue for disk-event polling
drivers/block/DAC960: fix -Wuninitialized warning
drivers/block/DAC960: fix DAC960_V2_IOCTL_Opcode_T -Wenum-compare warning
block: fix __blkdev_get and add_disk race condition
block: Fix setting bio flags in drivers (sd_dif/floppy)
block: Fix NULL pointer dereference in sd_revalidate_disk
block: exit_io_context() should call elevator_exit_icq_fn()
block: simplify ioc_release_fn()
block: replace icq->changed with icq->flags
This reverts commit 8f2f748b06.
It causes some odd regression that we have not figured out, and it's too
late in the -rc series to try to figure it out now.
As reported by Konstantin Khlebnikov, it causes consistent hangs on his
laptop (Thinkpad x220: 2x cores + HT). They can be avoided by adding
calls to "rebuild_sched_domains();" in cpuset_cpu_[in]active() for the
CPU_{ONLINE/DOWN_FAILED/DOWN_PREPARE}_FROZEN cases, but it's not at all
clear why, and it makes no sense.
Konstantin's config doesn't even have CONFIG_CPUSETS enabled, just to
make things even more interesting. So it's not the cpusets, it's just
the scheduling domains.
So until this is understood, revert.
Bisected-reported-and-tested-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Xommit ac5637611(genirq: Unmask oneshot irqs when thread was not woken)
fails to unmask when a !IRQ_ONESHOT threaded handler is handled by
handle_level_irq.
This happens because thread_mask is or'ed unconditionally in
irq_wake_thread(), but for !IRQ_ONESHOT interrupts never cleared. So
the check for !desc->thread_active fails and keeps the interrupt
disabled.
Keep the thread_mask zero for !IRQ_ONESHOT interrupts.
Document the thread_mask magic while at it.
Reported-and-tested-by: Sven Joachim <svenjoac@gmx.de>
Reported-and-tested-by: Stefan Lippers-Hollmann <s.l-h@gmx.de>
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
check_hung_uninterruptible_tasks()->rcu_lock_break() introduced by
"softlockup: check all tasks in hung_task" commit ce9dbe24 looks
absolutely wrong.
- rcu_lock_break() does put_task_struct(). If the task has exited
it is not safe to even read its ->state, nothing protects this
task_struct.
- The TASK_DEAD checks are wrong too. Contrary to the comment, we
can't use it to check if the task was unhashed. It can be unhashed
without TASK_DEAD, or it can be valid with TASK_DEAD.
For example, an autoreaping task can do release_task(current)
long before it sets TASK_DEAD in do_exit().
Or, a zombie task can have ->state == TASK_DEAD but release_task()
was not called, and in this case we must not break the loop.
Change this code to check pid_alive() instead, and do this before we drop
the reference to the task_struct.
Note: while_each_thread() under rcu_read_lock() is not really safe, it can
livelock. This will be fixed later, but fortunately in this case the
"max_count" logic saves us anyway.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Mandeep Singh Baines <msb@google.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Previously it was (ab)used by utrace. Then it was wrongly used by the
scheduler code.
Currently it is not used, kill it before it finds the new erroneous user.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Now that CLONE_VFORK is killable, coredump_wait() no longer needs
complete_vfork_done(). zap_threads() should find and kill all tasks with
the same ->mm, this includes our parent if ->vfork_done is set.
mm_release() becomes the only caller, unexport complete_vfork_done().
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Make vfork() killable.
Change do_fork(CLONE_VFORK) to do wait_for_completion_killable(). If it
fails we do not return to the user-mode and never touch the memory shared
with our child.
However, in this case we should clear child->vfork_done before return, we
use task_lock() in do_fork()->wait_for_vfork_done() and
complete_vfork_done() to serialize with each other.
Note: now that we use task_lock() we don't really need completion, we
could turn task->vfork_done into "task_struct *wake_up_me" but this needs
some complications.
NOTE: this and the next patches do not affect in-kernel users of
CLONE_VFORK, kernel threads run with all signals ignored including
SIGKILL/SIGSTOP.
