Commit Graph

418 Commits

Author SHA1 Message Date
Tejun Heo 3d1cb2059d workqueue: include workqueue info when printing debug dump of a worker task
One of the problems that arise when converting dedicated custom
threadpool to workqueue is that the shared worker pool used by workqueue
anonimizes each worker making it more difficult to identify what the
worker was doing on which target from the output of sysrq-t or debug
dump from oops, BUG() and friends.

This patch implements set_worker_desc() which can be called from any
workqueue work function to set its description.  When the worker task is
dumped for whatever reason - sysrq-t, WARN, BUG, oops, lockdep assertion
and so on - the description will be printed out together with the
workqueue name and the worker function pointer.

The printing side is implemented by print_worker_info() which is called
from functions in task dump paths - sched_show_task() and
dump_stack_print_info().  print_worker_info() can be safely called on
any task in any state as long as the task struct itself is accessible.
It uses probe_*() functions to access worker fields.  It may print
garbage if something went very wrong, but it wouldn't cause (another)
oops.

The description is currently limited to 24bytes including the
terminating \0.  worker->desc_valid and workder->desc[] are added and
the 64 bytes marker which was already incorrect before adding the new
fields is moved to the correct position.

Here's an example dump with writeback updated to set the bdi name as
worker desc.

 Hardware name: Bochs
 Modules linked in:
 Pid: 7, comm: kworker/u9:0 Not tainted 3.9.0-rc1-work+ #1
 Workqueue: writeback bdi_writeback_workfn (flush-8:0)
  ffffffff820a3ab0 ffff88000f6e9cb8 ffffffff81c61845 ffff88000f6e9cf8
  ffffffff8108f50f 0000000000000000 0000000000000000 ffff88000cde16b0
  ffff88000cde1aa8 ffff88001ee19240 ffff88000f6e9fd8 ffff88000f6e9d08
 Call Trace:
  [<ffffffff81c61845>] dump_stack+0x19/0x1b
  [<ffffffff8108f50f>] warn_slowpath_common+0x7f/0xc0
  [<ffffffff8108f56a>] warn_slowpath_null+0x1a/0x20
  [<ffffffff81200150>] bdi_writeback_workfn+0x2a0/0x3b0
 ...

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Acked-by: Jan Kara <jack@suse.cz>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Dave Chinner <david@fromorbit.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-04-30 17:04:02 -07:00
Wei Yongjun cece95dfe5 workqueue: use kmem_cache_free() instead of kfree()
memory allocated by kmem_cache_alloc() should be freed using
kmem_cache_free(), not kfree().

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Tejun Heo <tj@kernel.org>
2013-04-09 11:33:40 -07:00
Lai Jiangshan 5c529597e9 workqueue: avoid false negative WARN_ON() in destroy_workqueue()
destroy_workqueue() performs several sanity checks before proceeding
with destruction of a workqueue.  One of the checks verifies that
refcnt of each pwq (pool_workqueue) is over 1 as at that point there
should be no in-flight work items and the only holder of pwq refs is
the workqueue itself.

This worked fine as a workqueue used to hold only one reference to its
pwqs; however, since 4c16bd327c ("workqueue: implement NUMA affinity
for unbound workqueues"), a workqueue may hold multiple references to
its default pwq triggering this sanity check spuriously.

Fix it by not triggering the pwq->refcnt assertion on default pwqs.

An example spurious WARN trigger follows.

 WARNING: at kernel/workqueue.c:4201 destroy_workqueue+0x6a/0x13e()
 Hardware name: 4286C12
 Modules linked in: sdhci_pci sdhci mmc_core usb_storage i915 drm_kms_helper drm i2c_algo_bit i2c_core video
 Pid: 361, comm: umount Not tainted 3.9.0-rc5+ #29
 Call Trace:
  [<c04314a7>] warn_slowpath_common+0x7c/0x93
  [<c04314e0>] warn_slowpath_null+0x22/0x24
  [<c044796a>] destroy_workqueue+0x6a/0x13e
  [<c056dc01>] ext4_put_super+0x43/0x2c4
  [<c04fb7b8>] generic_shutdown_super+0x4b/0xb9
  [<c04fb848>] kill_block_super+0x22/0x60
  [<c04fb960>] deactivate_locked_super+0x2f/0x56
  [<c04fc41b>] deactivate_super+0x2e/0x31
  [<c050f1e6>] mntput_no_expire+0x103/0x108
  [<c050fdce>] sys_umount+0x2a2/0x2c4
  [<c050fe0e>] sys_oldumount+0x1e/0x20
  [<c085ba4d>] sysenter_do_call+0x12/0x38

tj: Rewrote description.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
2013-04-04 07:54:01 -07:00
Tejun Heo 229641a6f1 Linux 3.9-rc5
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 k1JnbRbiPsLsCVFOn10SQkGDAIk00lro3tuWP2C1ljERiD/OOh5Ui9nXYAhMkbI=
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Merge tag 'v3.9-rc5' into wq/for-3.10

Writeback conversion to workqueue will be based on top of wq/for-3.10
branch to take advantage of custom attrs and NUMA support for unbound
workqueues.  Mainline currently contains two commits which result in
non-trivial merge conflicts with wq/for-3.10 and because
block/for-3.10/core is based on v3.9-rc3 which contains one of the
conflicting commits, we need a pre-merge-window merge anyway.  Let's
pull v3.9-rc5 into wq/for-3.10 so that the block tree doesn't suffer
from workqueue merge conflicts.

