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authorPeter Zijlstra <peterz@infradead.org>2017-08-23 13:23:30 +0200
committerIngo Molnar <mingo@kernel.org>2017-08-25 11:06:33 +0200
commite6f3faa734a00c606b7b06c6b9f15e5627d3245b (patch)
tree4c3f0047d1fa1796442512e03147c40c026f25a8 /Documentation/atomic_t.txt
parenta1d14934ea4b9db816a8dbfeab1c3e7204a0d871 (diff)
locking/lockdep: Fix workqueue crossrelease annotation
The new completion/crossrelease annotations interact unfavourable with the extant flush_work()/flush_workqueue() annotations. The problem is that when a single work class does: wait_for_completion(&C) and complete(&C) in different executions, we'll build dependencies like: lock_map_acquire(W) complete_acquire(C) and lock_map_acquire(W) complete_release(C) which results in the dependency chain: W->C->W, which lockdep thinks spells deadlock, even though there is no deadlock potential since works are ran concurrently. One possibility would be to change the work 'lock' to recursive-read, but that would mean hitting a lockdep limitation on recursive locks. Also, unconditinoally switching to recursive-read here would fail to detect the actual deadlock on single-threaded workqueues, which do have a problem with this. For now, forcefully disregard these locks for crossrelease. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Tejun Heo <tj@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: boqun.feng@gmail.com Cc: byungchul.park@lge.com Cc: david@fromorbit.com Cc: johannes@sipsolutions.net Cc: oleg@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
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