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Date: Wed, 26 May 2010 10:40:22 +0800
From: Yang Ruirui <ruirui.r.yang@...to.com>
To: <linux-kernel@...r.kernel.org>
CC: <hidave.darkstar@...il.com>, <fengguang.wu@...el.com>
Subject: sysrq+s lockdep warning
Hi,
sysrq emergency sync triggered following lockdep warning, how to deal with it?
The emergency sync is in a work queue now, but consider it's "emergency", how about directly call sync functions instead of put them into work queue?
[19985.379671] SysRq : Emergency Sync
[19987.539673] SysRq : Emergency Sync
[19994.937853]
[19994.937854] =======================================================
[19994.937857] [ INFO: possible circular locking dependency detected ]
[19994.937859] 2.6.34-07097-gf4b87de-dirty #32
[19994.937861] -------------------------------------------------------
[19994.937862] events/0/7 is trying to acquire lock:
[19994.937864] (&type->s_umount_key#19){++++..}, at: [<ffffffff810e729e>] iterate_supers+0x5d/0xb2
[19994.937872]
[19994.937873] but task is already holding lock:
[19994.937874] ((work)#3){+.+...}, at: [<ffffffff8104b5d0>] worker_thread+0x1d5/0x332
[19994.937880]
[19994.937881] which lock already depends on the new lock.
[19994.937881]
[19994.937883]
[19994.937883] the existing dependency chain (in reverse order) is:
[19994.937885]
[19994.937885] -> #3 ((work)#3){+.+...}:
[19994.937889] [<ffffffff81061bff>] lock_acquire+0xd2/0xfe
[19994.937892] [<ffffffff8104b61e>] worker_thread+0x223/0x332
[19994.937895] [<ffffffff8104f0ee>] kthread+0x7d/0x85
[19994.937898] [<ffffffff81003844>] kernel_thread_helper+0x4/0x10
[19994.937902]
[19994.937903] -> #2 (events){+.+.+.}:
[19994.937906] [<ffffffff81061bff>] lock_acquire+0xd2/0xfe
[19994.937909] [<ffffffff8104c1e3>] flush_work+0x67/0xf2
[19994.937911] [<ffffffff8104c39c>] schedule_on_each_cpu+0x12e/0x16d
[19994.937914] [<ffffffff810b8c9f>] lru_add_drain_all+0x10/0x12
[19994.937918] [<ffffffff811079c2>] invalidate_bdev+0x36/0x49
[19994.937922] [<ffffffff8116a5a9>] ext4_put_super+0x28a/0x317
[19994.937926] [<ffffffff810e80e5>] generic_shutdown_super+0x51/0xd2
[19994.937929] [<ffffffff810e8188>] kill_block_super+0x22/0x3a
[19994.937932] [<ffffffff810e752f>] deactivate_locked_super+0x3d/0x5d
[19994.937934] [<ffffffff810e798e>] deactivate_super+0x40/0x44
[19994.937937] [<ffffffff810fbed4>] mntput_no_expire+0xbb/0xf0
[19994.937941] [<ffffffff810fc48f>] sys_umount+0x2cf/0x2fa
[19994.937943] [<ffffffff810029c2>] system_call_fastpath+0x16/0x1b
[19994.937947]
[19994.937947] -> #1 (&type->s_lock_key){+.+...}:
[19994.937950] [<ffffffff81061bff>] lock_acquire+0xd2/0xfe
[19994.937953] [<ffffffff81528ebf>] __mutex_lock_common+0x48/0x34d
[19994.937957] [<ffffffff81529273>] mutex_lock_nested+0x37/0x3c
[19994.937960] [<ffffffff810e6c70>] lock_super+0x22/0x24
[19994.937964] [<ffffffff81169f06>] ext4_remount+0x50/0x469
