Re: dio_get_page() lockdep complaints

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 19 Apr 2007 09:38:30 +0200 Jens Axboe <jens.axboe@oracle.com> wrote:

> Hi,
> 
> Doing some testing on CFQ, I ran into this 100% reproducible report:
> 
> =======================================================
> [ INFO: possible circular locking dependency detected ]
> 2.6.21-rc7 #5
> -------------------------------------------------------
> fio/9741 is trying to acquire lock:
>  (&mm->mmap_sem){----}, at: [<b018cb34>] dio_get_page+0x54/0x161
> 
> but task is already holding lock:
>  (&inode->i_mutex){--..}, at: [<b038c6e5>] mutex_lock+0x1c/0x1f
> 
> which lock already depends on the new lock.
> 

This is the correct ranking: i_mutex outside mmap_sem.

> 
> the existing dependency chain (in reverse order) is:
> 
> -> #1 (&inode->i_mutex){--..}:
>        [<b013e3fb>] __lock_acquire+0xdee/0xf9c
>        [<b013e600>] lock_acquire+0x57/0x70
>        [<b038c4a5>] __mutex_lock_slowpath+0x73/0x297
>        [<b038c6e5>] mutex_lock+0x1c/0x1f
>        [<b01b17e9>] reiserfs_file_release+0x54/0x447
>        [<b016afe7>] __fput+0x53/0x101
>        [<b016b0ee>] fput+0x19/0x1c
>        [<b015bcd5>] remove_vma+0x3b/0x4d
>        [<b015c659>] do_munmap+0x17f/0x1cf
>        [<b015c6db>] sys_munmap+0x32/0x42
>        [<b0103f04>] sysenter_past_esp+0x5d/0x99
>        [<ffffffff>] 0xffffffff
> 
> -> #0 (&mm->mmap_sem){----}:
>        [<b013e259>] __lock_acquire+0xc4c/0xf9c
>        [<b013e600>] lock_acquire+0x57/0x70
>        [<b0137b92>] down_read+0x3a/0x4c
>        [<b018cb34>] dio_get_page+0x54/0x161
>        [<b018d7a9>] __blockdev_direct_IO+0x514/0xe2a
>        [<b01cf449>] ext3_direct_IO+0x98/0x1e5
>        [<b014e8df>] generic_file_direct_IO+0x63/0x133
>        [<b01500e9>] generic_file_aio_read+0x16b/0x222
>        [<b017f8b6>] aio_rw_vect_retry+0x5a/0x116
>        [<b0180147>] aio_run_iocb+0x69/0x129
>        [<b0180a78>] io_submit_one+0x194/0x2eb
>        [<b0181331>] sys_io_submit+0x92/0xe7
>        [<b0103f90>] syscall_call+0x7/0xb
>        [<ffffffff>] 0xffffffff

But here reiserfs is taking i_mutex in its file_operations.release(), which
can be called under mmap_sem.

Vladimir's recent de14569f94513279e3d44d9571a421e9da1759ae.  "resierfs:
avoid tail packing if an inode was ever mmapped" comes real close to this
code, but afaict it did not cause this bug.

I can't think of anything which we've done in the 2.6.21 cycle which would have
caused this to start happening.  Odd.


> The test run was fio, the job file used is:
> 
> # fio job file snip below
> [global]
> bs=4k
> buffered=0
> ioengine=libaio
> iodepth=4
> thread
> 
> [readers]
> numjobs=8
> size=128m
> rw=read
> # fio job file snip above
> 
> Filesystem was ext3, default mkfs and mount options. Kernel was
> 2.6.21-rc7 as of this morning, with some CFQ patches applied.
> 

It's interesting that lockdep learned the (wrong) ranking from a reiserfs
operation then later detected it being violated by ext3.

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