The two conflicts and their resolutions:

* e68035fb65 ("workqueue: convert to idr_alloc()") in mainline changes
  worker_pool_assign_id() to use idr_alloc() instead of the old idr
  interface.  worker_pool_assign_id() goes through multiple locking
  changes in wq/for-3.10 causing the following conflict.

  static int worker_pool_assign_id(struct worker_pool *pool)
  {
	  int ret;

  <<<<<<< HEAD
	  lockdep_assert_held(&wq_pool_mutex);

	  do {
		  if (!idr_pre_get(&worker_pool_idr, GFP_KERNEL))
			  return -ENOMEM;
		  ret = idr_get_new(&worker_pool_idr, pool, &pool->id);
	  } while (ret == -EAGAIN);
  =======
	  mutex_lock(&worker_pool_idr_mutex);
	  ret = idr_alloc(&worker_pool_idr, pool, 0, 0, GFP_KERNEL);
	  if (ret >= 0)
		  pool->id = ret;
	  mutex_unlock(&worker_pool_idr_mutex);
  >>>>>>> c67bf5361e7e66a0ff1f4caf95f89347d55dfb89

	  return ret < 0 ? ret : 0;
  }

  We want locking from the former and idr_alloc() usage from the
  latter, which can be combined to the following.

  static int worker_pool_assign_id(struct worker_pool *pool)
  {
	  int ret;

	  lockdep_assert_held(&wq_pool_mutex);

	  ret = idr_alloc(&worker_pool_idr, pool, 0, 0, GFP_KERNEL);
	  if (ret >= 0) {
		  pool->id = ret;
		  return 0;
	  }
	  return ret;
   }

* eb2834285c ("workqueue: fix possible pool stall bug in
  wq_unbind_fn()") updated wq_unbind_fn() such that it has single
  larger for_each_std_worker_pool() loop instead of two separate loops
  with a schedule() call inbetween.  wq/for-3.10 renamed
  pool->assoc_mutex to pool->manager_mutex causing the following
  conflict (earlier function body and comments omitted for brevity).

  static void wq_unbind_fn(struct work_struct *work)
  {
  ...
		  spin_unlock_irq(&pool->lock);
  <<<<<<< HEAD
		  mutex_unlock(&pool->manager_mutex);
	  }
  =======
		  mutex_unlock(&pool->assoc_mutex);
  >>>>>>> c67bf5361e7e66a0ff1f4caf95f89347d55dfb89

		  schedule();

  <<<<<<< HEAD
	  for_each_cpu_worker_pool(pool, cpu)
  =======
  >>>>>>> c67bf5361e7e66a0ff1f4caf95f89347d55dfb89
		  atomic_set(&pool->nr_running, 0);

		  spin_lock_irq(&pool->lock);
		  wake_up_worker(pool);
		  spin_unlock_irq(&pool->lock);
	  }
  }

  The resolution is mostly trivial.  We want the control flow of the
  latter with the rename of the former.

  static void wq_unbind_fn(struct work_struct *work)
  {
  ...
		  spin_unlock_irq(&pool->lock);
		  mutex_unlock(&pool->manager_mutex);

		  schedule();

		  atomic_set(&pool->nr_running, 0);

		  spin_lock_irq(&pool->lock);
		  wake_up_worker(pool);
		  spin_unlock_irq(&pool->lock);
	  }
  }

Signed-off-by: Tejun Heo <tj@kernel.org>
2013-04-01 18:45:36 -07:00
Tejun Heo d55262c4d1 workqueue: update sysfs interface to reflect NUMA awareness and a kernel param to disable NUMA affinity
Unbound workqueues are now NUMA aware.  Let's add some control knobs
and update sysfs interface accordingly.

* Add kernel param workqueue.numa_disable which disables NUMA affinity
  globally.

* Replace sysfs file "pool_id" with "pool_ids" which contain
  node:pool_id pairs.  This change is userland-visible but "pool_id"
  hasn't seen a release yet, so this is okay.

* Add a new sysf files "numa" which can toggle NUMA affinity on
  individual workqueues.  This is implemented as attrs->no_numa whichn
  is special in that it isn't part of a pool's attributes.  It only
  affects how apply_workqueue_attrs() picks which pools to use.

After "pool_ids" change, first_pwq() doesn't have any user left.
Removed.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 11:23:38 -07:00
Tejun Heo 4c16bd327c workqueue: implement NUMA affinity for unbound workqueues
Currently, an unbound workqueue has single current, or first, pwq
(pool_workqueue) to which all new work items are queued.  This often
isn't optimal on NUMA machines as workers may jump around across node
boundaries and work items get assigned to workers without any regard
to NUMA affinity.

