Re: 3.1.0-rc3 -- INFO: possible circular locking dependency detected

[Josh Boyer]

On Tue, Aug 23, 2011 at 12:39 AM, Miles Lane <miles.lane@xxxxxxxxx> wrote:
> [ INFO: possible circular locking dependency detected ]
> 3.1.0-rc3 #2
> -------------------------------------------------------
> dconf-service/1836 is trying to acquire lock:
>  (&sb->s_type->i_mutex_key#12){+.+.+.}, at: [<ffffffff8116df1a>]
> ext4_evict_inode+0x88/0x32b
>
>  but task is already holding lock:
>  (&mm->mmap_sem){++++++}, at: [<ffffffff810d4393>] sys_munmap+0x36/0x5b
>
> which lock already depends on the new lock.
>
> the existing dependency chain (in reverse order) is:
>
> -> #1 (&mm->mmap_sem){++++++}:
>       [<ffffffff8106933a>] lock_acquire+0x129/0x14e
>       [<ffffffff810cddbd>] might_fault+0x68/0x8b
>       [<ffffffff810fcf5e>] filldir+0x6a/0xc2
>       [<ffffffff811651a1>] call_filldir+0x91/0xb8
>       [<ffffffff811654bf>] ext4_readdir+0x1af/0x510
>       [<ffffffff810fd1a4>] vfs_readdir+0x76/0xac
>       [<ffffffff810fd2b6>] sys_getdents+0x79/0xc9
>       [<ffffffff814162fb>] system_call_fastpath+0x16/0x1b
>
> -> #0 (&sb->s_type->i_mutex_key#12){+.+.+.}:
>       [<ffffffff81068b10>] __lock_acquire+0xa5e/0xd52
>       [<ffffffff8106933a>] lock_acquire+0x129/0x14e
>       [<ffffffff8140f1a2>] __mutex_lock_common+0x64/0x413
>       [<ffffffff8140f5b0>] mutex_lock_nested+0x16/0x18
>       [<ffffffff8116df1a>] ext4_evict_inode+0x88/0x32b
>       [<ffffffff81102d8a>] evict+0x94/0x14e
>       [<ffffffff81102fd0>] iput+0x18c/0x195
>       [<ffffffff810ffdd4>] dentry_kill+0x11e/0x140
>       [<ffffffff8110019b>] dput+0xd4/0xe4
>       [<ffffffff810efac3>] fput+0x1a5/0x1bd
>       [<ffffffff810d3214>] remove_vma+0x37/0x5f
>       [<ffffffff810d4239>] do_munmap+0x2ed/0x306
>       [<ffffffff810d43a1>] sys_munmap+0x44/0x5b
>       [<ffffffff814162fb>] system_call_fastpath+0x16/0x1b
>
> other info that might help us debug this:
>
>  Possible unsafe locking scenario:
>
>       CPU0                    CPU1
>       ----                    ----
>  lock(&mm->mmap_sem);
>                               lock(&sb->s_type->i_mutex_key);
>                               lock(&mm->mmap_sem);
>  lock(&sb->s_type->i_mutex_key);
>
>  *** DEADLOCK ***

This one was reported yesterday: https://lkml.org/lkml/2011/8/21/163
and we're hoping Ted (or someone else from the ext4 camp) can comment
on why ext4_evict_inode is holding i_mutex.

josh
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