Linus GIT (3.3.0-rc6+) -- INFO: possible circular locking dependency detected

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* Linus GIT (3.3.0-rc6+) -- INFO: possible circular locking dependency detected
@ 2012-03-05 21:08 Miles Lane
  2012-03-05 21:23 ` Andrew Morton
                   ` (2 more replies)
  0 siblings, 3 replies; 7+ messages in thread
From: Miles Lane @ 2012-03-05 21:08 UTC (permalink / raw)
  To: LKML, Theodore Ts'o, Andreas Dilger, Alexander Viro,
	Andrew Morton

[  107.839605] [ INFO: possible circular locking dependency detected ]
[  107.839608] 3.3.0-rc6+ #14 Not tainted
[  107.839609] -------------------------------------------------------
[  107.839611] gvfsd-metadata/2314 is trying to acquire lock:
[  107.839612]  (&sb->s_type->i_mutex_key#13){+.+.+.}, at:
[<ffffffff810ae65a>] generic_file_aio_write+0x45/0xbc
[  107.839622]
[  107.839623] but task is already holding lock:
[  107.839624]  (&mm->mmap_sem){++++++}, at: [<ffffffff810ca534>]
sys_munmap+0x36/0x5b
[  107.839630]
[  107.839630] which lock already depends on the new lock.
[  107.839631]
[  107.839632]
[  107.839632] the existing dependency chain (in reverse order) is:
[  107.839634]
[  107.839634] -> #1 (&mm->mmap_sem){++++++}:
[  107.839638]        [<ffffffff8107402d>] lock_acquire+0x8a/0xa7
[  107.839642]        [<ffffffff810c3363>] might_fault+0x7b/0x9e
[  107.839646]        [<ffffffff810f5246>] filldir+0x6a/0xc2
[  107.839649]        [<ffffffff81143b91>] call_filldir+0x91/0xb8
[  107.839653]        [<ffffffff81143eb2>] ext4_readdir+0x1b2/0x519
[  107.839656]        [<ffffffff810f548c>] vfs_readdir+0x76/0xac
[  107.839658]        [<ffffffff810f559e>] sys_getdents+0x79/0xc9
[  107.839661]        [<ffffffff813a1fb9>] system_call_fastpath+0x16/0x1b
[  107.839665]
[  107.839665] -> #0 (&sb->s_type->i_mutex_key#13){+.+.+.}:
[  107.839669]        [<ffffffff81073918>] __lock_acquire+0xa81/0xd75
[  107.839672]        [<ffffffff8107402d>] lock_acquire+0x8a/0xa7
[  107.839675]        [<ffffffff8139acfe>] __mutex_lock_common+0x61/0x456
[  107.839679]        [<ffffffff8139b1da>] mutex_lock_nested+0x36/0x3b
[  107.839681]        [<ffffffff810ae65a>] generic_file_aio_write+0x45/0xbc
[  107.839684]        [<ffffffff8114478e>] ext4_file_write+0x1e2/0x23a
[  107.839687]        [<ffffffff810e5bb5>] do_sync_write+0xbd/0xfd
[  107.839691]        [<ffffffff810e6333>] vfs_write+0xa7/0xee
[  107.839694]        [<ffffffffa037f266>]
ecryptfs_write_lower+0x4e/0x73 [ecryptfs]
[  107.839700]        [<ffffffffa03803d3>]
ecryptfs_encrypt_page+0x11c/0x182 [ecryptfs]
[  107.839704]        [<ffffffffa037e967>]
ecryptfs_writepage+0x31/0x73 [ecryptfs]
[  107.839708]        [<ffffffff810b448b>] __writepage+0x12/0x31
[  107.839710]        [<ffffffff810b4b25>] write_cache_pages+0x1e6/0x310
[  107.839713]        [<ffffffff810b4c8d>] generic_writepages+0x3e/0x54
[  107.839716]        [<ffffffff810b5e05>] do_writepages+0x26/0x28
[  107.839719]        [<ffffffff810ae1e4>] __filemap_fdatawrite_range+0x4e/0x50
[  107.839722]        [<ffffffff810aed55>] filemap_fdatawrite+0x1a/0x1c
[  107.839725]        [<ffffffff810aed72>] filemap_write_and_wait+0x1b/0x36
[  107.839727]        [<ffffffffa037c1bb>]
ecryptfs_vma_close+0x17/0x19 [ecryptfs]
[  107.839731]        [<ffffffff810c9374>] remove_vma+0x3b/0x71
[  107.839733]        [<ffffffff810ca40c>] do_munmap+0x2ed/0x306
[  107.839735]        [<ffffffff810ca542>] sys_munmap+0x44/0x5b
[  107.839738]        [<ffffffff813a1fb9>] system_call_fastpath+0x16/0x1b
[  107.839741]
[  107.839741] other info that might help us debug this:
[  107.839741]
[  107.839743]  Possible unsafe locking scenario:
[  107.839743]
[  107.839744]        CPU0                    CPU1
[  107.839746]        ----                    ----
[  107.839747]   lock(&mm->mmap_sem);
[  107.839749]                                lock(&sb->s_type->i_mutex_key#13);
[  107.839753]                                lock(&mm->mmap_sem);
[  107.839755]   lock(&sb->s_type->i_mutex_key#13);
[  107.839758]
[  107.839758]  *** DEADLOCK ***
[  107.839759]
[  107.839761] 1 lock held by gvfsd-metadata/2314:
[  107.839762]  #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff810ca534>]
sys_munmap+0x36/0x5b
[  107.839767]
[  107.839767] stack backtrace:
[  107.839769] Pid: 2314, comm: gvfsd-metadata Not tainted 3.3.0-rc6+ #14
[  107.839771] Call Trace:
[  107.839775]  [<ffffffff813956a2>] print_circular_bug+0x1f8/0x209
[  107.839778]  [<ffffffff81073918>] __lock_acquire+0xa81/0xd75
[  107.839781]  [<ffffffff81073bfd>] ? __lock_acquire+0xd66/0xd75
[  107.839784]  [<ffffffff8107402d>] lock_acquire+0x8a/0xa7
[  107.839787]  [<ffffffff810ae65a>] ? generic_file_aio_write+0x45/0xbc
[  107.839790]  [<ffffffff8139acfe>] __mutex_lock_common+0x61/0x456
[  107.839792]  [<ffffffff810ae65a>] ? generic_file_aio_write+0x45/0xbc
[  107.839795]  [<ffffffff81071a96>] ? mark_lock+0x2d/0x258
[  107.839798]  [<ffffffff810ae65a>] ? generic_file_aio_write+0x45/0xbc
[  107.839801]  [<ffffffff8107299e>] ? lock_is_held+0x92/0x9d
[  107.839803]  [<ffffffff8139b1da>] mutex_lock_nested+0x36/0x3b
[  107.839806]  [<ffffffff810ae65a>] generic_file_aio_write+0x45/0xbc
[  107.839810]  [<ffffffff811a013f>] ? scatterwalk_map+0x2b/0x5d
[  107.839813]  [<ffffffff810570d4>] ? get_parent_ip+0xe/0x3e
[  107.839816]  [<ffffffff8114478e>] ext4_file_write+0x1e2/0x23a
[  107.839818]  [<ffffffff81071a96>] ? mark_lock+0x2d/0x258
[  107.839821]  [<ffffffff810e5bb5>] do_sync_write+0xbd/0xfd
[  107.839824]  [<ffffffff8139b2fd>] ? __mutex_unlock_slowpath+0x11e/0x152
[  107.839828]  [<ffffffff81197092>] ? security_file_permission+0x29/0x2e
[  107.839831]  [<ffffffff810e60b2>] ? rw_verify_area+0xab/0xc8
[  107.839834]  [<ffffffff810e6333>] vfs_write+0xa7/0xee
[  107.839838]  [<ffffffffa037f266>] ecryptfs_write_lower+0x4e/0x73 [ecryptfs]
[  107.839842]  [<ffffffffa03803d3>] ecryptfs_encrypt_page+0x11c/0x182
[ecryptfs]
[  107.839846]  [<ffffffffa037e967>] ecryptfs_writepage+0x31/0x73 [ecryptfs]
[  107.839849]  [<ffffffff810b448b>] __writepage+0x12/0x31
[  107.839851]  [<ffffffff810b4b25>] write_cache_pages+0x1e6/0x310
[  107.839854]  [<ffffffff810b4479>] ? bdi_set_max_ratio+0x6a/0x6a
[  107.839857]  [<ffffffff813a03c1>] ? sub_preempt_count+0x90/0xa3
[  107.839860]  [<ffffffff810b4c8d>] generic_writepages+0x3e/0x54
[  107.839863]  [<ffffffff810b5e05>] do_writepages+0x26/0x28
[  107.839866]  [<ffffffff810ae1e4>] __filemap_fdatawrite_range+0x4e/0x50
[  107.839869]  [<ffffffff810aed55>] filemap_fdatawrite+0x1a/0x1c
[  107.839871]  [<ffffffff810aed72>] filemap_write_and_wait+0x1b/0x36
[  107.839875]  [<ffffffffa037c1bb>] ecryptfs_vma_close+0x17/0x19 [ecryptfs]
[  107.839877]  [<ffffffff810c9374>] remove_vma+0x3b/0x71
[  107.839879]  [<ffffffff810ca40c>] do_munmap+0x2ed/0x306
[  107.839882]  [<ffffffff810ca542>] sys_munmap+0x44/0x5b
[  107.839884]  [<ffffffff813a1fb9>] system_call_fastpath+0x16/0x1b