However this is obviously the user-visible change. Not only a fatal
signal can kill the vforking parent, a sub-thread can do execve or
exit_group() and kill the thread sleeping in vfork().
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
No functional changes.
Move the clear-and-complete-vfork_done code into the new trivial helper,
complete_vfork_done().
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
register_kprobe() aborts if the address of the new request falls in a
prohibited area (such as ftrace pouch, __kprobes annotated functions,
non-kernel text addresses, jump label text). We however don't return the
right error on this abort, resulting in a silent failure - incorrect
adding/reporting of kprobes ('perf probe do_fork+18' or 'perf probe
mcount' for instance).
In V2 we are incorporating Masami Hiramatsu's feedback.
This patch fixes it by returning -EINVAL upon failure.
While we are here, rename the label used for exit to be more appropriate.
Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: Prashanth K Nageshappa <prashanth@linux.vnet.ibm.com>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Jason Baron <jbaron@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Since commit 04c6862c05 ("kmsg_dump: add kmsg_dump() calls to the
reboot, halt, poweroff and emergency_restart paths"), kmsg_dump() gets
run on normal paths including poweroff and reboot.
This is less than ideal given pstore implementations that can only
represent single backtraces, since a reboot may overwrite a stored oops
before it's been picked up by userspace. In addition, some pstore
backends may have low performance and provide a significant delay in
reboot as a result.
This patch adds a printk.always_kmsg_dump kernel parameter (which can also
be changed from userspace). Without it, the code will only be run on
failure paths rather than on normal paths. The option can be enabled in
environments where there's a desire to attempt to audit whether or not a
reboot was cleanly requested or not.
Signed-off-by: Matthew Garrett <mjg@redhat.com>
Acked-by: Seiji Aguchi <seiji.aguchi@hds.com>
Cc: Seiji Aguchi <seiji.aguchi@hds.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Marco Stornelli <marco.stornelli@gmail.com>
Cc: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Don Zickus <dzickus@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Pulling latest branches from Ingo:
* 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
memblock: Fix size aligning of memblock_alloc_base_nid()
* 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
perf probe: Ensure offset provided is not greater than function length without DWARF info too
perf tools: Ensure comm string is properly terminated
perf probe: Ensure offset provided is not greater than function length
perf evlist: Return first evsel for non-sample event on old kernel
perf/hwbp: Fix a possible memory leak
* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
CPU hotplug, cpusets, suspend: Don't touch cpusets during suspend/resume
This patch (as1519) fixes a bug in the block layer's disk-events
polling. The polling is done by a work routine queued on the
system_nrt_wq workqueue. Since that workqueue isn't freezable, the
polling continues even in the middle of a system sleep transition.
Obviously, polling a suspended drive for media changes and such isn't
a good thing to do; in the case of USB mass-storage devices it can
lead to real problems requiring device resets and even re-enumeration.
The patch fixes things by creating a new system-wide, non-reentrant,
freezable workqueue and using it for disk-events polling.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: <stable@kernel.org>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
The major features of this series are:
- making RCU more aggressive about entering dyntick-idle mode in order to
improve energy efficiency
- converting a few more call_rcu()s to kfree_rcu()s
- applying a number of rcutree fixes and cleanups to rcutiny
- removing CONFIG_SMP #ifdefs from treercu
- allowing RCU CPU stall times to be set via sysfs
- adding CPU-stall capability to rcutorture
- adding more RCU-abuse diagnostics
- updating documentation
- fixing yet more issues located by the still-ongoing top-to-bottom
inspection of RCU, this time with a special focus on the
CPU-hotplug code path.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
If kzalloc() for TYPE_DATA failed on a given cpu, previous chunk
of TYPE_INST will be leaked. Fix it.
Thanks to Peter Zijlstra for suggesting this better solution. It
should work as long as the initial value of the region is all
0's and that's the case of static (per-cpu) memory allocation.
Signed-off-by: Namhyung Kim <namhyung.kim@lge.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Link: http://lkml.kernel.org/r/1330391978-28070-1-git-send-email-namhyung.kim@lge.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
* 'irq-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
genirq: Handle pending irqs in irq_startup()
genirq: Unmask oneshot irqs when thread was not woken
Currently, during CPU hotplug, the cpuset callbacks modify the cpusets
to reflect the state of the system, and this handling is asymmetric.
