linux-stable.git/kernel/workqueue.c, branch v3.5.3

workqueue: perform cpu down operations from low priority cpu_notifier()

2012-08-09T15:22:54+00:00

commit 6575820221f7a4dd6eadecf7bf83cdd154335eda upstream.

Currently, all workqueue cpu hotplug operations run off
CPU_PRI_WORKQUEUE which is higher than normal notifiers.  This is to
ensure that workqueue is up and running while bringing up a CPU before
other notifiers try to use workqueue on the CPU.

Per-cpu workqueues are supposed to remain working and bound to the CPU
for normal CPU_DOWN_PREPARE notifiers.  This holds mostly true even
with workqueue offlining running with higher priority because
workqueue CPU_DOWN_PREPARE only creates a bound trustee thread which
runs the per-cpu workqueue without concurrency management without
explicitly detaching the existing workers.

However, if the trustee needs to create new workers, it creates
unbound workers which may wander off to other CPUs while
CPU_DOWN_PREPARE notifiers are in progress.  Furthermore, if the CPU
down is cancelled, the per-CPU workqueue may end up with workers which
aren't bound to the CPU.

While reliably reproducible with a convoluted artificial test-case
involving scheduling and flushing CPU burning work items from CPU down
notifiers, this isn't very likely to happen in the wild, and, even
when it happens, the effects are likely to be hidden by the following
successful CPU down.

Fix it by using different priorities for up and down notifiers - high
priority for up operations and low priority for down operations.

Workqueue cpu hotplug operations will soon go through further cleanup.

Signed-off-by: Tejun Heo 
Acked-by: "Rafael J. Wysocki" 
Signed-off-by: Greg Kroah-Hartman

lockdep: fix oops in processing workqueue

2012-05-15T15:08:31+00:00

Under memory load, on x86_64, with lockdep enabled, the workqueue's
process_one_work() has been seen to oops in __lock_acquire(), barfing
on a 0xffffffff00000000 pointer in the lockdep_map's class_cache[].

Because it's permissible to free a work_struct from its callout function,
the map used is an onstack copy of the map given in the work_struct: and
that copy is made without any locking.

Surprisingly, gcc (4.5.1 in Hugh's case) uses "rep movsl" rather than
"rep movsq" for that structure copy: which might race with a workqueue
user's wait_on_work() doing lock_map_acquire() on the source of the
copy, putting a pointer into the class_cache[], but only in time for
the top half of that pointer to be copied to the destination map.

Boom when process_one_work() subsequently does lock_map_acquire()
on its onstack copy of the lockdep_map.

Fix this, and a similar instance in call_timer_fn(), with a
lockdep_copy_map() function which additionally NULLs the class_cache[].

Note: this oops was actually seen on 3.4-next, where flush_work() newly
does the racing lock_map_acquire(); but Tejun points out that 3.4 and
earlier are already vulnerable to the same through wait_on_work().

* Patch orginally from Peter.  Hugh modified it a bit and wrote the
  description.

Signed-off-by: Peter Zijlstra 
Reported-by: Hugh Dickins 
LKML-Reference: 
Signed-off-by: Tejun Heo

workqueue: skip nr_running sanity check in worker_enter_idle() if trustee is active

2012-05-14T22:04:50+00:00

worker_enter_idle() has WARN_ON_ONCE() which triggers if nr_running
isn't zero when every worker is idle.  This can trigger spuriously
while a cpu is going down due to the way trustee sets %WORKER_ROGUE
and zaps nr_running.

It first sets %WORKER_ROGUE on all workers without updating
nr_running, releases gcwq->lock, schedules, regrabs gcwq->lock and
then zaps nr_running.  If the last running worker enters idle
inbetween, it would see stale nr_running which hasn't been zapped yet
and trigger the WARN_ON_ONCE().

Fix it by performing the sanity check iff the trustee is idle.

Signed-off-by: Tejun Heo 
Reported-by: "Paul E. McKenney" 
Cc: stable@vger.kernel.org

workqueue: Catch more locking problems with flush_work()

2012-04-23T18:06:42+00:00

If a workqueue is flushed with flush_work() lockdep checking can
be circumvented. For example:

 static DEFINE_MUTEX(mutex);

 static void my_work(struct work_struct *w)
 {
         mutex_lock(&mutex);
         mutex_unlock(&mutex);
 }

 static DECLARE_WORK(work, my_work);

 static int __init start_test_module(void)
 {
         schedule_work(&work);
         return 0;
 }
 module_init(start_test_module);

 static void __exit stop_test_module(void)
 {
         mutex_lock(&mutex);
         flush_work(&work);
         mutex_unlock(&mutex);
 }
 module_exit(stop_test_module);

would not always print a warning when flush_work() was called.
In this trivial example nothing could go wrong since we are
guaranteed module_init() and module_exit() don't run concurrently,
but if the work item is schedule asynchronously we could have a
scenario where the work item is running just at the time flush_work()
is called resulting in a classic ABBA locking problem.

Add a lockdep hint by acquiring and releasing the work item
lockdep_map in flush_work() so that we always catch this
potential deadlock scenario.

Signed-off-by: Stephen Boyd 
Reviewed-by: Yong Zhang 
Signed-off-by: Tejun Heo

workqueue: change BUG_ON() to WARN_ON()

2012-04-16T21:54:59+00:00

This BUG_ON() can be triggered if you call schedule_work() before
calling INIT_WORK().  It is a bug definitely, but it's nicer to just
print a stack trace and return.

Reported-by: Matt Renzelmann 
Signed-off-by: Dan Carpenter 
Signed-off-by: Tejun Heo

Merge branch 'for-3.4' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq

2012-03-21T01:13:22+00:00

Pull workqueue changes from Tejun Heo:
 "This contains only one commit which cleans up UP allocation path a
  bit."

* 'for-3.4' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq:
  workqueue: use percpu allocator for cwq on UP

workqueue: use percpu allocator for cwq on UP

2012-03-12T16:21:17+00:00

I notice that the commit bbddff makes percpu allocator can work on UP,
So we don't need the magic way for UP.

Signed-off-by: Lai Jiangshan 
Signed-off-by: Tejun Heo

Block: use a freezable workqueue for disk-event polling

2012-03-02T09:51:00+00:00

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 
CC: 
Acked-by: Tejun Heo 
Acked-by: Rafael J. Wysocki 
Signed-off-by: Jens Axboe

workqueue: make alloc_workqueue() take printf fmt and args for name

2012-01-11T00:30:54+00:00

alloc_workqueue() currently expects the passed in @name pointer to remain
accessible.  This is inconvenient and a bit silly given that the whole wq
is being dynamically allocated.  This patch updates alloc_workqueue() and
friends to take printf format string instead of opaque string and matching
varargs at the end.  The name is allocated together with the wq and
formatted.

alloc_ordered_workqueue() is converted to a macro to unify varargs
handling with alloc_workqueue(), and, while at it, add comment to
alloc_workqueue().

None of the current in-kernel users pass in string with '%' as constant
name and this change shouldn't cause any problem.

[akpm@linux-foundation.org: use __printf]
Signed-off-by: Tejun Heo 
Suggested-by: Christoph Hellwig 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

kernel: Map most files to use export.h instead of module.h

2011-10-31T13:20:12+00:00

The changed files were only including linux/module.h for the
EXPORT_SYMBOL infrastructure, and nothing else.  Revector them
onto the isolated export header for faster compile times.

Nothing to see here but a whole lot of instances of:

  -#include 
  +#include 

This commit is only changing the kernel dir; next targets
will probably be mm, fs, the arch dirs, etc.

Signed-off-by: Paul Gortmaker