Hi,
my machine got a lockdep warning regarding NFS client on 2.6.31-rc6.
Here is the log:
=======================================================
[ INFO: possible circular locking dependency detected ]
2.6.31-rc6-test #12
-------------------------------------------------------
soffice.bin/31490 is trying to acquire lock:
(&sb->s_type->i_mutex_key#13){+.+.+.}, at: [<f85ea8bb>] nfs_revalidate_mapping+0x72/0xbe [nfs]
but task is already holding lock:
(&mm->mmap_sem){++++++}, at: [<c0106c5b>] sys_mmap2+0x6d/0xb4
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&mm->mmap_sem){++++++}:
[<c0161b06>] __lock_acquire+0x100e/0x130d
[<c0161ebc>] lock_acquire+0xb7/0xeb
[<c01a2a15>] might_fault+0x69/0x9a
[<c026d399>] copy_to_user+0x3c/0x127
[<c01d4427>] filldir64+0xc3/0x108
[<f85e6270>] nfs_do_filldir+0x383/0x4ad [nfs]
[<f85e6b4e>] nfs_readdir+0x7b4/0x830 [nfs]
[<c01d469e>] vfs_readdir+0x76/0xb3
[<c01d474e>] sys_getdents64+0x73/0xc3
[<c0102df3>] sysenter_do_call+0x12/0x38
[<ffffffff>] 0xffffffff
-> #0 (&sb->s_type->i_mutex_key#13){+.+.+.}:
[<c0161856>] __lock_acquire+0xd5e/0x130d
[<c0161ebc>] lock_acquire+0xb7/0xeb
[<c03af059>] mutex_lock_nested+0x43/0x272
[<f85ea8bb>] nfs_revalidate_mapping+0x72/0xbe [nfs]
[<f85e8128>] nfs_file_mmap+0x5e/0x77 [nfs]
[<c01ab5f7>] mmap_region+0x263/0x40f
[<c01aba07>] do_mmap_pgoff+0x264/0x2c7
[<c0106c6f>] sys_mmap2+0x81/0xb4
[<c0102df3>] sysenter_do_call+0x12/0x38
[<ffffffff>] 0xffffffff
other info that might help us debug this:
1 lock held by soffice.bin/31490:
#0: (&mm->mmap_sem){++++++}, at: [<c0106c5b>] sys_mmap2+0x6d/0xb4
stack backtrace:
Pid: 31490, comm: soffice.bin Not tainted 2.6.31-rc6-test #12
Call Trace:
[<c03ad742>] ? printk+0x1d/0x33
[<c01606d1>] print_circular_bug_tail+0xaf/0xcb
[<c0161856>] __lock_acquire+0xd5e/0x130d
[<f85ea8bb>] ? nfs_revalidate_mapping+0x72/0xbe [nfs]
[<c0161ebc>] lock_acquire+0xb7/0xeb
[<f85ea8bb>] ? nfs_revalidate_mapping+0x72/0xbe [nfs]
[<f85ea8bb>] ? nfs_revalidate_mapping+0x72/0xbe [nfs]
[<c03af059>] mutex_lock_nested+0x43/0x272
[<f85ea8bb>] ? nfs_revalidate_mapping+0x72/0xbe [nfs]
[<f8609339>] ? nfs_have_delegation+0x68/0x82 [nfs]
[<f85ea8bb>] nfs_revalidate_mapping+0x72/0xbe [nfs]
[<f85e8128>] nfs_file_mmap+0x5e/0x77 [nfs]
[<c01ab5f7>] mmap_region+0x263/0x40f
[<c01aba07>] do_mmap_pgoff+0x264/0x2c7
[<c0106c6f>] sys_mmap2+0x81/0xb4
[<c0102df3>] sysenter_do_call+0x12/0x38
=======================================================
Indeed this looks like a circular lock dependency since copy_*_user()
invokes mm->mmap_sem mutex lock internally. (I hit a similar bug in
the ALSA core ago, thus I know it :)
The inode lock in vfs_readdir is killable, so it's not critical,
though...
thanks,
Takashi
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