That is, upon CPU offline, that CPU is removed from all cpusets. However
when it comes back online, it is put back only to the root cpuset.
This gives rise to a significant problem during suspend/resume. During
suspend, we offline all non-boot cpus and during resume we online them back.
Which means, after a resume, all cpusets (except the root cpuset) will be
restricted to just one single CPU (the boot cpu). But the whole point of
suspend/resume is to restore the system to a state which is as close as
possible to how it was before suspend.
So to fix this, don't touch cpusets during suspend/resume. That is, modify
the cpuset-related CPU hotplug callback to just ignore CPU hotplug when it
is initiated as part of the suspend/resume sequence.
Reported-by: Prashanth Nageshappa <prashanth@linux.vnet.ibm.com>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/4F460D7B.1020703@linux.vnet.ibm.com
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This patch is intentionally incomplete to simplify the review.
It ignores ep_unregister_pollwait() which plays with the same wqh.
See the next change.
epoll assumes that the EPOLL_CTL_ADD'ed file controls everything
f_op->poll() needs. In particular it assumes that the wait queue
can't go away until eventpoll_release(). This is not true in case
of signalfd, the task which does EPOLL_CTL_ADD uses its ->sighand
which is not connected to the file.
This patch adds the special event, POLLFREE, currently only for
epoll. It expects that init_poll_funcptr()'ed hook should do the
necessary cleanup. Perhaps it should be defined as EPOLLFREE in
eventpoll.
__cleanup_sighand() is changed to do wake_up_poll(POLLFREE) if
->signalfd_wqh is not empty, we add the new signalfd_cleanup()
helper.
ep_poll_callback(POLLFREE) simply does list_del_init(task_list).
This make this poll entry inconsistent, but we don't care. If you
share epoll fd which contains our sigfd with another process you
should blame yourself. signalfd is "really special". I simply do
not know how we can define the "right" semantics if it used with
epoll.
The main problem is, epoll calls signalfd_poll() once to establish
the connection with the wait queue, after that signalfd_poll(NULL)
returns the different/inconsistent results depending on who does
EPOLL_CTL_MOD/signalfd_read/etc. IOW: apart from sigmask, signalfd
has nothing to do with the file, it works with the current thread.
In short: this patch is the hack which tries to fix the symptoms.
It also assumes that nobody can take tasklist_lock under epoll
locks, this seems to be true.
Note:
- we do not have wake_up_all_poll() but wake_up_poll()
is fine, poll/epoll doesn't use WQ_FLAG_EXCLUSIVE.
- signalfd_cleanup() uses POLLHUP along with POLLFREE,
we need a couple of simple changes in eventpoll.c to
make sure it can't be "lost".
Reported-by: Maxime Bizon <mbizon@freebox.fr>
Cc: <stable@kernel.org>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Commit 1ac9bc69 ("sched/tracing: Add a new tracepoint for sleeptime")
added a new sched:sched_stat_sleeptime tracepoint.
It's broken: the first sample we get on a task might be bad because
of a stale sleep_start value that wasn't reset at the last task switch
because the tracepoint was not active.
It also breaks the existing schedstat samples due to the side
effects of:
- se->statistics.sleep_start = 0;
...
- se->statistics.block_start = 0;
Nor do I see means to fix it without adding overhead to the scheduler
fast path, which I'm not willing to for the sake of redundant
instrumentation.
Most importantly, sleep time information can already be constructed
by tracing context switches and wakeups, and taking the timestamp
difference between the schedule-out, the wakeup and the schedule-in.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrew Vagin <avagin@openvz.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/n/tip-pc4c9qhl8q6vg3bs4j6k0rbd@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>
synchronize_sched_expedited() is spamming CONFIG_DEBUG_PREEMPT=y
users with an unintended warning from the cpu_is_offline() check: use
raw_smp_processor_id() instead of smp_processor_id() there.