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: Linus GIT (3.3.0-rc6+) -- INFO: possible circular locking dependency detected
  2012-03-05 21:08 Linus GIT (3.3.0-rc6+) -- INFO: possible circular locking dependency detected Miles Lane
@ 2012-03-05 21:23 ` Andrew Morton
  2012-03-05 21:35   ` Al Viro
  2012-03-05 21:33 ` Al Viro
  2012-03-05 21:46 ` Ted Ts'o
  2 siblings, 1 reply; 7+ messages in thread
From: Andrew Morton @ 2012-03-05 21:23 UTC (permalink / raw)
  To: Miles Lane
  Cc: LKML, Theodore Ts'o, Andreas Dilger, Alexander Viro,
	Tyler Hicks, Dustin Kirkland, ecryptfs

On Mon, 5 Mar 2012 16:08:55 -0500
Miles Lane <miles.lane@gmail.com> wrote:

> [  107.839605] [ INFO: possible circular locking dependency detected ]
> [  107.839608] 3.3.0-rc6+ #14 Not tainted
> [  107.839609] -------------------------------------------------------
> [  107.839611] gvfsd-metadata/2314 is trying to acquire lock:
> [  107.839612]  (&sb->s_type->i_mutex_key#13){+.+.+.}, at:
> [<ffffffff810ae65a>] generic_file_aio_write+0x45/0xbc
> [  107.839622]
> [  107.839623] but task is already holding lock:
> [  107.839624]  (&mm->mmap_sem){++++++}, at: [<ffffffff810ca534>]
> sys_munmap+0x36/0x5b
> [  107.839630]
> [  107.839630] which lock already depends on the new lock.
> [  107.839631]
> [  107.839632]
> [  107.839632] the existing dependency chain (in reverse order) is:
> [  107.839634]
> [  107.839634] -> #1 (&mm->mmap_sem){++++++}:
> [  107.839638]        [<ffffffff8107402d>] lock_acquire+0x8a/0xa7
> [  107.839642]        [<ffffffff810c3363>] might_fault+0x7b/0x9e
> [  107.839646]        [<ffffffff810f5246>] filldir+0x6a/0xc2
> [  107.839649]        [<ffffffff81143b91>] call_filldir+0x91/0xb8
> [  107.839653]        [<ffffffff81143eb2>] ext4_readdir+0x1b2/0x519
> [  107.839656]        [<ffffffff810f548c>] vfs_readdir+0x76/0xac
> [  107.839658]        [<ffffffff810f559e>] sys_getdents+0x79/0xc9
> [  107.839661]        [<ffffffff813a1fb9>] system_call_fastpath+0x16/0x1b
> [  107.839665]
> [  107.839665] -> #0 (&sb->s_type->i_mutex_key#13){+.+.+.}:
> [  107.839669]        [<ffffffff81073918>] __lock_acquire+0xa81/0xd75
> [  107.839672]        [<ffffffff8107402d>] lock_acquire+0x8a/0xa7
> [  107.839675]        [<ffffffff8139acfe>] __mutex_lock_common+0x61/0x456
> [  107.839679]        [<ffffffff8139b1da>] mutex_lock_nested+0x36/0x3b
> [  107.839681]        [<ffffffff810ae65a>] generic_file_aio_write+0x45/0xbc
> [  107.839684]        [<ffffffff8114478e>] ext4_file_write+0x1e2/0x23a
> [  107.839687]        [<ffffffff810e5bb5>] do_sync_write+0xbd/0xfd
> [  107.839691]        [<ffffffff810e6333>] vfs_write+0xa7/0xee
> [  107.839694]        [<ffffffffa037f266>]
> ecryptfs_write_lower+0x4e/0x73 [ecryptfs]
> [  107.839700]        [<ffffffffa03803d3>]
> ecryptfs_encrypt_page+0x11c/0x182 [ecryptfs]
> [  107.839704]        [<ffffffffa037e967>]
> ecryptfs_writepage+0x31/0x73 [ecryptfs]
> [  107.839708]        [<ffffffff810b448b>] __writepage+0x12/0x31
> [  107.839710]        [<ffffffff810b4b25>] write_cache_pages+0x1e6/0x310
> [  107.839713]        [<ffffffff810b4c8d>] generic_writepages+0x3e/0x54
> [  107.839716]        [<ffffffff810b5e05>] do_writepages+0x26/0x28
> [  107.839719]        [<ffffffff810ae1e4>] __filemap_fdatawrite_range+0x4e/0x50
> [  107.839722]        [<ffffffff810aed55>] filemap_fdatawrite+0x1a/0x1c
> [  107.839725]        [<ffffffff810aed72>] filemap_write_and_wait+0x1b/0x36
> [  107.839727]        [<ffffffffa037c1bb>]
> ecryptfs_vma_close+0x17/0x19 [ecryptfs]
> [  107.839731]        [<ffffffff810c9374>] remove_vma+0x3b/0x71
> [  107.839733]        [<ffffffff810ca40c>] do_munmap+0x2ed/0x306
