Commit 87915adc authored Aug 22, 2018 by Johannes Berg Committed by Tejun Heo Aug 22, 2018

workqueue: re-add lockdep dependencies for flushing



In flush_work(), we need to create a lockdep dependency so that
the following scenario is appropriately tagged as a problem:

  work_function()
  {
    mutex_lock(&mutex);
    ...
  }

  other_function()
  {
    mutex_lock(&mutex);
    flush_work(&work); // or cancel_work_sync(&work);
  }

This is a problem since the work might be running and be blocked
on trying to acquire the mutex.

Similarly, in flush_workqueue().

These were removed after cross-release partially caught these
problems, but now cross-release was reverted anyway. IMHO the
removal was erroneous anyway though, since lockdep should be
able to catch potential problems, not just actual ones, and
cross-release would only have caught the problem when actually
invoking wait_for_completion().

Fixes: fd1a5b04 ("workqueue: Remove now redundant lock acquisitions wrt. workqueue flushes")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

parent d6e89786

kernel/workqueue.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -2652,6 +2652,9 @@ void flush_workqueue(struct workqueue_struct *wq)
		if (WARN_ON(!wq_online))
		return;

		lock_map_acquire(&wq->lockdep_map);
		lock_map_release(&wq->lockdep_map);

		mutex_lock(&wq->mutex);

		/*
		@@ -2905,6 +2908,11 @@ static bool __flush_work(struct work_struct *work, bool from_cancel)
		if (WARN_ON(!wq_online))
		return false;

		if (!from_cancel) {
		lock_map_acquire(&work->lockdep_map);
		lock_map_release(&work->lockdep_map);
		}

		if (start_flush_work(work, &barr, from_cancel)) {
		wait_for_completion(&barr.done);
		destroy_work_on_stack(&barr.work);

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