Because the warning is under a get_online_cpus(), it is not possible
for any CPUs to go offline, though it is quite possible that the
task might migrate between the raw_smp_processor_id() and the check
of cpu_is_offline(). This is not a problem because the task cannot
migrate from an offline CPU to an online one or vice versa. The point
of the check is to verify that synchronize_sched_expedited() is not
called from an offline CPU, for example, from a CPU_DYING notifier, or,
more important, from an outgoing CPU making its way from its CPU_DYING
notifiers to the idle loop.
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit handles workloads that transition quickly between idle and
non-idle, and where the CPU's callbacks cannot be invoked, but where
RCU does not have anything immediate for the CPU to do. Without this
patch, the RCU_FAST_NO_HZ code can be invoked repeatedly on each entry
to idle. The commit sets the per-CPU rcu_dyntick_holdoff variable to
hold off further attempts for a tick.
Reported-by: "Abou Gazala, Neven M" <neven.m.abou.gazala@intel.com>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
If a softirq is pending, the current CPU has RCU callbacks pending,
and RCU does not immediately need anything from this CPU, then the
current code resets the RCU_FAST_NO_HZ state machine. This means that
upon exit from the subsequent softirq handler, RCU_FAST_NO_HZ will
try really hard to force RCU into dyntick-idle mode. And if the same
conditions hold after a few tries (determined by RCU_IDLE_OPT_FLUSHES),
the same situation can repeat, possibly endlessly. This scenario is
not particularly good for battery lifetime.
This commit therefore suppresses the early exit from the RCU_FAST_NO_HZ
state machine in the case where there is a softirq pending. This change
forces the state machine to retain its memory, and to enter holdoff if
this condition persists.
Reported-by: "Abou Gazala, Neven M" <neven.m.abou.gazala@intel.com>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden
in the inner idle loop, that is, between the rcu_idle_enter() and the
rcu_idle_exit() -- RCU will happily ignore any such read-side critical
sections. However, things like powertop need tracepoints in the inner
idle loop.
This commit therefore provides an RCU_NONIDLE() macro that can be used to
wrap code in the idle loop that requires RCU read-side critical sections.
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Acked-by: Deepthi Dharwar <deepthi@linux.vnet.ibm.com>
Use of RCU in the idle loop is incorrect, quite a few instances of
just that have made their way into mainline, primarily event tracing.
The problem with RCU read-side critical sections on CPUs that RCU believes
to be idle is that RCU is completely ignoring the CPU, along with any
attempts and RCU read-side critical sections.
The approaches of eliminating the offending uses and of pushing the
definition of idle down beyond the offending uses have both proved
impractical. The new approach is to encapsulate offending uses of RCU
with rcu_idle_exit() and rcu_idle_enter(), but this requires nesting
for code that is invoked both during idle and and during normal execution.
Therefore, this commit modifies rcu_idle_enter() and rcu_idle_exit() to
permit nesting.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Acked-by: Deepthi Dharwar <deepthi@linux.vnet.ibm.com>
There is now an unconditional check for rcu_head misalignment in
__call_rcu(), so remove the old conditional one in debug_rcu_head_queue().
Reported-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The semantic match that finds this problem is as follows:
(http://coccinelle.lip6.fr/)
// <smpl>
@@
expression e,e1;
constant c;
@@
*e = c
... when != e = e1
when != &e
when != true IS_ERR(e)
*PTR_ERR(e)
// </smpl>
Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Reported-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Fix a bonehead error introduced when adding event tracing to rcutorture.
Move the traces to follow the NULL-pointer checks.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The expedited RCU primitives can be quite useful, but they have some
high costs as well. This commit updates and creates docbook comments
calling out the costs, and updates the RCU documentation as well.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Because newly offlined CPUs continue executing after completing the
CPU_DYING notifiers, they legitimately enter the scheduler and use
RCU while appearing to be offline. This calls for a more sophisticated
approach as follows:
1. RCU marks the CPU online during the CPU_UP_PREPARE phase.
2. RCU marks the CPU offline during the CPU_DEAD phase.
3. Diagnostics regarding use of read-side RCU by offline CPUs use
RCU's accounting rather than the cpu_online_map. (Note that
__call_rcu() still uses cpu_online_map to detect illegal
invocations within CPU_DYING notifiers.)