[19994.937967] [<ffffffff810e6f43>] do_remount_sb+0xfb/0x158
[19994.937969] [<ffffffff810fd36b>] do_mount+0x283/0x7e3
[19994.937972] [<ffffffff810fd94a>] sys_mount+0x7f/0xb9
[19994.937975] [<ffffffff810029c2>] system_call_fastpath+0x16/0x1b
[19994.937978]
[19994.937978] -> #0 (&type->s_umount_key#19){++++..}:
[19994.937982] [<ffffffff81061807>] __lock_acquire+0xaf9/0xe1f
[19994.937985] [<ffffffff81061bff>] lock_acquire+0xd2/0xfe
[19994.937987] [<ffffffff8152954d>] down_read+0x47/0x5a
[19994.937990] [<ffffffff810e729e>] iterate_supers+0x5d/0xb2
[19994.937993] [<ffffffff811052a4>] do_sync_work+0x28/0x5b
[19994.937995] [<ffffffff8104b627>] worker_thread+0x22c/0x332
[19994.937998] [<ffffffff8104f0ee>] kthread+0x7d/0x85
[19994.938001] [<ffffffff81003844>] kernel_thread_helper+0x4/0x10
[19994.938004]
[19994.938005] other info that might help us debug this:
[19994.938005]
[19994.938005] 2 locks held by events/0/7:
[19994.938005] #0: (events){+.+.+.}, at: [<ffffffff8104b5d0>] worker_thread+0x1d5/0x332
[19994.938005] #1: ((work)#3){+.+...}, at: [<ffffffff8104b5d0>] worker_thread+0x1d5/0x332
[19994.938005]
[19994.938005] stack backtrace:
[19994.938005] Pid: 7, comm: events/0 Not tainted 2.6.34-07097-gf4b87de-dirty #32
[19994.938005] Call Trace:
[19994.938005] [<ffffffff810608da>] print_circular_bug+0xc0/0xd1
[19994.938005] [<ffffffff81061807>] __lock_acquire+0xaf9/0xe1f
[19994.938005] [<ffffffff8152a9d0>] ? restore_args+0x0/0x30
[19994.938005] [<ffffffff81529dd4>] ? trace_hardirqs_on_thunk+0x3a/0x3f
[19994.938005] [<ffffffff81090418>] ? handle_edge_irq+0x101/0x12d
[19994.938005] [<ffffffff81061bff>] lock_acquire+0xd2/0xfe
[19994.938005] [<ffffffff810e729e>] ? iterate_supers+0x5d/0xb2
[19994.938005] [<ffffffff81105355>] ? sync_one_sb+0x0/0x1d
[19994.938005] [<ffffffff8152954d>] down_read+0x47/0x5a
[19994.938005] [<ffffffff810e729e>] ? iterate_supers+0x5d/0xb2
[19994.938005] [<ffffffff810e729e>] iterate_supers+0x5d/0xb2
[19994.938005] [<ffffffff811052a4>] do_sync_work+0x28/0x5b
[19994.938005] [<ffffffff8104b627>] worker_thread+0x22c/0x332
[19994.938005] [<ffffffff8104b5d0>] ? worker_thread+0x1d5/0x332
[19994.938005] [<ffffffff8102f911>] ? finish_task_switch+0x69/0xd9
[19994.938005] [<ffffffff8102f8a8>] ? finish_task_switch+0x0/0xd9
[19994.938005] [<ffffffff8110527c>] ? do_sync_work+0x0/0x5b
[19994.938005] [<ffffffff8104f54e>] ? autoremove_wake_function+0x0/0x38
[19994.938005] [<ffffffff8104b3fb>] ? worker_thread+0x0/0x332
[19994.938005] [<ffffffff8104f0ee>] kthread+0x7d/0x85
[19994.938005] [<ffffffff81003844>] kernel_thread_helper+0x4/0x10
[19994.938005] [<ffffffff8152a9d0>] ? restore_args+0x0/0x30
[19994.938005] [<ffffffff8104f071>] ? kthread+0x0/0x85
[19994.938005] [<ffffffff81003840>] ? kernel_thread_helper+0x0/0x10
[19994.938731] Emergency Sync complete
[19994.938768] Emergency Sync complete
--
Thanks
Yang Ruirui
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