On Fri, Jul 20, 2018 at 11:46:10AM -0700, Omar Sandoval wrote:
> From: Josef Bacik <jbacik@xxxxxx>
>
> We recently ran into the following deadlock involving
> btrfs_write_inode():
>
> [ +0.005066] __schedule+0x38e/0x8c0
> [ +0.007144] schedule+0x36/0x80
> [ +0.006447] bit_wait+0x11/0x60
> [ +0.006446] __wait_on_bit+0xbe/0x110
> [ +0.007487] ? bit_wait_io+0x60/0x60
> [ +0.007319] __inode_wait_for_writeback+0x96/0xc0
> [ +0.009568] ? autoremove_wake_function+0x40/0x40
> [ +0.009565] inode_wait_for_writeback+0x21/0x30
> [ +0.009224] evict+0xb0/0x190
> [ +0.006099] iput+0x1a8/0x210
> [ +0.006103] btrfs_run_delayed_iputs+0x73/0xc0
> [ +0.009047] btrfs_commit_transaction+0x799/0x8c0
> [ +0.009567] btrfs_write_inode+0x81/0xb0
> [ +0.008008] __writeback_single_inode+0x267/0x320
> [ +0.009569] writeback_sb_inodes+0x25b/0x4e0
> [ +0.008702] wb_writeback+0x102/0x2d0
> [ +0.007487] wb_workfn+0xa4/0x310
> [ +0.006794] ? wb_workfn+0xa4/0x310
> [ +0.007143] process_one_work+0x150/0x410
> [ +0.008179] worker_thread+0x6d/0x520
> [ +0.007490] kthread+0x12c/0x160
> [ +0.006620] ? put_pwq_unlocked+0x80/0x80
> [ +0.008185] ? kthread_park+0xa0/0xa0
> [ +0.007484] ? do_syscall_64+0x53/0x150
> [ +0.007837] ret_from_fork+0x29/0x40
>
> Writeback calls btrfs_write_inode(), which calls
> btrfs_commit_transaction(), which calls btrfs_run_delayed_iputs(). If
> iput() is called on that same inode, evict() will wait for writeback
> forever.
>
> btrfs_write_inode() was originally added way back in 4730a4bc5bf3
> ("btrfs_dirty_inode") to support O_SYNC writes. However, ->write_inode()
> hasn't been used for O_SYNC since 148f948ba877 ("vfs: Introduce new
> helpers for syncing after writing to O_SYNC file or IS_SYNC inode"), so
> btrfs_write_inode() is actually unnecessary (and leads to a bunch of
> unnecessary commits). Get rid of it, which also gets rid of the
> deadlock.
>
> Signed-off-by: Josef Bacik <jbacik@xxxxxx>
> [Omar: new commit message]
> Signed-off-by: Omar Sandoval <osandov@xxxxxx>
Thank, added to current 4.19 queue and I'll add tags for stable.
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