4. Offline CPUs are prevented from hanging the system by
force_quiescent_state(), which pays attention to cpu_online_map.
Some additional work (in a later commit) will be needed to
guarantee that force_quiescent_state() waits a full jiffy before
assuming that a CPU is offline, for example, when called from
idle entry. (This commit also makes the one-jiffy wait
explicit, since the old-style implicit wait can now be defeated
by RCU_FAST_NO_HZ and by rcutorture.)
This approach avoids the false positives encountered when attempting to
use more exact classification of CPU online/offline state.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
It is illegal to use RCU from a CPU that has reported idleness or
offlinedness to RCU. However, it can be quite difficult to determine
from a stack trace whether or not a given CPU is idle or offline.
Therefore, this commit adds idle/offline diagnostics to the lockdep-RCU
error message.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The rcu_prepare_for_idle() function is always called with interrupts
disabled, so there is no reason to disable interrupts again within
rcu_prepare_for_idle(). Therefore, this commit removes all of the
interrupt disabling, also removing a latent disabling-unbalance bug.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Now that TREE_RCU and TREE_PREEMPT_RCU no longer do anything different
for the single-CPU case, there is no need for multiple definitions of
synchronize_sched_expedited(). It is no longer in any sense a plug-in,
so move it from kernel/rcutree_plugin.h to kernel/rcutree.c.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Although it is legal to use RCU during early boot, it is anything
but legal to use RCU at runtime from an offlined CPU. After all, RCU
explicitly ignores offlined CPUs. This commit therefore adds checks
for runtime use of RCU from offlined CPUs.
These checks are not perfect, in particular, they can be subverted
through use of things like rcu_dereference_raw(). Note that it is not
possible to put checks in rcu_read_lock() and friends due to the fact
that these primitives are used in code that might be used under either
RCU or lock-based protection, which means that checking rcu_read_lock()
gets you fat piles of false positives.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Add module parameters to rcutorture that induce a CPU stall.
The stall_cpu parameter specifies how long to stall in seconds,
defaulting to zero, which indicates no stalling is to be undertaken.
The stall_cpu_holdoff parameter specifies how many seconds after
insmod (or boot, if rcutorture is built into the kernel) that this
stall is to start. The default value for stall_cpu_holdoff is ten
seconds.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
When rcutorture is started automatically at boot time, it might well
also start CPU-hotplug operations at that time, which might not be
desirable. This commit therefore adds an rcutorture parameter that
allows CPU-hotplug operations to be held off for the specified number
of seconds after the start of boot.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
There have been situations where RCU CPU stall warnings were caused by
issues in scheduling-clock timer initialization. To make it easier to
track these down, this commit causes the RCU CPU stall-warning messages
to print out the number of scheduling-clock interrupts taken in the
current grace period for each stalled CPU.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The default CONFIG_RCU_CPU_STALL_TIMEOUT value of 60 seconds has served
Linux users well for production use for quite some time. However, for
debugging, there will be more than three minutes between subsequent
stall-warning messages. This can be an annoyingly long wait if you
are trying to work out where the offending infinite loop is hiding.
Therefore, this commit provides a rcu_cpu_stall_timeout sysfs
parameter that may be adjusted at boot time and at runtime to speed
up debugging.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Now that both TINY_RCU and TINY_PREEMPT_RCU have been in place for awhile,
it is time to remove UP support from TREE_RCU, which is what this commit
does.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The inner idle loop is an extended quiescent state for all flavors
of RCU, but there have been recent bug involving use of RCU read-side
primitives from within the idle loop. Therefore, this commit enlists
lockdep-RCU to detect attempts to enter the inner idle loop while in
an RCU read-side critical section, emitting a lockdep-RCU splat if so.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The recent updates to RCU_CPU_FAST_NO_HZ have an rcu_needs_cpu() that
does more than just check for callbacks, so get the name for
rcu_preempt_needs_cpu() consistent with that change, now calling it
rcu_preempt_cpu_has_callbacks().
