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