This patch implements NUMA affinity for unbound workqueues.  Instead
of mapping all entries of numa_pwq_tbl[] to the same pwq,
apply_workqueue_attrs() now creates a separate pwq covering the
intersecting CPUs for each NUMA node which has online CPUs in
@attrs->cpumask.  Nodes which don't have intersecting possible CPUs
are mapped to pwqs covering whole @attrs->cpumask.

As CPUs come up and go down, the pool association is changed
accordingly.  Changing pool association may involve allocating new
pools which may fail.  To avoid failing CPU_DOWN, each workqueue
always keeps a default pwq which covers whole attrs->cpumask which is
used as fallback if pool creation fails during a CPU hotplug
operation.

This ensures that all work items issued on a NUMA node is executed on
the same node as long as the workqueue allows execution on the CPUs of
the node.

As this maps a workqueue to multiple pwqs and max_active is per-pwq,
this change the behavior of max_active.  The limit is now per NUMA
node instead of global.  While this is an actual change, max_active is
already per-cpu for per-cpu workqueues and primarily used as safety
mechanism rather than for active concurrency control.  Concurrency is
usually limited from workqueue users by the number of concurrently
active work items and this change shouldn't matter much.

v2: Fixed pwq freeing in apply_workqueue_attrs() error path.  Spotted
    by Lai.

v3: The previous version incorrectly made a workqueue spanning
    multiple nodes spread work items over all online CPUs when some of
    its nodes don't have any desired cpus.  Reimplemented so that NUMA
    affinity is properly updated as CPUs go up and down.  This problem
    was spotted by Lai Jiangshan.

v4: destroy_workqueue() was putting wq->dfl_pwq and then clearing it;
    however, wq may be freed at any time after dfl_pwq is put making
    the clearing use-after-free.  Clear wq->dfl_pwq before putting it.

v5: apply_workqueue_attrs() was leaking @tmp_attrs, @new_attrs and
    @pwq_tbl after success.  Fixed.

    Retry loop in wq_update_unbound_numa_attrs() isn't necessary as
    application of new attrs is excluded via CPU hotplug.  Removed.

    Documentation on CPU affinity guarantee on CPU_DOWN added.

    All changes are suggested by Lai Jiangshan.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 11:23:36 -07:00
Tejun Heo dce90d47c4 workqueue: introduce put_pwq_unlocked()
Factor out lock pool, put_pwq(), unlock sequence into
put_pwq_unlocked().  The two existing places are converted and there
will be more with NUMA affinity support.

This is to prepare for NUMA affinity support for unbound workqueues
and doesn't introduce any functional difference.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 11:23:35 -07:00
Tejun Heo 1befcf3073 workqueue: introduce numa_pwq_tbl_install()
Factor out pool_workqueue linking and installation into numa_pwq_tbl[]
from apply_workqueue_attrs() into numa_pwq_tbl_install().  link_pwq()
is made safe to call multiple times.  numa_pwq_tbl_install() links the
pwq, installs it into numa_pwq_tbl[] at the specified node and returns
the old entry.

@last_pwq is removed from link_pwq() as the return value of the new
function can be used instead.

This is to prepare for NUMA affinity support for unbound workqueues.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 11:23:35 -07:00
Tejun Heo e50aba9aea workqueue: use NUMA-aware allocation for pool_workqueues
Use kmem_cache_alloc_node() with @pool->node instead of
kmem_cache_zalloc() when allocating a pool_workqueue so that it's
allocated on the same node as the associated worker_pool.  As there's
no no kmem_cache_zalloc_node(), move zeroing to init_pwq().

This was suggested by Lai Jiangshan.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 11:23:35 -07:00
Tejun Heo f147f29eb7 workqueue: break init_and_link_pwq() into two functions and introduce alloc_unbound_pwq()
Break init_and_link_pwq() into init_pwq() and link_pwq() and move
unbound-workqueue specific handling into apply_workqueue_attrs().
Also, factor out unbound pool and pool_workqueue allocation into
alloc_unbound_pwq().

This reorganization is to prepare for NUMA affinity and doesn't
introduce any functional changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 11:23:35 -07:00
Tejun Heo df2d5ae499 workqueue: map an unbound workqueues to multiple per-node pool_workqueues
Currently, an unbound workqueue has only one "current" pool_workqueue
associated with it.  It may have multple pool_workqueues but only the
first pool_workqueue servies new work items.  For NUMA affinity, we
want to change this so that there are multiple current pool_workqueues
serving different NUMA nodes.

Introduce workqueue->numa_pwq_tbl[] which is indexed by NUMA node and
points to the pool_workqueue to use for each possible node.  This
replaces first_pwq() in __queue_work() and workqueue_congested().

numa_pwq_tbl[] is currently initialized to point to the same
pool_workqueue as first_pwq() so this patch doesn't make any behavior
changes.

v2: Use rcu_dereference_raw() in unbound_pwq_by_node() as the function
    may be called only with wq->mutex held.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 11:23:35 -07:00
Tejun Heo 2728fd2f09 workqueue: move hot fields of workqueue_struct to the end
Move wq->flags and ->cpu_pwqs to the end of workqueue_struct and align
them to the cacheline.  These two fields are used in the work item
issue path and thus hot.  The scheduled NUMA affinity support will add
dispatch table at the end of workqueue_struct and relocating these two
fields will allow us hitting only single cacheline on hot paths.

