On Wed 02-01-08 12:42:19, Zach Brown wrote:
> Erez Zadok wrote:
> > Setting: ltp-full-20071031, dio01 test on ext3 with Linus's latest tree.
> > Kernel w/ SMP, preemption, and lockdep configured.
>
> This is a real lock ordering problem. Thanks for reporting it.
>
> The updating of atime inside sys_mmap() orders the mmap_sem in the vfs
> outside of the journal handle in ext3's inode dirtying:
>
> > -> #1 (jbd_handle){--..}:
> > [<c023068f>] __lock_acquire+0x9cc/0xb95
> > [<c0230c2f>] lock_acquire+0x5f/0x78
> > [<c029c7e9>] journal_start+0xee/0xf8
> > [<c02959d6>] ext3_journal_start_sb+0x48/0x4a
> > [<c029152b>] ext3_dirty_inode+0x27/0x6c
> > [<c026f701>] __mark_inode_dirty+0x29/0x144
> > [<c026817b>] touch_atime+0xb7/0xbc
> > [<c023af6d>] generic_file_mmap+0x2d/0x42
> > [<c024a5cc>] mmap_region+0x1e6/0x3b4
> > [<c024aa6b>] do_mmap_pgoff+0x1fb/0x253
> > [<c02067af>] sys_mmap2+0x9b/0xb5
> > [<c020275e>] syscall_call+0x7/0xb
> > [<ffffffff>] 0xffffffff
>
> ext3_direct_IO() orders the journal handle outside of the mmap_sem that
> dio_get_page() acquires to pin pages with get_user_pages():
>
> > -> #0 (&mm->mmap_sem){----}:
> > [<c023057f>] __lock_acquire+0x8bc/0xb95
> > [<c0230c2f>] lock_acquire+0x5f/0x78
> > [<c0397d4f>] down_read+0x3a/0x4c
> > [<c02778a2>] dio_get_page+0x4e/0x15d
> > [<c0278352>] __blockdev_direct_IO+0x431/0xa81
> > [<c0291318>] ext3_direct_IO+0x10c/0x1a1
> > [<c023c091>] generic_file_direct_IO+0x124/0x139
> > [<c023c0fc>] generic_file_direct_write+0x56/0x11c
> > [<c023ca15>] __generic_file_aio_write_nolock+0x33d/0x489
> > [<c023cbb9>] generic_file_aio_write+0x58/0xb6
> > [<c028d4e3>] ext3_file_write+0x27/0x99
> > [<c0256d0f>] do_sync_write+0xc5/0x102
> > [<c0257463>] vfs_write+0x90/0x119
> > [<c0257a25>] sys_write+0x3d/0x61
> > [<c02026d6>] sysenter_past_esp+0x5f/0xa5
> > [<ffffffff>] 0xffffffff
>
> Two fixes come to mind:
>
> 1) use something like Peter's ->mmap_prepare() to update atime before
> acquiring the mmap_sem. ( http://lkml.org/lkml/2007/11/11/97 ). I
> don't know if this would leave more paths which do a journal_start()
> while holding the mmap_sem.
>
> 2) rework ext3's dio to only hold the jbd handle in ext3_get_block().
> Chris has a patch for this kicking around somewhere but I'm told it has
> problems exposing old blocks in ordered data mode.
>
> Does anyone have preferences? I could go either way. I certainly don't
> like the idea of journal handles being held across the entirety of
> fs/direct-io.c. It's yet another case of O_DIRECT differing wildly from
> the buffered path :(.
I've looked more into it and I think that 2) is the only way to go since
transaction start ranks below page lock (standard buffered write path) and
page lock ranks below mmap_sem. So we have at least one more dependency
mmap_sem must go before transaction start...
Honza
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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