workqueue/lockdep: 'Fix' flush_work() annotation
The flush_work() annotation as introduced by commit: e159489b ("workqueue: relax lockdep annotation on flush_work()") hits on the lockdep problem with recursive read locks. The situation as described is: Work W1: Work W2: Task: ARR(Q) ARR(Q) flush_workqueue(Q) A(W1) A(W2) A(Q) flush_work(W2) R(Q) A(W2) R(W2) if (special) A(Q) else ARR(Q) R(Q) where: A - acquire, ARR - acquire-read-recursive, R - release. Where under 'special' conditions we want to trigger a lock recursion deadlock, but otherwise allow the flush_work(). The allowing is done by using recursive read locks (ARR), but lockdep is broken for recursive stuff. However, there appears to be no need to acquire the lock if we're not 'special', so if we remove the 'else' clause things become much simpler and no longer need the recursion thing at all. 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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