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This is a port of commit #82e78d80 from TREE_PREEMPT_RCU to
TINY_PREEMPT_RCU.
This commit uses the fact that current->rcu_boost_mutex is set
any time that the RCU_READ_UNLOCK_BOOSTED flag is set in the
current->rcu_read_unlock_special bitmask. This allows tests of
the bit to be changed to tests of the pointer, which in turn allows
the RCU_READ_UNLOCK_BOOSTED flag to be eliminated.
Please note that the check of current->rcu_read_unlock_special need not
change because any time that RCU_READ_UNLOCK_BOOSTED was set, so was
RCU_READ_UNLOCK_BLOCKED. Therefore, __rcu_read_unlock() can continue
testing current->rcu_read_unlock_special for non-zero, as before.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This is a port to TINY_RCU of Peter Zijlstra's commit #ec433f0c5
The rcu_read_unlock_special() function relies on in_irq() to exclude
scheduler activity from interrupt level. This fails because exit_irq()
can invoke the scheduler after clearing the preempt_count() bits that
in_irq() uses to determine that it is at interrupt level. This situation
can result in failures as follows:
$task IRQ SoftIRQ
rcu_read_lock()
/* do stuff */
<preempt> |= UNLOCK_BLOCKED
rcu_read_unlock()
--t->rcu_read_lock_nesting
irq_enter();
/* do stuff, don't use RCU */
irq_exit();
sub_preempt_count(IRQ_EXIT_OFFSET);
invoke_softirq()
ttwu();
spin_lock_irq(&pi->lock)
rcu_read_lock();
/* do stuff */
rcu_read_unlock();
rcu_read_unlock_special()
rcu_report_exp_rnp()
ttwu()
spin_lock_irq(&pi->lock) /* deadlock */
rcu_read_unlock_special(t);
This can be triggered 'easily' because invoke_softirq() immediately does
a ttwu() of ksoftirqd/# instead of doing the in-place softirq stuff first,
but even without that the above happens.
Cure this by also excluding softirqs from the rcu_read_unlock_special()
handler and ensuring the force_irqthreads ksoftirqd/# wakeup is done
from full softirq context.
It is also necessary to delay the ->rcu_read_lock_nesting decrement until
after rcu_read_unlock_special(). This delay is handled by the commit
"Protect __rcu_read_unlock() against scheduler-using irq handlers".
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This is a port of commit #b0d3041 from TREE_RCU to TREE_PREEMPT_RCU.
Under some rare but real combinations of configuration parameters, RCU
callbacks are posted during early boot that use kernel facilities that are
not yet initialized. Therefore, when these callbacks are invoked, hard
hangs and crashes ensue. This commit therefore prevents RCU callbacks
from being invoked until after the scheduler is fully up and running,
as in after multiple tasks have been spawned.
It might well turn out that a better approach is to identify the specific
RCU callbacks that are causing this problem, but that discussion will
wait until such time as someone really needs an RCU callback to be invoked
(as opposed to merely registered) during early boot.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This is a port of commit #be0e1e21 to TINY_PREEMPT_RCU. This uses
noinline to prevent rcu_read_unlock_special() from being inlined into
__rcu_read_unlock().
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit ports commit #10f39bb1b2 (rcu: protect __rcu_read_unlock()
against scheduler-using irq handlers) from TREE_PREEMPT_RCU to
TINY_PREEMPT_RCU. The following is a corresponding port of that
commit message.
The addition of RCU read-side critical sections within runqueue and
priority-inheritance critical sections introduced some deadlocks,
for example, involving interrupts from __rcu_read_unlock() where the
interrupt handlers call wake_up(). This situation can cause the
instance of __rcu_read_unlock() invoked from interrupt to do some
of the processing that would otherwise have been carried out by the
task-level instance of __rcu_read_unlock(). When the interrupt-level
instance of __rcu_read_unlock() is called with a scheduler lock held from
interrupt-entry/exit situations where in_irq() returns false, deadlock can
result. Of course, in a UP kernel, there are not really any deadlocks,
but the upper-level critical section can still be be fatally confused
by the lower-level critical section changing things out from under it.