> [  107.839735]        [<ffffffff810ca542>] sys_munmap+0x44/0x5b
> [  107.839738]        [<ffffffff813a1fb9>] system_call_fastpath+0x16/0x1b
> [  107.839741]
> [  107.839741] other info that might help us debug this:
> [  107.839741]
> [  107.839743]  Possible unsafe locking scenario:
> [  107.839743]
> [  107.839744]        CPU0                    CPU1
> [  107.839746]        ----                    ----
> [  107.839747]   lock(&mm->mmap_sem);
> [  107.839749]                                lock(&sb->s_type->i_mutex_key#13);
> [  107.839753]                                lock(&mm->mmap_sem);
> [  107.839755]   lock(&sb->s_type->i_mutex_key#13);
> [  107.839758]
> [  107.839758]  *** DEADLOCK ***
> [  107.839759]
> [  107.839761] 1 lock held by gvfsd-metadata/2314:
> [  107.839762]  #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff810ca534>]
> sys_munmap+0x36/0x5b
> [  107.839767]
> [  107.839767] stack backtrace:
> [  107.839769] Pid: 2314, comm: gvfsd-metadata Not tainted 3.3.0-rc6+ #14
> [  107.839771] Call Trace:
> [  107.839775]  [<ffffffff813956a2>] print_circular_bug+0x1f8/0x209
> [  107.839778]  [<ffffffff81073918>] __lock_acquire+0xa81/0xd75
> [  107.839781]  [<ffffffff81073bfd>] ? __lock_acquire+0xd66/0xd75
> [  107.839784]  [<ffffffff8107402d>] lock_acquire+0x8a/0xa7
> [  107.839787]  [<ffffffff810ae65a>] ? generic_file_aio_write+0x45/0xbc
> [  107.839790]  [<ffffffff8139acfe>] __mutex_lock_common+0x61/0x456
> [  107.839792]  [<ffffffff810ae65a>] ? generic_file_aio_write+0x45/0xbc
> [  107.839795]  [<ffffffff81071a96>] ? mark_lock+0x2d/0x258
> [  107.839798]  [<ffffffff810ae65a>] ? generic_file_aio_write+0x45/0xbc
> [  107.839801]  [<ffffffff8107299e>] ? lock_is_held+0x92/0x9d
> [  107.839803]  [<ffffffff8139b1da>] mutex_lock_nested+0x36/0x3b
> [  107.839806]  [<ffffffff810ae65a>] generic_file_aio_write+0x45/0xbc
> [  107.839810]  [<ffffffff811a013f>] ? scatterwalk_map+0x2b/0x5d
> [  107.839813]  [<ffffffff810570d4>] ? get_parent_ip+0xe/0x3e
> [  107.839816]  [<ffffffff8114478e>] ext4_file_write+0x1e2/0x23a
> [  107.839818]  [<ffffffff81071a96>] ? mark_lock+0x2d/0x258
> [  107.839821]  [<ffffffff810e5bb5>] do_sync_write+0xbd/0xfd
> [  107.839824]  [<ffffffff8139b2fd>] ? __mutex_unlock_slowpath+0x11e/0x152
> [  107.839828]  [<ffffffff81197092>] ? security_file_permission+0x29/0x2e
> [  107.839831]  [<ffffffff810e60b2>] ? rw_verify_area+0xab/0xc8
> [  107.839834]  [<ffffffff810e6333>] vfs_write+0xa7/0xee
> [  107.839838]  [<ffffffffa037f266>] ecryptfs_write_lower+0x4e/0x73 [ecryptfs]
> [  107.839842]  [<ffffffffa03803d3>] ecryptfs_encrypt_page+0x11c/0x182
> [ecryptfs]
> [  107.839846]  [<ffffffffa037e967>] ecryptfs_writepage+0x31/0x73 [ecryptfs]
> [  107.839849]  [<ffffffff810b448b>] __writepage+0x12/0x31
> [  107.839851]  [<ffffffff810b4b25>] write_cache_pages+0x1e6/0x310
> [  107.839854]  [<ffffffff810b4479>] ? bdi_set_max_ratio+0x6a/0x6a
> [  107.839857]  [<ffffffff813a03c1>] ? sub_preempt_count+0x90/0xa3
> [  107.839860]  [<ffffffff810b4c8d>] generic_writepages+0x3e/0x54
> [  107.839863]  [<ffffffff810b5e05>] do_writepages+0x26/0x28
> [  107.839866]  [<ffffffff810ae1e4>] __filemap_fdatawrite_range+0x4e/0x50
> [  107.839869]  [<ffffffff810aed55>] filemap_fdatawrite+0x1a/0x1c
> [  107.839871]  [<ffffffff810aed72>] filemap_write_and_wait+0x1b/0x36
> [  107.839875]  [<ffffffffa037c1bb>] ecryptfs_vma_close+0x17/0x19 [ecryptfs]
> [  107.839877]  [<ffffffff810c9374>] remove_vma+0x3b/0x71
> [  107.839879]  [<ffffffff810ca40c>] do_munmap+0x2ed/0x306
> [  107.839882]  [<ffffffff810ca542>] sys_munmap+0x44/0x5b
> [  107.839884]  [<ffffffff813a1fb9>] system_call_fastpath+0x16/0x1b

mmap_sem nests inside i_mutex.

