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db751fe3ea
After adding lockdep support to seqlock/seqcount structures, I started seeing the following warning: [ 1.070907] ====================================================== [ 1.072015] [ INFO: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected ] [ 1.073181] 3.11.0+ #67 Not tainted [ 1.073801] ------------------------------------------------------ [ 1.074882] kworker/u4:2/708 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire: [ 1.076088] (&p->mems_allowed_seq){+.+...}, at: [<ffffffff81187d7f>] new_slab+0x5f/0x280 [ 1.077572] [ 1.077572] and this task is already holding: [ 1.078593] (&(&q->__queue_lock)->rlock){..-...}, at: [<ffffffff81339f03>] blk_execute_rq_nowait+0x53/0xf0 [ 1.080042] which would create a new lock dependency: [ 1.080042] (&(&q->__queue_lock)->rlock){..-...} -> (&p->mems_allowed_seq){+.+...} [ 1.080042] [ 1.080042] but this new dependency connects a SOFTIRQ-irq-safe lock: [ 1.080042] (&(&q->__queue_lock)->rlock){..-...} [ 1.080042] ... which became SOFTIRQ-irq-safe at: [ 1.080042] [<ffffffff810ec179>] __lock_acquire+0x5b9/0x1db0 [ 1.080042] [<ffffffff810edfe5>] lock_acquire+0x95/0x130 [ 1.080042] [<ffffffff818968a1>] _raw_spin_lock+0x41/0x80 [ 1.080042] [<ffffffff81560c9e>] scsi_device_unbusy+0x7e/0xd0 [ 1.080042] [<ffffffff8155a612>] scsi_finish_command+0x32/0xf0 [ 1.080042] [<ffffffff81560e91>] scsi_softirq_done+0xa1/0x130 [ 1.080042] [<ffffffff8133b0f3>] blk_done_softirq+0x73/0x90 [ 1.080042] [<ffffffff81095dc0>] __do_softirq+0x110/0x2f0 [ 1.080042] [<ffffffff81095fcd>] run_ksoftirqd+0x2d/0x60 [ 1.080042] [<ffffffff810bc506>] smpboot_thread_fn+0x156/0x1e0 [ 1.080042] [<ffffffff810b3916>] kthread+0xd6/0xe0 [ 1.080042] [<ffffffff818980ac>] ret_from_fork+0x7c/0xb0 [ 1.080042] [ 1.080042] to a SOFTIRQ-irq-unsafe lock: [ 1.080042] (&p->mems_allowed_seq){+.+...} [ 1.080042] ... which became SOFTIRQ-irq-unsafe at: [ 1.080042] ... [<ffffffff810ec1d3>] __lock_acquire+0x613/0x1db0 [ 1.080042] [<ffffffff810edfe5>] lock_acquire+0x95/0x130 [ 1.080042] [<ffffffff810b3df2>] kthreadd+0x82/0x180 [ 1.080042] [<ffffffff818980ac>] ret_from_fork+0x7c/0xb0 [ 1.080042] [ 1.080042] other info that might help us debug this: [ 1.080042] [ 1.080042] Possible interrupt unsafe locking scenario: [ 1.080042] [ 1.080042] CPU0 CPU1 [ 1.080042] ---- ---- [ 1.080042] lock(&p->mems_allowed_seq); [ 1.080042] local_irq_disable(); [ 1.080042] lock(&(&q->__queue_lock)->rlock); [ 1.080042] lock(&p->mems_allowed_seq); [ 1.080042] <Interrupt> [ 1.080042] lock(&(&q->__queue_lock)->rlock); [ 1.080042] [ 1.080042] *** DEADLOCK *** The issue stems from the kthreadd() function calling set_mems_allowed with irqs enabled. While its possibly unlikely for the actual deadlock to trigger, a fix is fairly simple: disable irqs before taking the mems_allowed_seq lock. Signed-off-by: John Stultz <john.stultz@linaro.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Li Zefan <lizefan@huawei.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: "David S. Miller" <davem@davemloft.net> Cc: netdev@vger.kernel.org Link: http://lkml.kernel.org/r/1381186321-4906-4-git-send-email-john.stultz@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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