Note that wq->pwqs isn't moved although it currently is being used in
the work item issue path for unbound workqueues.  The dispatch table
mentioned above will replace its use in the issue path, so it will
become cold once NUMA support is implemented.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 11:23:35 -07:00
Tejun Heo ecf6881ff3 workqueue: make workqueue->name[] fixed len
Currently workqueue->name[] is of flexible length.  We want to use the
flexible field for something more useful and there isn't much benefit
in allowing arbitrary name length anyway.  Make it fixed len capping
at 24 bytes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 11:23:34 -07:00
Tejun Heo 6029a91829 workqueue: add workqueue->unbound_attrs
Currently, when exposing attrs of an unbound workqueue via sysfs, the
workqueue_attrs of first_pwq() is used as that should equal the
current state of the workqueue.

The planned NUMA affinity support will make unbound workqueues make
use of multiple pool_workqueues for different NUMA nodes and the above
assumption will no longer hold.  Introduce workqueue->unbound_attrs
which records the current attrs in effect and use it for sysfs instead
of first_pwq()->attrs.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 11:23:34 -07:00
Tejun Heo f3f90ad469 workqueue: determine NUMA node of workers accourding to the allowed cpumask
When worker tasks are created using kthread_create_on_node(),
currently only per-cpu ones have the matching NUMA node specified.
All unbound workers are always created with NUMA_NO_NODE.

Now that an unbound worker pool may have an arbitrary cpumask
associated with it, this isn't optimal.  Add pool->node which is
determined by the pool's cpumask.  If the pool's cpumask is contained
inside a NUMA node proper, the pool is associated with that node, and
all workers of the pool are created on that node.

This currently only makes difference for unbound worker pools with
cpumask contained inside single NUMA node, but this will serve as
foundation for making all unbound pools NUMA-affine.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 11:23:34 -07:00
Tejun Heo e3c916a4c7 workqueue: drop 'H' from kworker names of unbound worker pools
Currently, all workqueue workers which have negative nice value has
'H' postfixed to their names.  This is necessary for per-cpu workers
as they use the CPU number instead of pool->id to identify the pool
and the 'H' postfix is the only thing distinguishing normal and
highpri workers.

As workers for unbound pools use pool->id, the 'H' postfix is purely
informational.  TASK_COMM_LEN is 16 and after the static part and
delimiters, there are only five characters left for the pool and
worker IDs.  We're expecting to have more unbound pools with the
scheduled NUMA awareness support.  Let's drop the non-essential 'H'
postfix from unbound kworker name.

While at it, restructure kthread_create*() invocation to help future
NUMA related changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 11:23:32 -07:00
Tejun Heo bce903809a workqueue: add wq_numa_tbl_len and wq_numa_possible_cpumask[]
Unbound workqueues are going to be NUMA-affine.  Add wq_numa_tbl_len
and wq_numa_possible_cpumask[] in preparation.  The former is the
highest NUMA node ID + 1 and the latter is masks of possibles CPUs for
each NUMA node.

This patch only introduces these.  Future patches will make use of
them.

v2: NUMA initialization move into wq_numa_init().  Also, the possible
    cpumask array is not created if there aren't multiple nodes on the
    system.  wq_numa_enabled bool added.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 11:23:32 -07:00
Tejun Heo a892cacc7f workqueue: move pwq_pool_locking outside of get/put_unbound_pool()
The scheduled NUMA affinity support for unbound workqueues would need
to walk workqueues list and pool related operations on each workqueue.

Move wq_pool_mutex locking out of get/put_unbound_pool() to their
callers so that pool operations can be performed while walking the
workqueues list, which is also protected by wq_pool_mutex.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 11:23:32 -07:00
Tejun Heo 4862125b02 workqueue: fix memory leak in apply_workqueue_attrs()
apply_workqueue_attrs() wasn't freeing temp attrs variable @new_attrs
in its success path.  Fix it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-04-01 11:23:31 -07:00
Tejun Heo 13e2e55601 workqueue: fix unbound workqueue attrs hashing / comparison
29c91e9912 ("workqueue: implement attribute-based unbound worker_pool
management") implemented attrs based worker_pool matching.  It tried
to avoid false negative when comparing cpumasks with custom hash
function; unfortunately, the hash and comparison functions fail to
ignore CPUs which are not possible.  It incorrectly assumed that
bitmap_copy() skips leftover bits in the last word of bitmap and
cpumask_equal() ignores impossible CPUs.

This patch updates attrs->cpumask handling such that impossible CPUs
are properly ignored.

* Hash and copy functions no longer do anything special.  They expect
  their callers to clear impossible CPUs.