On the path

	munmap
	->ecryptfs_vma_close
	  ->filemap_write_and_wait
	    ->generic_file_aio_write

we're taking i_mutex inside mmap_sem.  So the problem is triggered by
ecryptfs_vma_close() calling filemap_write_and_wait() inside munmap()'s
mmap_sem.

Question is: what did we recently change to cause this to happen?

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: Linus GIT (3.3.0-rc6+) -- INFO: possible circular locking dependency detected
  2012-03-05 21:23 ` Andrew Morton
@ 2012-03-05 21:35   ` Al Viro
  2012-03-05 21:46     ` Tyler Hicks
  0 siblings, 1 reply; 7+ messages in thread
From: Al Viro @ 2012-03-05 21:35 UTC (permalink / raw)
  To: Andrew Morton
  Cc: Miles Lane, LKML, Theodore Ts'o, Andreas Dilger, Tyler Hicks,
	Dustin Kirkland, ecryptfs

On Mon, Mar 05, 2012 at 01:23:34PM -0800, Andrew Morton wrote:
> mmap_sem nests inside i_mutex.
> 
> On the path
> 
> 	munmap
> 	->ecryptfs_vma_close
> 	  ->filemap_write_and_wait
> 	    ->generic_file_aio_write
> 
> we're taking i_mutex inside mmap_sem.  So the problem is triggered by
> ecryptfs_vma_close() calling filemap_write_and_wait() inside munmap()'s
> mmap_sem.
> 
> Question is: what did we recently change to cause this to happen?

AFAICS, it's commit 32001d6fe9ac6b0423e674a3093aa56740849f3b
Author: Tyler Hicks <tyhicks@canonical.com>
Date:   Mon Nov 21 17:31:29 2011 -0600

    eCryptfs: Flush file in vma close

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: Linus GIT (3.3.0-rc6+) -- INFO: possible circular locking dependency detected
  2012-03-05 21:35   ` Al Viro
@ 2012-03-05 21:46     ` Tyler Hicks
  0 siblings, 0 replies; 7+ messages in thread
From: Tyler Hicks @ 2012-03-05 21:46 UTC (permalink / raw)
  To: Al Viro
  Cc: Andrew Morton, Miles Lane, LKML, Theodore Ts'o,
	Andreas Dilger, Dustin Kirkland, ecryptfs

[-- Attachment #1: Type: text/plain, Size: 1399 bytes --]

On 2012-03-05 21:35:58, Al Viro wrote:
> On Mon, Mar 05, 2012 at 01:23:34PM -0800, Andrew Morton wrote:
> > mmap_sem nests inside i_mutex.
> > 
> > On the path
> > 
> > 	munmap
> > 	->ecryptfs_vma_close
> > 	  ->filemap_write_and_wait
> > 	    ->generic_file_aio_write
> > 
> > we're taking i_mutex inside mmap_sem.  So the problem is triggered by
> > ecryptfs_vma_close() calling filemap_write_and_wait() inside munmap()'s
> > mmap_sem.
> > 
> > Question is: what did we recently change to cause this to happen?
> 
> AFAICS, it's commit 32001d6fe9ac6b0423e674a3093aa56740849f3b
> Author: Tyler Hicks <tyhicks@canonical.com>
> Date:   Mon Nov 21 17:31:29 2011 -0600
> 
>     eCryptfs: Flush file in vma close

Yes, it is definitely this commit. This is mainly what brought about my
patch to fix the incorrect logic around lockdep_set_class() in
lockdep_annotate_inode_mutex_key(). With that patch, I no longer saw
these lockdep warnings, so I wrote it off. Al has since made it clear
that this locking order is wrong.

This should fix itself when I revert
57db4e8d73ef2b5e94a3f412108dff2576670a8a. We'll no longer need this
flush in vma_close(), so 32001d6fe9ac6b0423e674a3093aa56740849f3b will
be reverted, too. I was planning on waiting until 3.4 to do all of that
since it will be a somewhat big change (even though it is mainly
reverting of patches).

Tyler

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^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: Linus GIT (3.3.0-rc6+) -- INFO: possible circular locking dependency detected
  2012-03-05 21:08 Linus GIT (3.3.0-rc6+) -- INFO: possible circular locking dependency detected Miles Lane
  2012-03-05 21:23 ` Andrew Morton
@ 2012-03-05 21:33 ` Al Viro
  2012-03-05 21:46 ` Ted Ts'o
  2 siblings, 0 replies; 7+ messages in thread
From: Al Viro @ 2012-03-05 21:33 UTC (permalink / raw)
  To: Miles Lane; +Cc: LKML, Theodore Ts'o, Andreas Dilger, Andrew Morton

On Mon, Mar 05, 2012 at 04:08:55PM -0500, Miles Lane wrote:

> [  107.839634] -> #1 (&mm->mmap_sem){++++++}:
[readdir() grabs ->mmap_sem under ->i_mutex - true, but irrelevant; more
to the point, write() on just about anything will grab ->mmap_sem under
->i_mutex, and that one happens for non-directories]

