Messages in this thread |  | | Date | Sun, 8 Oct 2017 12:03:47 -0700 | From | Tejun Heo <> | Subject | Re: [RFC] workqueue: Fix irq inversion deadlock in manage_workers() |
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Hello, Boqun.
On Sun, Oct 08, 2017 at 05:02:23PM +0800, Boqun Feng wrote: > Josef reported a HARDIRQ-safe -> HARDIRQ-unsafe lock order detected by > lockdep: > > | [ 1270.472259] WARNING: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected > | [ 1270.472783] 4.14.0-rc1-xfstests-12888-g76833e8 #110 Not tainted > | [ 1270.473240] ----------------------------------------------------- > | [ 1270.473710] kworker/u5:2/5157 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire: > | [ 1270.474239] (&(&lock->wait_lock)->rlock){+.+.}, at: [<ffffffff8da253d2>] __mutex_unlock_slowpath+0xa2/0x280 > | [ 1270.474994] > | [ 1270.474994] and this task is already holding: > | [ 1270.475440] (&pool->lock/1){-.-.}, at: [<ffffffff8d2992f6>] worker_thread+0x366/0x3c0 > | [ 1270.476046] which would create a new lock dependency: > | [ 1270.476436] (&pool->lock/1){-.-.} -> (&(&lock->wait_lock)->rlock){+.+.} > | [ 1270.476949] > | [ 1270.476949] but this new dependency connects a HARDIRQ-irq-safe lock: > | [ 1270.477553] (&pool->lock/1){-.-.} > ... > | [ 1270.488900] to a HARDIRQ-irq-unsafe lock: > | [ 1270.489327] (&(&lock->wait_lock)->rlock){+.+.} > ... > | [ 1270.494735] Possible interrupt unsafe locking scenario: > | [ 1270.494735] > | [ 1270.495250] CPU0 CPU1 > | [ 1270.495600] ---- ---- > | [ 1270.495947] lock(&(&lock->wait_lock)->rlock); > | [ 1270.496295] local_irq_disable(); > | [ 1270.496753] lock(&pool->lock/1); > | [ 1270.497205] lock(&(&lock->wait_lock)->rlock); > | [ 1270.497744] <Interrupt> > | [ 1270.497948] lock(&pool->lock/1); > > , which will cause a irq inversion deadlock if the above lock scenario > happens. > > The root cause of this safe -> unsafe lock order is the > mutex_unlock(pool::manager_arb) in manage_workers() with pool::lock
So, if I'm not mistaken, this is a regression caused by b9c16a0e1f73 ("locking/mutex: Fix lockdep_assert_held() fail") which seems to replace irqsave operations inside mutex to unconditional irq ones.
I suppose it's a requirement we can add but that needs to be an explicit change with backing rationales.
Thanks.
-- tejun
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