Re: [PATCH] fs/ext4: fix ABBA deadlock in ext4_rmdir()

[Sergey Senozhatsky <senozhatsky@chromium.org>]

On (26/08/27 21:50), Sergey Senozhatsky wrote:
> We observe the following ABBA deadlock (casefolding enabled):
> 
>  INFO: task jbd2/dm-13-8:447 blocked for more than 720 seconds.
>  task:jbd2/dm-13-8    state:D stack:0     pid:447   tgid:447   ppid:2
>  Call Trace:
>   <TASK>
>   __schedule+0xc2c/0xe60
>   schedule+0x40/0xe0
>   jbd2_journal_wait_updates+0x8f/0xf0
>   jbd2_journal_commit_transaction+0x321/0x1850
>   kjournald2+0xa9/0x230
>   kthread+0x226/0x2a0
>   ret_from_fork+0x101/0x1e0
>   ret_from_fork_asm+0x1a/0x30
> 
>  INFO: task Thread-10:4161 blocked for more than 720 seconds.
>  task:Thread-10       state:D stack:0     pid:4161  tgid:3848  ppid:540
>  Call Trace:
>   <TASK>
>   __schedule+0xc2c/0xe60
>   schedule+0x40/0xe0
>   wait_transaction_locked+0x8c/0xd0
>   start_this_handle+0x252/0x870
>   jbd2__journal_start+0x120/0x280
>   __ext4_journal_start_sb+0x11a/0x250
>   ext4_evict_inode+0x208/0x760
>   iput+0x222/0x5c0
>   dput+0x293/0x690
>   ____fput+0x145/0x2b0
>   task_work_run+0x7a/0xb0
>   exit_to_user_mode_loop+0xc0/0xd0
>   do_syscall_64+0x14b/0xf10
>   entry_SYSCALL_64_after_hwframe+0x76/0x7e
> 
>  NMI backtrace for cpu 0
>  CPU: 0 UID: 1010216 PID: 4160 Comm: Thread-7
>  RIP: 0010:d_walk+0x0/0x290
> [..]
>  Call Trace:
>  <TASK>
>   shrink_dcache_parent+0xb2/0x100
>   d_invalidate+0x50/0x110
>   ext4_rmdir+0x3a2/0x3d0
>   vfs_rmdir+0x9d/0x1d0
>   do_rmdir+0xf0/0x330
>   __x64_sys_unlinkat+0x34/0x50
>   do_syscall_64+0x61/0xf10
> 
> The problem is that ext4_rmdir() calls d_invalidate() before stopping
> the jbd2 transaction handle.  Because d_invalidate() traverses child
> dentries it can encounter dying or in-use dentries.  If a concurrent
> thread executing __dentry_kill() on a child dentry invokes ext4_evict_inode(),
> it requests a new transaction handle via ext4_journal_start(), which
> waits for all running handles to close.  However, the thread executing
> ext4_rmdir() still holds its active transaction handle while looping
> in shrink_dcache_parent() waiting for the dying child dentry to complete
> eviction.
> 
> Stop transaction handle in ext4_rmdir() before calling d_invalidate().

Hello,

I'm not sure I see this patch in linux-next, has it fell through the
cracks?