* alloc_workqueue_attrs() initializes the cpumask to cpu_possible_mask
  instead of setting all bits and explicit cpumask_setall() for
  unbound_std_wq_attrs[] in init_workqueues() is dropped.

* apply_workqueue_attrs() is now responsible for ignoring impossible
  CPUs.  It makes a copy of @attrs and clears impossible CPUs before
  doing anything else.

Signed-off-by: Tejun Heo <tj@kernel.org>
2013-04-01 11:23:31 -07:00
Tejun Heo bc0caf099d workqueue: fix race condition in unbound workqueue free path
8864b4e59 ("workqueue: implement get/put_pwq()") implemented pwq
(pool_workqueue) refcnting which frees workqueue when the last pwq
goes away.  It determined whether it was the last pwq by testing
wq->pwqs is empty.  Unfortunately, the test was done outside wq->mutex
and multiple pwq release could race and try to free wq multiple times
leading to oops.

Test wq->pwqs emptiness while holding wq->mutex.

Signed-off-by: Tejun Heo <tj@kernel.org>
2013-04-01 11:23:31 -07:00
Lai Jiangshan b592760547 workqueue: remove pwq_lock which is no longer used
To simplify locking, the previous patches expanded wq->mutex to
protect all fields of each workqueue instance including the pwqs list
leaving pwq_lock without any user.  Remove the unused pwq_lock.

tj: Rebased on top of the current dev branch.  Updated description.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
2013-03-25 16:57:19 -07:00
Lai Jiangshan a357fc0326 workqueue: protect wq->saved_max_active with wq->mutex
We're expanding wq->mutex to cover all fields specific to each
workqueue with the end goal of replacing pwq_lock which will make
locking simpler and easier to understand.

This patch makes wq->saved_max_active protected by wq->mutex instead
of pwq_lock.  As pwq_lock locking around pwq_adjust_mac_active() is no
longer necessary, this patch also replaces pwq_lock lockings of
for_each_pwq() around pwq_adjust_max_active() to wq->mutex.

tj: Rebased on top of the current dev branch.  Updated description.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
2013-03-25 16:57:19 -07:00
Lai Jiangshan b09f4fd39c workqueue: protect wq->pwqs and iteration with wq->mutex
We're expanding wq->mutex to cover all fields specific to each
workqueue with the end goal of replacing pwq_lock which will make
locking simpler and easier to understand.

init_and_link_pwq() and pwq_unbound_release_workfn() already grab
wq->mutex when adding or removing a pwq from wq->pwqs list.  This
patch makes it official that the list is wq->mutex protected for
writes and updates readers accoridingly.  Explicit IRQ toggles for
sched-RCU read-locking in flush_workqueue_prep_pwqs() and
drain_workqueues() are removed as the surrounding wq->mutex can
provide sufficient synchronization.

Also, assert_rcu_or_pwq_lock() is renamed to assert_rcu_or_wq_mutex()
and checks for wq->mutex too.

pwq_lock locking and assertion are not removed by this patch and a
couple of for_each_pwq() iterations are still protected by it.
They'll be removed by future patches.

tj: Rebased on top of the current dev branch.  Updated description.
    Folded in assert_rcu_or_wq_mutex() renaming from a later patch
    along with associated comment updates.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
2013-03-25 16:57:18 -07:00
Lai Jiangshan 87fc741e94 workqueue: protect wq->nr_drainers and ->flags with wq->mutex
We're expanding wq->mutex to cover all fields specific to each
workqueue with the end goal of replacing pwq_lock which will make
locking simpler and easier to understand.

wq->nr_drainers and ->flags are specific to each workqueue.  Protect
->nr_drainers and ->flags with wq->mutex instead of pool_mutex.

tj: Rebased on top of the current dev branch.  Updated description.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
2013-03-25 16:57:18 -07:00
Lai Jiangshan 3c25a55daa workqueue: rename wq->flush_mutex to wq->mutex
Currently pwq->flush_mutex protects many fields of a workqueue
including, especially, the pwqs list.  We're going to expand this
mutex to protect most of a workqueue and eventually replace pwq_lock,
which will make locking simpler and easier to understand.

Drop the "flush_" prefix in preparation.

This patch is pure rename.

tj: Rebased on top of the current dev branch.  Updated description.
    Use WQ: and WR: instead of Q: and QR: for synchronization labels.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
2013-03-25 16:57:17 -07:00
Lai Jiangshan 68e13a67dd workqueue: rename wq_mutex to wq_pool_mutex
wq->flush_mutex will be renamed to wq->mutex and cover all fields
specific to each workqueue and eventually replace pwq_lock, which will
make locking simpler and easier to understand.

Rename wq_mutex to wq_pool_mutex to avoid confusion with wq->mutex.
After the scheduled changes, wq_pool_mutex won't be protecting
anything specific to each workqueue instance anyway.