> [  107.839665] -> #0 (&sb->s_type->i_mutex_key#13){+.+.+.}:
[generic_file_aio_write() grabs ->i_mutex after being called from
vfs_write(), called from...]
> [  107.839691]        [<ffffffff810e6333>] vfs_write+0xa7/0xee
> [  107.839694]        [<ffffffffa037f266>]
> ecryptfs_write_lower+0x4e/0x73 [ecryptfs]
> [  107.839700]        [<ffffffffa03803d3>]
> ecryptfs_encrypt_page+0x11c/0x182 [ecryptfs]
> [  107.839704]        [<ffffffffa037e967>]
> ecryptfs_writepage+0x31/0x73 [ecryptfs]
> [  107.839708]        [<ffffffff810b448b>] __writepage+0x12/0x31
> [  107.839710]        [<ffffffff810b4b25>] write_cache_pages+0x1e6/0x310
> [  107.839713]        [<ffffffff810b4c8d>] generic_writepages+0x3e/0x54
> [  107.839716]        [<ffffffff810b5e05>] do_writepages+0x26/0x28
> [  107.839719]        [<ffffffff810ae1e4>] __filemap_fdatawrite_range+0x4e/0x50
> [  107.839722]        [<ffffffff810aed55>] filemap_fdatawrite+0x1a/0x1c
> [  107.839725]        [<ffffffff810aed72>] filemap_write_and_wait+0x1b/0x36
> [  107.839727]        [<ffffffffa037c1bb>]
> ecryptfs_vma_close+0x17/0x19 [ecryptfs]

Bloody wonderful...  That would do it, all right.  Forget about readdir(),
the deadlock is real and has nothing to do with directories.  Ecryptfs bug,
AFAICS.

Thread A:
	mmap something on ecryptfs, dirty it.
Thread B: open underlying file for write, 
	later
Thread A: munmap() | Thread B: write() (from unrelated buffer)

A holds ->mmap_sem, B holds ->i_mutex.
A is blocked essentially on attempt to do what B is doing (write to underlying
file; any mutex whatever_fs_write() might be holding around copy_from_user()
will do for that deadlock).
B is blocked trying to fault some pages in.

Fun...

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: Linus GIT (3.3.0-rc6+) -- INFO: possible circular locking dependency detected
  2012-03-05 21:08 Linus GIT (3.3.0-rc6+) -- INFO: possible circular locking dependency detected Miles Lane
  2012-03-05 21:23 ` Andrew Morton
  2012-03-05 21:33 ` Al Viro
@ 2012-03-05 21:46 ` Ted Ts'o
  2012-03-05 22:02   ` Ted Ts'o
  2 siblings, 1 reply; 7+ messages in thread
From: Ted Ts'o @ 2012-03-05 21:46 UTC (permalink / raw)
  To: Miles Lane; +Cc: LKML, Andreas Dilger, Alexander Viro, Andrew Morton, ecryptfs

I've added ecryptfs to the list since this looks like it's caused by
ecryptfs (i.e., it won't happen without ecryptfs).

This seems to be caused by an munmap of an ecryptfs file, which has
dirty pages; ecryptfs is then calling into ext4 while the mmap is
still holding the mmap_sem, and then when ext4 calls the generic
function generic_file_aio_write(), it tries to grab the inode's
i_mutex, and that's what's causing the possible circular locking
dependency.

The other locking order is caused by vfs_readdir() grabbing i_mutex,
and then filldir() calling writing to user memory, which means it
calls might_fault(), and might_fault() calls
might_lock_read(&current->mm->mmap_sem) since if the page needs to be
faulted in, *that* will require taking a read lock of mmap_sem.

In any case, all of the locks in question are being taken by generic
code, and it's the fact that ecryptfs needs to try to initiate page
writeout at munmap() time, which holds mmap_sem, which is causing the
circular dependency.

i.e., this particular problem can and will happen with any file system
(which uses generic filemap infrastructure); ext4 just happens to
appear in the stack trace because that's the underlying file system
used by ecryptfs.

