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由 Tejun Heo 提交于
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 held. Unlocking mutex while holding an irq spinlock was never safe and this problem has been around forever but it never got noticed because the only time the mutex is usually trylocked while holding irqlock making actual failures very unlikely and lockdep annotation missed the condition until the recent b9c16a0e ("locking/mutex: Fix lockdep_assert_held() fail"). Using mutex for pool->manager_arb has always been a bit of stretch. It primarily is an mechanism to arbitrate managership between workers which can easily be done with a pool flag. The only reason it became a mutex is that pool destruction path wants to exclude parallel managing operations. This patch replaces the mutex with a new pool flag POOL_MANAGER_ACTIVE and make the destruction path wait for the current manager on a wait queue. v2: Drop unnecessary flag clearing before pool destruction as suggested by Boqun. Signed-off-by: NTejun Heo <tj@kernel.org> Reported-by: NJosef Bacik <josef@toxicpanda.com> Reviewed-by: NLai Jiangshan <jiangshanlai@gmail.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Boqun Feng <boqun.feng@gmail.com> Cc: stable@vger.kernel.org
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