This commit resolves these deadlocks by using negative values of the
per-task ->rcu_read_lock_nesting counter to indicate that an instance of
__rcu_read_unlock() is in flight, which in turn prevents instances from
interrupt handlers from doing any special processing. Note that nested
rcu_read_lock()/rcu_read_unlock() pairs are still permitted, but they will
never see ->rcu_read_lock_nesting go to zero, and will therefore never
invoke rcu_read_unlock_special(), thus preventing them from seeing the
RCU_READ_UNLOCK_BLOCKED bit should it be set in ->rcu_read_unlock_special.
This patch also adds a check for ->rcu_read_unlock_special being negative
in rcu_check_callbacks(), thus preventing the RCU_READ_UNLOCK_NEED_QS
bit from being set should a scheduling-clock interrupt occur while
__rcu_read_unlock() is exiting from an outermost RCU read-side critical
section.
Of course, __rcu_read_unlock() can be preempted during the time that
->rcu_read_lock_nesting is negative. This could result in the setting
of the RCU_READ_UNLOCK_BLOCKED bit after __rcu_read_unlock() checks it,
and would also result it this task being queued on the corresponding
rcu_node structure's blkd_tasks list. Therefore, some later RCU read-side
critical section would enter rcu_read_unlock_special() to clean up --
which could result in deadlock (OK, OK, fatal confusion) if that RCU
read-side critical section happened to be in the scheduler where the
runqueue or priority-inheritance locks were held.
To prevent the possibility of fatal confusion that might result from
preemption during the time that ->rcu_read_lock_nesting is negative,
this commit also makes rcu_preempt_note_context_switch() check for
negative ->rcu_read_lock_nesting, thus refraining from queuing the task
(and from setting RCU_READ_UNLOCK_BLOCKED) if we are already exiting
from the outermost RCU read-side critical section (in other words,
we really are no longer actually in that RCU read-side critical
section). In addition, rcu_preempt_note_context_switch() invokes
rcu_read_unlock_special() to carry out the cleanup in this case, which
clears out the ->rcu_read_unlock_special bits and dequeues the task
(if necessary), in turn avoiding needless delay of the current RCU grace
period and needless RCU priority boosting.
It is still illegal to call rcu_read_unlock() while holding a scheduler
lock if the prior RCU read-side critical section has ever had both
preemption and irqs enabled. However, the common use case is legal,
namely where then entire RCU read-side critical section executes with
irqs disabled, for example, when the scheduler lock is held across the
entire lifetime of the RCU read-side critical section.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The grace-period initialization sequence in rcu_start_gp() has a special
case for systems where the rcu_node tree is a single rcu_node structure.
This made sense some years ago when systems were smaller and up to 64
CPUs could share a single rcu_node structure, but now that large systems
are common and a given leaf rcu_node structure can support only 16 CPUs
(due to lock contention on the rcu_node's ->lock field), this optimization
is almost never taken. And even the small mobile platforms that might
make use of it might rather have the kernel text reduction.
Therefore, this commit removes the check for single-rcu_node trees.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
RCU's current CPU-offline code path dumps all of the outgoing CPU's
callbacks onto the RCU_NEXT_TAIL portion of the surviving CPU's
callback list. This means that all the ready-to-invoke callbacks from
the outgoing CPU must wait for another full RCU grace period. This was
just fine when CPU-hotplug events were rare, but there is increasing
evidence that users are planning to make increasing use of CPU hotplug.
Therefore, this commit changes the callback-dumping procedure so that
callbacks that are ready to invoke are moved to the RCU_DONE_TAIL
portion of the surviving CPU's callback list. This avoids running
these callbacks through a second unnecessary grace period.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Linus Torvalds
Cyrill Gorcunov
Thomas Gleixner
Oleg Nesterov
Prashanth Nageshappa
Matthew Garrett
Alan Stern
Ingo Molnar
Namhyung Kim
Srivatsa S. Bhat
Peter Zijlstra
Hugh Dickins
Paul E. McKenney
Paul E. McKenney
Julia Lawall