Regards,

					- Ted

On Mon, Mar 05, 2012 at 04:08:55PM -0500, Miles Lane wrote:
> [  107.839605] [ INFO: possible circular locking dependency detected ]
> [  107.839608] 3.3.0-rc6+ #14 Not tainted
> [  107.839609] -------------------------------------------------------
> [  107.839611] gvfsd-metadata/2314 is trying to acquire lock:
> [  107.839612]  (&sb->s_type->i_mutex_key#13){+.+.+.}, at:
> [<ffffffff810ae65a>] generic_file_aio_write+0x45/0xbc
> [  107.839622]
> [  107.839623] but task is already holding lock:
> [  107.839624]  (&mm->mmap_sem){++++++}, at: [<ffffffff810ca534>]
> sys_munmap+0x36/0x5b
> [  107.839630]
> [  107.839630] which lock already depends on the new lock.
> [  107.839631]
> [  107.839632]
> [  107.839632] the existing dependency chain (in reverse order) is:
> [  107.839634]
> [  107.839634] -> #1 (&mm->mmap_sem){++++++}:
> [  107.839638]        [<ffffffff8107402d>] lock_acquire+0x8a/0xa7
> [  107.839642]        [<ffffffff810c3363>] might_fault+0x7b/0x9e
> [  107.839646]        [<ffffffff810f5246>] filldir+0x6a/0xc2
> [  107.839649]        [<ffffffff81143b91>] call_filldir+0x91/0xb8
> [  107.839653]        [<ffffffff81143eb2>] ext4_readdir+0x1b2/0x519
> [  107.839656]        [<ffffffff810f548c>] vfs_readdir+0x76/0xac
> [  107.839658]        [<ffffffff810f559e>] sys_getdents+0x79/0xc9
> [  107.839661]        [<ffffffff813a1fb9>] system_call_fastpath+0x16/0x1b
> [  107.839665]
> [  107.839665] -> #0 (&sb->s_type->i_mutex_key#13){+.+.+.}:
> [  107.839669]        [<ffffffff81073918>] __lock_acquire+0xa81/0xd75
> [  107.839672]        [<ffffffff8107402d>] lock_acquire+0x8a/0xa7
> [  107.839675]        [<ffffffff8139acfe>] __mutex_lock_common+0x61/0x456
> [  107.839679]        [<ffffffff8139b1da>] mutex_lock_nested+0x36/0x3b
> [  107.839681]        [<ffffffff810ae65a>] generic_file_aio_write+0x45/0xbc
> [  107.839684]        [<ffffffff8114478e>] ext4_file_write+0x1e2/0x23a
> [  107.839687]        [<ffffffff810e5bb5>] do_sync_write+0xbd/0xfd
> [  107.839691]        [<ffffffff810e6333>] vfs_write+0xa7/0xee
> [  107.839694]        [<ffffffffa037f266>]
> ecryptfs_write_lower+0x4e/0x73 [ecryptfs]
> [  107.839700]        [<ffffffffa03803d3>]
> ecryptfs_encrypt_page+0x11c/0x182 [ecryptfs]
> [  107.839704]        [<ffffffffa037e967>]
> ecryptfs_writepage+0x31/0x73 [ecryptfs]
> [  107.839708]        [<ffffffff810b448b>] __writepage+0x12/0x31
> [  107.839710]        [<ffffffff810b4b25>] write_cache_pages+0x1e6/0x310
> [  107.839713]        [<ffffffff810b4c8d>] generic_writepages+0x3e/0x54
> [  107.839716]        [<ffffffff810b5e05>] do_writepages+0x26/0x28
> [  107.839719]        [<ffffffff810ae1e4>] __filemap_fdatawrite_range+0x4e/0x50
> [  107.839722]        [<ffffffff810aed55>] filemap_fdatawrite+0x1a/0x1c
> [  107.839725]        [<ffffffff810aed72>] filemap_write_and_wait+0x1b/0x36
> [  107.839727]        [<ffffffffa037c1bb>]
> ecryptfs_vma_close+0x17/0x19 [ecryptfs]
> [  107.839731]        [<ffffffff810c9374>] remove_vma+0x3b/0x71
> [  107.839733]        [<ffffffff810ca40c>] do_munmap+0x2ed/0x306
> [  107.839735]        [<ffffffff810ca542>] sys_munmap+0x44/0x5b
> [  107.839738]        [<ffffffff813a1fb9>] system_call_fastpath+0x16/0x1b
> [  107.839741]
> [  107.839741] other info that might help us debug this:
> [  107.839741]
> [  107.839743]  Possible unsafe locking scenario:
> [  107.839743]
> [  107.839744]        CPU0                    CPU1
> [  107.839746]        ----                    ----
> [  107.839747]   lock(&mm->mmap_sem);
> [  107.839749]                                lock(&sb->s_type->i_mutex_key#13);
> [  107.839753]                                lock(&mm->mmap_sem);
> [  107.839755]   lock(&sb->s_type->i_mutex_key#13);
> [  107.839758]
> [  107.839758]  *** DEADLOCK ***
> [  107.839759]
> [  107.839761] 1 lock held by gvfsd-metadata/2314:
> [  107.839762]  #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff810ca534>]
> sys_munmap+0x36/0x5b
> [  107.839767]
> [  107.839767] stack backtrace:
> [  107.839769] Pid: 2314, comm: gvfsd-metadata Not tainted 3.3.0-rc6+ #14
> [  107.839771] Call Trace:
> [  107.839775]  [<ffffffff813956a2>] print_circular_bug+0x1f8/0x209
> [  107.839778]  [<ffffffff81073918>] __lock_acquire+0xa81/0xd75
> [  107.839781]  [<ffffffff81073bfd>] ? __lock_acquire+0xd66/0xd75
> [  107.839784]  [<ffffffff8107402d>] lock_acquire+0x8a/0xa7
> [  107.839787]  [<ffffffff810ae65a>] ? generic_file_aio_write+0x45/0xbc
> [  107.839790]  [<ffffffff8139acfe>] __mutex_lock_common+0x61/0x456
> [  107.839792]  [<ffffffff810ae65a>] ? generic_file_aio_write+0x45/0xbc
> [  107.839795]  [<ffffffff81071a96>] ? mark_lock+0x2d/0x258
> [  107.839798]  [<ffffffff810ae65a>] ? generic_file_aio_write+0x45/0xbc
> [  107.839801]  [<ffffffff8107299e>] ? lock_is_held+0x92/0x9d
> [  107.839803]  [<ffffffff8139b1da>] mutex_lock_nested+0x36/0x3b
> [  107.839806]  [<ffffffff810ae65a>] generic_file_aio_write+0x45/0xbc
> [  107.839810]  [<ffffffff811a013f>] ? scatterwalk_map+0x2b/0x5d
> [  107.839813]  [<ffffffff810570d4>] ? get_parent_ip+0xe/0x3e
> [  107.839816]  [<ffffffff8114478e>] ext4_file_write+0x1e2/0x23a
> [  107.839818]  [<ffffffff81071a96>] ? mark_lock+0x2d/0x258
> [  107.839821]  [<ffffffff810e5bb5>] do_sync_write+0xbd/0xfd
> [  107.839824]  [<ffffffff8139b2fd>] ? __mutex_unlock_slowpath+0x11e/0x152
> [  107.839828]  [<ffffffff81197092>] ? security_file_permission+0x29/0x2e
> [  107.839831]  [<ffffffff810e60b2>] ? rw_verify_area+0xab/0xc8
> [  107.839834]  [<ffffffff810e6333>] vfs_write+0xa7/0xee
> [  107.839838]  [<ffffffffa037f266>] ecryptfs_write_lower+0x4e/0x73 [ecryptfs]
> [  107.839842]  [<ffffffffa03803d3>] ecryptfs_encrypt_page+0x11c/0x182
> [ecryptfs]
> [  107.839846]  [<ffffffffa037e967>] ecryptfs_writepage+0x31/0x73 [ecryptfs]
> [  107.839849]  [<ffffffff810b448b>] __writepage+0x12/0x31
> [  107.839851]  [<ffffffff810b4b25>] write_cache_pages+0x1e6/0x310
> [  107.839854]  [<ffffffff810b4479>] ? bdi_set_max_ratio+0x6a/0x6a
> [  107.839857]  [<ffffffff813a03c1>] ? sub_preempt_count+0x90/0xa3
> [  107.839860]  [<ffffffff810b4c8d>] generic_writepages+0x3e/0x54
> [  107.839863]  [<ffffffff810b5e05>] do_writepages+0x26/0x28
> [  107.839866]  [<ffffffff810ae1e4>] __filemap_fdatawrite_range+0x4e/0x50
> [  107.839869]  [<ffffffff810aed55>] filemap_fdatawrite+0x1a/0x1c
> [  107.839871]  [<ffffffff810aed72>] filemap_write_and_wait+0x1b/0x36
> [  107.839875]  [<ffffffffa037c1bb>] ecryptfs_vma_close+0x17/0x19 [ecryptfs]
> [  107.839877]  [<ffffffff810c9374>] remove_vma+0x3b/0x71
> [  107.839879]  [<ffffffff810ca40c>] do_munmap+0x2ed/0x306
> [  107.839882]  [<ffffffff810ca542>] sys_munmap+0x44/0x5b
> [  107.839884]  [<ffffffff813a1fb9>] system_call_fastpath+0x16/0x1b

