Re: [2.6.31-rc9] hotplug SATA vs lockdep: false positive?
From: Peter Zijlstra
Date: Thu Sep 10 2009 - 11:43:31 EST
On Wed, 2009年09月09日 at 22:20 +0100, Daniel J Blueman wrote:
>
When hot-plugging my SATA DVD drive into my laptop, I see a lockdep
>
warning [1]. On closer inspection, both flush_workqueue() and
>
worker_thread() do tricks with lockdep maps. False positive?
No, looks like a typical case of a workqueue trying to flush itself,
something that can easily deadlock for real.
>
=======================================================
>
[ INFO: possible circular locking dependency detected ]
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2.6.31-rc9-290cd #1
>
-------------------------------------------------------
>
kacpi_hotplug/198 is trying to acquire lock:
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(kacpid){+.+.+.}, at: [<ffffffff81073a70>] flush_workqueue+0x0/0xf0
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(workqueue.c:292)
>
>
but task is already holding lock:
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(&dpc->work){+.+.+.}, at: [<ffffffff81072a42>]
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worker_thread+0x1f2/0x3c0 (bitops.h:101)
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which lock already depends on the new lock.
>
>
the existing dependency chain (in reverse order) is:
>
>
-> #1 (&dpc->work){+.+.+.}:
>
[<ffffffff8108eb19>] __lock_acquire+0xe29/0x1240
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[<ffffffff8108f04e>] lock_acquire+0x11e/0x170
>
[<ffffffff81072a92>] worker_thread+0x242/0x3c0 (workqueue.c:291)
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[<ffffffff81077456>] kthread+0xa6/0xc0
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[<ffffffff8100d29a>] child_rip+0xa/0x20
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[<ffffffffffffffff>] 0xffffffffffffffff
>
>
-> #0 (kacpid){+.+.+.}:
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[<ffffffff8108ebe1>] __lock_acquire+0xef1/0x1240
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[<ffffffff8108f04e>] lock_acquire+0x11e/0x170
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[<ffffffff81073acc>] flush_workqueue+0x5c/0xf0 (workqueue.c:403)
>
[<ffffffff812f6eaf>] acpi_os_wait_events_complete+0x10/0x1e
>
[<ffffffff812f6ee7>] acpi_os_execute_hp_deferred+0x2a/0x3e
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[<ffffffff81072a98>] worker_thread+0x248/0x3c0 (workqueue.c:292)
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[<ffffffff81077456>] kthread+0xa6/0xc0
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[<ffffffff8100d29a>] child_rip+0xa/0x20
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[<ffffffffffffffff>] 0xffffffffffffffff
>
>
other info that might help us debug this:
>
>
2 locks held by kacpi_hotplug/198:
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#0: (kacpi_hotplug){+.+...}, at: [<ffffffff81072a42>]
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worker_thread+0x1f2/0x3c0
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#1: (&dpc->work){+.+.+.}, at: [<ffffffff81072a42>] worker_thread+0x1f2/0x3c0
>
>
stack backtrace:
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Pid: 198, comm: kacpi_hotplug Tainted: G C 2.6.31-rc9-290cd #1
>
>
Call Trace:
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[<ffffffff8108c8a7>] print_circular_bug_tail+0xa7/0x100
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[<ffffffff8108ebe1>] __lock_acquire+0xef1/0x1240
>
[<ffffffff8108a808>] ? add_lock_to_list+0x58/0xf0
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[<ffffffff8108f04e>] lock_acquire+0x11e/0x170
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[<ffffffff81073a70>] ? flush_workqueue+0x0/0xf0 (workqueue.c:397)
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[<ffffffff812f6ebd>] ? acpi_os_execute_hp_deferred+0x0/0x3e
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[<ffffffff81073acc>] flush_workqueue+0x5c/0xf0 (workqueue.c:403)
>
[<ffffffff81073a70>] ? flush_workqueue+0x0/0xf0 (workqueue.c:397)
>
[<ffffffff812f6eaf>] acpi_os_wait_events_complete+0x10/0x1e drivers/acpi/osl.c
>
[<ffffffff812f6ee7>] acpi_os_execute_hp_deferred+0x2a/0x3e
>
[<ffffffff81072a98>] worker_thread+0x248/0x3c0 (workqueue.c:292)
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[<ffffffff81072a42>] ? worker_thread+0x1f2/0x3c0
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[<ffffffff81077900>] ? autoremove_wake_function+0x0/0x40
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[<ffffffff81072850>] ? worker_thread+0x0/0x3c0
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[<ffffffff81077456>] kthread+0xa6/0xc0
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[<ffffffff8100d29a>] child_rip+0xa/0x20
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[<ffffffff8100cbd4>] ? restore_args+0x0/0x30
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[<ffffffff810773b0>] ? kthread+0x0/0xc0
>
[<ffffffff8100d290>] ? child_rip+0x0/0x20
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