This patch is pure rename.

tj: s/wqs_mutex/wq_pool_mutex/.  Rewrote description.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-25 16:57:17 -07:00
Lai Jiangshan 519e3c1163 workqueue: avoid false negative in assert_manager_or_pool_lock()
If lockdep complains something for other subsystem, lockdep_is_held()
can be false negative, so we need to also test debug_locks before
triggering WARN.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
2013-03-20 11:21:34 -07:00
Lai Jiangshan 881094532e workqueue: use rcu_read_lock_sched() instead for accessing pwq in RCU
rcu_read_lock_sched() is better than preempt_disable() if the code is
protected by RCU_SCHED.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
2013-03-20 11:00:57 -07:00
Lai Jiangshan 951a078a52 workqueue: kick a worker in pwq_adjust_max_active()
If pwq_adjust_max_active() changes max_active from 0 to
saved_max_active, it needs to wakeup worker.  This is already done by
thaw_workqueues().

If pwq_adjust_max_active() increases max_active for an unbound wq,
while not strictly necessary for correctness, it's still desirable to
wake up a worker so that the requested concurrency level is reached
sooner.

Move wake_up_worker() call from thaw_workqueues() to
pwq_adjust_max_active() so that it can handle both of the above two
cases.  This also makes thaw_workqueues() simpler.

tj: Updated comments and description.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
2013-03-20 10:52:30 -07:00
Lai Jiangshan 6a092dfd51 workqueue: simplify current_is_workqueue_rescuer()
We can test worker->recue_wq instead of reaching into
current_pwq->wq->rescuer and then comparing it to self.

tj: Commit message.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
2013-03-20 10:40:25 -07:00
Lai Jiangshan 12ee4fc67c workqueue: add missing POOL_FREEZING
get_unbound_pool() forgot to set POOL_FREEZING if workqueue_freezing
is set and a new pool could go out of sync with the global freezing
state.

Fix it by adding POOL_FREEZING if workqueue_freezing.  wq_mutex is
already held so no further locking is necessary.  This also removes
the unused static variable warning when !CONFIG_FREEZER.

tj: Updated commit message.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
2013-03-20 10:19:09 -07:00
Tejun Heo 7dbc725e47 workqueue: restore CPU affinity of unbound workers on CPU_ONLINE
With the recent addition of the custom attributes support, unbound
pools may have allowed cpumask which isn't full.  As long as some of
CPUs in the cpumask are online, its workers will maintain cpus_allowed
as set on worker creation; however, once no online CPU is left in
cpus_allowed, the scheduler will reset cpus_allowed of any workers
which get scheduled so that they can execute.

To remain compliant to the user-specified configuration, CPU affinity
needs to be restored when a CPU becomes online for an unbound pool
which doesn't currently have any online CPUs before.

This patch implement restore_unbound_workers_cpumask(), which is
called from CPU_ONLINE for all unbound pools, checks whether the
coming up CPU is the first allowed online one, and, if so, invokes
set_cpus_allowed_ptr() with the configured cpumask on all workers.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-19 13:45:21 -07:00
Tejun Heo a9ab775bca workqueue: directly restore CPU affinity of workers from CPU_ONLINE
Rebinding workers of a per-cpu pool after a CPU comes online involves
a lot of back-and-forth mostly because only the task itself could
adjust CPU affinity if PF_THREAD_BOUND was set.

As CPU_ONLINE itself couldn't adjust affinity, it had to somehow
coerce the workers themselves to perform set_cpus_allowed_ptr().  Due
to the various states a worker can be in, this led to three different
paths a worker may be rebound.  worker->rebind_work is queued to busy
workers.  Idle ones are signaled by unlinking worker->entry and call
idle_worker_rebind().  The manager isn't covered by either and
implements its own mechanism.

PF_THREAD_BOUND has been relaced with PF_NO_SETAFFINITY and CPU_ONLINE
itself now can manipulate CPU affinity of workers.  This patch
replaces the existing rebind mechanism with direct one where
CPU_ONLINE iterates over all workers using for_each_pool_worker(),
restores CPU affinity, and clears WORKER_UNBOUND.

There are a couple subtleties.  All bound idle workers should have
their runqueues set to that of the bound CPU; however, if the target
task isn't running, set_cpus_allowed_ptr() just updates the
cpus_allowed mask deferring the actual migration to when the task
wakes up.  This is worked around by waking up idle workers after
restoring CPU affinity before any workers can become bound.

Another subtlety is stems from matching @pool->nr_running with the
number of running unbound workers.  While DISASSOCIATED, all workers
are unbound and nr_running is zero.  As workers become bound again,
nr_running needs to be adjusted accordingly; however, there is no good
way to tell whether a given worker is running without poking into
scheduler internals.  Instead of clearing UNBOUND directly,
rebind_workers() replaces UNBOUND with another new NOT_RUNNING flag -
REBOUND, which will later be cleared by the workers themselves while
preparing for the next round of work item execution.  The only change
needed for the workers is clearing REBOUND along with PREP.

* This patch leaves for_each_busy_worker() without any user.  Removed.

* idle_worker_rebind(), busy_worker_rebind_fn(), worker->rebind_work
  and rebind logic in manager_workers() removed.