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: Linus GIT (3.3.0-rc6+) -- INFO: possible circular locking dependency detected
  2012-03-05 21:46 ` Ted Ts'o
@ 2012-03-05 22:02   ` Ted Ts'o
  0 siblings, 0 replies; 7+ messages in thread
From: Ted Ts'o @ 2012-03-05 22:02 UTC (permalink / raw)
  To: Miles Lane, LKML, Andreas Dilger, Alexander Viro, Andrew Morton,
	ecryptfs

Ah, I see Al Viro has beaten me to the punch.  :-)

          	     	      	     - Ted

On Mon, Mar 05, 2012 at 04:46:28PM -0500, Ted Ts'o wrote:
> I've added ecryptfs to the list since this looks like it's caused by
> ecryptfs (i.e., it won't happen without ecryptfs).
> 
> This seems to be caused by an munmap of an ecryptfs file, which has
> dirty pages; ecryptfs is then calling into ext4 while the mmap is
> still holding the mmap_sem, and then when ext4 calls the generic
> function generic_file_aio_write(), it tries to grab the inode's
> i_mutex, and that's what's causing the possible circular locking
> dependency.
> 
> The other locking order is caused by vfs_readdir() grabbing i_mutex,
> and then filldir() calling writing to user memory, which means it
> calls might_fault(), and might_fault() calls
> might_lock_read(&current->mm->mmap_sem) since if the page needs to be
> faulted in, *that* will require taking a read lock of mmap_sem.
> 
> In any case, all of the locks in question are being taken by generic
> code, and it's the fact that ecryptfs needs to try to initiate page
> writeout at munmap() time, which holds mmap_sem, which is causing the
> circular dependency.
> 
> i.e., this particular problem can and will happen with any file system
> (which uses generic filemap infrastructure); ext4 just happens to
> appear in the stack trace because that's the underlying file system
> used by ecryptfs.
> 
> Regards,
> 
> 					- Ted
> 
> On Mon, Mar 05, 2012 at 04:08:55PM -0500, Miles Lane wrote:
> > [  107.839605] [ INFO: possible circular locking dependency detected ]
> > [  107.839608] 3.3.0-rc6+ #14 Not tainted
> > [  107.839609] -------------------------------------------------------
> > [  107.839611] gvfsd-metadata/2314 is trying to acquire lock:
> > [  107.839612]  (&sb->s_type->i_mutex_key#13){+.+.+.}, at:
> > [<ffffffff810ae65a>] generic_file_aio_write+0x45/0xbc
> > [  107.839622]
> > [  107.839623] but task is already holding lock:
> > [  107.839624]  (&mm->mmap_sem){++++++}, at: [<ffffffff810ca534>]
> > sys_munmap+0x36/0x5b
> > [  107.839630]
> > [  107.839630] which lock already depends on the new lock.
> > [  107.839631]
> > [  107.839632]
> > [  107.839632] the existing dependency chain (in reverse order) is:
> > [  107.839634]
> > [  107.839634] -> #1 (&mm->mmap_sem){++++++}:
> > [  107.839638]        [<ffffffff8107402d>] lock_acquire+0x8a/0xa7
> > [  107.839642]        [<ffffffff810c3363>] might_fault+0x7b/0x9e
> > [  107.839646]        [<ffffffff810f5246>] filldir+0x6a/0xc2
> > [  107.839649]        [<ffffffff81143b91>] call_filldir+0x91/0xb8
> > [  107.839653]        [<ffffffff81143eb2>] ext4_readdir+0x1b2/0x519
> > [  107.839656]        [<ffffffff810f548c>] vfs_readdir+0x76/0xac
> > [  107.839658]        [<ffffffff810f559e>] sys_getdents+0x79/0xc9
> > [  107.839661]        [<ffffffff813a1fb9>] system_call_fastpath+0x16/0x1b
> > [  107.839665]
> > [  107.839665] -> #0 (&sb->s_type->i_mutex_key#13){+.+.+.}:
> > [  107.839669]        [<ffffffff81073918>] __lock_acquire+0xa81/0xd75
> > [  107.839672]        [<ffffffff8107402d>] lock_acquire+0x8a/0xa7
> > [  107.839675]        [<ffffffff8139acfe>] __mutex_lock_common+0x61/0x456
> > [  107.839679]        [<ffffffff8139b1da>] mutex_lock_nested+0x36/0x3b
> > [  107.839681]        [<ffffffff810ae65a>] generic_file_aio_write+0x45/0xbc
> > [  107.839684]        [<ffffffff8114478e>] ext4_file_write+0x1e2/0x23a
> > [  107.839687]        [<ffffffff810e5bb5>] do_sync_write+0xbd/0xfd
> > [  107.839691]        [<ffffffff810e6333>] vfs_write+0xa7/0xee
> > [  107.839694]        [<ffffffffa037f266>]
> > ecryptfs_write_lower+0x4e/0x73 [ecryptfs]
> > [  107.839700]        [<ffffffffa03803d3>]
> > ecryptfs_encrypt_page+0x11c/0x182 [ecryptfs]
> > [  107.839704]        [<ffffffffa037e967>]
> > ecryptfs_writepage+0x31/0x73 [ecryptfs]
> > [  107.839708]        [<ffffffff810b448b>] __writepage+0x12/0x31
> > [  107.839710]        [<ffffffff810b4b25>] write_cache_pages+0x1e6/0x310
> > [  107.839713]        [<ffffffff810b4c8d>] generic_writepages+0x3e/0x54
> > [  107.839716]        [<ffffffff810b5e05>] do_writepages+0x26/0x28
> > [  107.839719]        [<ffffffff810ae1e4>] __filemap_fdatawrite_range+0x4e/0x50
