Merge branch 'for-3.19-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq

Pull workqueue fix from Tejun Heo:
 "The xfs folks have been running into weird and very rare lockups for
  some time now.  I didn't think this could have been from workqueue
  side because no one else was reporting it.  This time, Eric had a
  kdump which we looked into and it turned out this actually was a
  workqueue bug and the bug has been there since the beginning of
  concurrency managed workqueue.

  A worker pool ensures forward progress of the workqueues associated
  with it by always having at least one worker reserved from executing
  work items.  When the pool is under contention, the idle one tries to
  create more workers for the pool and if that doesn't succeed quickly
  enough, it calls the rescuers to the pool.

  This logic had a subtle race condition in an early exit path.  When a
  worker invokes this manager function, the function may return %false
  indicating that the caller may proceed to executing work items either
  because another worker is already performing the role or conditions
  have changed and the pool is no longer under contention.

  The latter part depended on the assumption that whether more workers
  are necessary or not remains stable while the pool is locked; however,
  pool->nr_running (concurrency count) may change asynchronously and it
  getting bumped from zero asynchronously could send off the last idle
  worker to execute work items.

  The race window is fairly narrow, and, even when it gets triggered,
  the pool deadlocks iff if all work items get blocked on pending work
  items of the pool, which is highly unlikely but can be triggered by
  xfs.

  The patch removes the race window by removing the early exit path,
  which doesn't server any purpose anymore anyway"

* 'for-3.19-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq:
  workqueue: fix subtle pool management issue which can stall whole worker_pool

0 files changed, 0 insertions, 0 deletions