* worker_thread() now looks at WORKER_DIE instead of testing whether
  @worker->entry is empty to determine whether it needs to do
  something special as dying is the only special thing now.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-19 13:45:21 -07:00
Tejun Heo bd7c089eb2 workqueue: relocate rebind_workers()
rebind_workers() will be reimplemented in a way which makes it mostly
decoupled from the rest of worker management.  Move rebind_workers()
so that it's located with other CPU hotplug related functions.

This patch is pure function relocation.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-19 13:45:21 -07:00
Tejun Heo 822d8405d1 workqueue: convert worker_pool->worker_ida to idr and implement for_each_pool_worker()
Make worker_ida an idr - worker_idr and use it to implement
for_each_pool_worker() which will be used to simplify worker rebinding
on CPU_ONLINE.

pool->worker_idr is protected by both pool->manager_mutex and
pool->lock so that it can be iterated while holding either lock.

* create_worker() allocates ID without installing worker pointer and
  installs the pointer later using idr_replace().  This is because
  worker ID is needed when creating the actual task to name it and the
  new worker shouldn't be visible to iterations before fully
  initialized.

* In destroy_worker(), ID removal is moved before kthread_stop().
  This is again to guarantee that only fully working workers are
  visible to for_each_pool_worker().

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2013-03-19 13:45:21 -07:00
Tejun Heo 14a40ffccd sched: replace PF_THREAD_BOUND with PF_NO_SETAFFINITY
PF_THREAD_BOUND was originally used to mark kernel threads which were
bound to a specific CPU using kthread_bind() and a task with the flag
set allows cpus_allowed modifications only to itself.  Workqueue is
currently abusing it to prevent userland from meddling with
cpus_allowed of workqueue workers.

What we need is a flag to prevent userland from messing with
cpus_allowed of certain kernel tasks.  In kernel, anyone can
(incorrectly) squash the flag, and, for worker-type usages,
restricting cpus_allowed modification to the task itself doesn't
provide meaningful extra proection as other tasks can inject work
items to the task anyway.

This patch replaces PF_THREAD_BOUND with PF_NO_SETAFFINITY.
sched_setaffinity() checks the flag and return -EINVAL if set.
set_cpus_allowed_ptr() is no longer affected by the flag.

This will allow simplifying workqueue worker CPU affinity management.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
2013-03-19 13:45:20 -07:00
Linus Torvalds b63dc123b2 Merge branch 'for-3.9-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq
Pull workqueue fix from Tejun Heo:
 "Lai's patch to fix highly unlikely but still possible workqueue stall
  during CPU hotunplug."

* 'for-3.9-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq:
  workqueue: fix possible pool stall bug in wq_unbind_fn()
2013-03-18 18:47:07 -07:00
Tejun Heo 2e109a2855 workqueue: rename workqueue_lock to wq_mayday_lock
With the recent locking updates, the only thing protected by
workqueue_lock is workqueue->maydays list.  Rename workqueue_lock to
wq_mayday_lock.

This patch is pure rename.

Signed-off-by: Tejun Heo <tj@kernel.org>
2013-03-13 19:47:40 -07:00
Tejun Heo 794b18bc8a workqueue: separate out pool_workqueue locking into pwq_lock
This patch continues locking cleanup from the previous patch.  It
breaks out pool_workqueue synchronization from workqueue_lock into a
new spinlock - pwq_lock.  The followings are protected by pwq_lock.

* workqueue->pwqs
* workqueue->saved_max_active

The conversion is straight-forward.  workqueue_lock usages which cover
the above two are converted to pwq_lock.  New locking label PW added
for things protected by pwq_lock and FR is updated to mean flush_mutex
+ pwq_lock + sched-RCU.

This patch shouldn't introduce any visible behavior changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
2013-03-13 19:47:40 -07:00
Tejun Heo 5bcab3355a workqueue: separate out pool and workqueue locking into wq_mutex
Currently, workqueue_lock protects most shared workqueue resources -
the pools, workqueues, pool_workqueues, draining, ID assignments,
mayday handling and so on.  The coverage has grown organically and
there is no identified bottleneck coming from workqueue_lock, but it
has grown a bit too much and scheduled rebinding changes need the
pools and workqueues to be protected by a mutex instead of a spinlock.

This patch breaks out pool and workqueue synchronization from
workqueue_lock into a new mutex - wq_mutex.  The followings are
protected by wq_mutex.

* worker_pool_idr and unbound_pool_hash
* pool->refcnt
* workqueues list
* workqueue->flags, ->nr_drainers

Most changes are mostly straight-forward.  workqueue_lock is replaced
with wq_mutex where applicable and workqueue_lock lock/unlocks are
added where wq_mutex conversion leaves data structures not protected
by wq_mutex without locking.  irq / preemption flippings were added
where the conversion affects them.  Things worth noting are

* New WQ and WR locking lables added along with
  assert_rcu_or_wq_mutex().

* worker_pool_assign_id() now expects to be called under wq_mutex.

* create_mutex is removed from get_unbound_pool().  It now just holds
  wq_mutex.

This patch shouldn't introduce any visible behavior changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
2013-03-13 19:47:40 -07:00
Tejun Heo 7d19c5ce66 workqueue: relocate global variable defs and function decls in workqueue.c
They're split across debugobj code for some reason.  Collect them.