> > [  107.839722]        [<ffffffff810aed55>] filemap_fdatawrite+0x1a/0x1c
> > [  107.839725]        [<ffffffff810aed72>] filemap_write_and_wait+0x1b/0x36
> > [  107.839727]        [<ffffffffa037c1bb>]
> > ecryptfs_vma_close+0x17/0x19 [ecryptfs]
> > [  107.839731]        [<ffffffff810c9374>] remove_vma+0x3b/0x71
> > [  107.839733]        [<ffffffff810ca40c>] do_munmap+0x2ed/0x306
> > [  107.839735]        [<ffffffff810ca542>] sys_munmap+0x44/0x5b
> > [  107.839738]        [<ffffffff813a1fb9>] system_call_fastpath+0x16/0x1b
> > [  107.839741]
> > [  107.839741] other info that might help us debug this:
> > [  107.839741]
> > [  107.839743]  Possible unsafe locking scenario:
> > [  107.839743]
> > [  107.839744]        CPU0                    CPU1
> > [  107.839746]        ----                    ----
> > [  107.839747]   lock(&mm->mmap_sem);
> > [  107.839749]                                lock(&sb->s_type->i_mutex_key#13);
> > [  107.839753]                                lock(&mm->mmap_sem);
> > [  107.839755]   lock(&sb->s_type->i_mutex_key#13);
> > [  107.839758]
> > [  107.839758]  *** DEADLOCK ***
> > [  107.839759]
> > [  107.839761] 1 lock held by gvfsd-metadata/2314:
> > [  107.839762]  #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff810ca534>]
> > sys_munmap+0x36/0x5b
> > [  107.839767]
> > [  107.839767] stack backtrace:
> > [  107.839769] Pid: 2314, comm: gvfsd-metadata Not tainted 3.3.0-rc6+ #14
> > [  107.839771] Call Trace:
> > [  107.839775]  [<ffffffff813956a2>] print_circular_bug+0x1f8/0x209
> > [  107.839778]  [<ffffffff81073918>] __lock_acquire+0xa81/0xd75
> > [  107.839781]  [<ffffffff81073bfd>] ? __lock_acquire+0xd66/0xd75
> > [  107.839784]  [<ffffffff8107402d>] lock_acquire+0x8a/0xa7
> > [  107.839787]  [<ffffffff810ae65a>] ? generic_file_aio_write+0x45/0xbc
> > [  107.839790]  [<ffffffff8139acfe>] __mutex_lock_common+0x61/0x456
> > [  107.839792]  [<ffffffff810ae65a>] ? generic_file_aio_write+0x45/0xbc
> > [  107.839795]  [<ffffffff81071a96>] ? mark_lock+0x2d/0x258
> > [  107.839798]  [<ffffffff810ae65a>] ? generic_file_aio_write+0x45/0xbc
> > [  107.839801]  [<ffffffff8107299e>] ? lock_is_held+0x92/0x9d
> > [  107.839803]  [<ffffffff8139b1da>] mutex_lock_nested+0x36/0x3b
> > [  107.839806]  [<ffffffff810ae65a>] generic_file_aio_write+0x45/0xbc
> > [  107.839810]  [<ffffffff811a013f>] ? scatterwalk_map+0x2b/0x5d
> > [  107.839813]  [<ffffffff810570d4>] ? get_parent_ip+0xe/0x3e
> > [  107.839816]  [<ffffffff8114478e>] ext4_file_write+0x1e2/0x23a
> > [  107.839818]  [<ffffffff81071a96>] ? mark_lock+0x2d/0x258
> > [  107.839821]  [<ffffffff810e5bb5>] do_sync_write+0xbd/0xfd
> > [  107.839824]  [<ffffffff8139b2fd>] ? __mutex_unlock_slowpath+0x11e/0x152
> > [  107.839828]  [<ffffffff81197092>] ? security_file_permission+0x29/0x2e
> > [  107.839831]  [<ffffffff810e60b2>] ? rw_verify_area+0xab/0xc8
> > [  107.839834]  [<ffffffff810e6333>] vfs_write+0xa7/0xee
> > [  107.839838]  [<ffffffffa037f266>] ecryptfs_write_lower+0x4e/0x73 [ecryptfs]
> > [  107.839842]  [<ffffffffa03803d3>] ecryptfs_encrypt_page+0x11c/0x182
> > [ecryptfs]
> > [  107.839846]  [<ffffffffa037e967>] ecryptfs_writepage+0x31/0x73 [ecryptfs]
> > [  107.839849]  [<ffffffff810b448b>] __writepage+0x12/0x31
> > [  107.839851]  [<ffffffff810b4b25>] write_cache_pages+0x1e6/0x310
> > [  107.839854]  [<ffffffff810b4479>] ? bdi_set_max_ratio+0x6a/0x6a
> > [  107.839857]  [<ffffffff813a03c1>] ? sub_preempt_count+0x90/0xa3
> > [  107.839860]  [<ffffffff810b4c8d>] generic_writepages+0x3e/0x54
> > [  107.839863]  [<ffffffff810b5e05>] do_writepages+0x26/0x28
> > [  107.839866]  [<ffffffff810ae1e4>] __filemap_fdatawrite_range+0x4e/0x50
> > [  107.839869]  [<ffffffff810aed55>] filemap_fdatawrite+0x1a/0x1c
> > [  107.839871]  [<ffffffff810aed72>] filemap_write_and_wait+0x1b/0x36
> > [  107.839875]  [<ffffffffa037c1bb>] ecryptfs_vma_close+0x17/0x19 [ecryptfs]
> > [  107.839877]  [<ffffffff810c9374>] remove_vma+0x3b/0x71
> > [  107.839879]  [<ffffffff810ca40c>] do_munmap+0x2ed/0x306
> > [  107.839882]  [<ffffffff810ca542>] sys_munmap+0x44/0x5b
> > [  107.839884]  [<ffffffff813a1fb9>] system_call_fastpath+0x16/0x1b

^ permalink raw reply	[flat|nested] 7+ messages in thread

end of thread, other threads:[~2012-03-05 22:02 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2012-03-05 21:08 Linus GIT (3.3.0-rc6+) -- INFO: possible circular locking dependency detected Miles Lane
2012-03-05 21:23 ` Andrew Morton
2012-03-05 21:35   ` Al Viro
2012-03-05 21:46     ` Tyler Hicks
2012-03-05 21:33 ` Al Viro
2012-03-05 21:46 ` Ted Ts'o
2012-03-05 22:02   ` Ted Ts'o

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