linux-ext4 - Re: [PATCH V2] jbd2: flush_descriptor(): Do not decrease buffer head's ref count

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Date:   Thu, 8 Aug 2019 11:50:40 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Chandan Rajendra <chandan@...ux.ibm.com>
Cc:     linux-ext4@...r.kernel.org, adilger.kernel@...ger.ca,
        harish@...ux.ibm.com, jack@...e.cz
Subject: Re: [PATCH V2] jbd2: flush_descriptor(): Do not decrease buffer
 head's ref count

On Mon, Aug 05, 2019 at 09:38:00AM +0530, Chandan Rajendra wrote:
> When executing generic/388 on a ppc64le machine, we notice the following
> call trace,
> 
> VFS: brelse: Trying to free free buffer
> WARNING: CPU: 0 PID: 6637 at /root/repos/linux/fs/buffer.c:1195 __brelse+0x84/0xc0
> 
> Call Trace:
>  __brelse+0x80/0xc0 (unreliable)
>  invalidate_bh_lru+0x78/0xc0
>  on_each_cpu_mask+0xa8/0x130
>  on_each_cpu_cond_mask+0x130/0x170
>  invalidate_bh_lrus+0x44/0x60
>  invalidate_bdev+0x38/0x70
>  ext4_put_super+0x294/0x560
>  generic_shutdown_super+0xb0/0x170
>  kill_block_super+0x38/0xb0
>  deactivate_locked_super+0xa4/0xf0
>  cleanup_mnt+0x164/0x1d0
>  task_work_run+0x110/0x160
>  do_notify_resume+0x414/0x460
>  ret_from_except_lite+0x70/0x74
> 
> The warning happens because flush_descriptor() drops bh reference it
> does not own. The bh reference acquired by
> jbd2_journal_get_descriptor_buffer() is owned by the log_bufs list and
> gets released when this list is processed. The reference for doing IO is
> only acquired in write_dirty_buffer() later in flush_descriptor().
> 
> Reported-by: Harish Sriram <harish@...ux.ibm.com>
> Reviewed-by: Jan Kara <jack@...e.cz>
> Signed-off-by: Chandan Rajendra <chandan@...ux.ibm.com>

Thanks, applied.

					- Ted