This patch is pure relocation.

Signed-off-by: Tejun Heo <tj@kernel.org>
2013-03-13 19:47:40 -07:00
Tejun Heo cd549687a7 workqueue: better define locking rules around worker creation / destruction
When a manager creates or destroys workers, the operations are always
done with the manager_mutex held; however, initial worker creation or
worker destruction during pool release don't grab the mutex.  They are
still correct as initial worker creation doesn't require
synchronization and grabbing manager_arb provides enough exclusion for
pool release path.

Still, let's make everyone follow the same rules for consistency and
such that lockdep annotations can be added.

Update create_and_start_worker() and put_unbound_pool() to grab
manager_mutex around thread creation and destruction respectively and
add lockdep assertions to create_worker() and destroy_worker().

This patch doesn't introduce any visible behavior changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
2013-03-13 19:47:39 -07:00
Tejun Heo ebf44d16ec workqueue: factor out initial worker creation into create_and_start_worker()
get_unbound_pool(), workqueue_cpu_up_callback() and init_workqueues()
have similar code pieces to create and start the initial worker factor
those out into create_and_start_worker().

This patch doesn't introduce any functional changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
2013-03-13 19:47:39 -07:00
Tejun Heo bc3a1afc92 workqueue: rename worker_pool->assoc_mutex to ->manager_mutex
Manager operations are currently governed by two mutexes -
pool->manager_arb and ->assoc_mutex.  The former is used to decide who
gets to be the manager and the latter to exclude the actual manager
operations including creation and destruction of workers.  Anyone who
grabs ->manager_arb must perform manager role; otherwise, the pool
might stall.

Grabbing ->assoc_mutex blocks everyone else from performing manager
operations but doesn't require the holder to perform manager duties as
it's merely blocking manager operations without becoming the manager.

Because the blocking was necessary when [dis]associating per-cpu
workqueues during CPU hotplug events, the latter was named
assoc_mutex.  The mutex is scheduled to be used for other purposes, so
this patch gives it a more fitting generic name - manager_mutex - and
updates / adds comments to explain synchronization around the manager
role and operations.

This patch is pure rename / doc update.

Signed-off-by: Tejun Heo <tj@kernel.org>
2013-03-13 19:47:39 -07:00
Tejun Heo 8425e3d5bd workqueue: inline trivial wrappers
There's no reason to make these trivial wrappers full (exported)
functions.  Inline the followings.

 queue_work()
 queue_delayed_work()
 mod_delayed_work()
 schedule_work_on()
 schedule_work()
 schedule_delayed_work_on()
 schedule_delayed_work()
 keventd_up()

Signed-off-by: Tejun Heo <tj@kernel.org>
2013-03-13 16:51:36 -07:00
Tejun Heo 611c92a020 workqueue: rename @id to @pi in for_each_each_pool()
Rename @id argument of for_each_pool() to @pi so that it doesn't get
reused accidentally when for_each_pool() is used in combination with
other iterators.

This patch is purely cosmetic.

Signed-off-by: Tejun Heo <tj@kernel.org>
2013-03-13 16:51:36 -07:00
Tejun Heo c5aa87bbf4 workqueue: update comments and a warning message
* Update incorrect and add missing synchronization labels.

* Update incorrect or misleading comments.  Add new comments where
  clarification is necessary.  Reformat / rephrase some comments.

* drain_workqueue() can be used separately from destroy_workqueue()
  but its warning message was incorrectly referring to destruction.

Other than the warning message change, this patch doesn't make any
functional changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
2013-03-13 16:51:36 -07:00
Tejun Heo 983ca25e73 workqueue: fix max_active handling in init_and_link_pwq()
Since 9e8cd2f589 ("workqueue: implement apply_workqueue_attrs()"),
init_and_link_pwq() may be called to initialize a new pool_workqueue
for a workqueue which is already online, but the function was setting
pwq->max_active to wq->saved_max_active without proper
synchronization.

Fix it by calling pwq_adjust_max_active() under proper locking instead
of manually setting max_active.

Signed-off-by: Tejun Heo <tj@kernel.org>
2013-03-13 16:51:35 -07:00
Tejun Heo 699ce097ef workqueue: implement and use pwq_adjust_max_active()
Rename pwq_set_max_active() to pwq_adjust_max_active() and move
pool_workqueue->max_active synchronization and max_active
determination logic into it.

The new function should be called with workqueue_lock held for stable
workqueue->saved_max_active, determines the current max_active value
the target pool_workqueue should be using from @wq->saved_max_active
and the state of the associated pool, and applies it with proper
synchronization.

The current two users - workqueue_set_max_active() and
thaw_workqueues() - are updated accordingly.  In addition, the manual
freezing handling in __alloc_workqueue_key() and
freeze_workqueues_begin() are replaced with calls to
pwq_adjust_max_active().

This centralizes max_active handling so that it's less error-prone.

Signed-off-by: Tejun Heo <tj@kernel.org>
2013-03-13 16:51:35 -07:00