Re: [PATCH v2] block: make bdev_freeze() mutex waits killable

[Jan Kara]

On Wed 11-11-26 20:35:29, diasyzhangqing@xxxxxxxxx wrote:
> From: Qing Zhang <diasyzhang@xxxxxxxxxxx>
> 
> Concurrent bdev_freeze() callers may wait a long time on
> bd_fsfreeze_mutex while another caller freezes and syncs the filesystem.
> Use mutex_lock_killable() to allow fatal signals to interrupt this wait.
> 
> An interrupted wait returns -EINTR before bd_fsfreeze_count is
> incremented, so no freeze reference needs to be dropped. This does not
> make the filesystem freeze operation itself killable.
> 
> Reported-by: syzbot+d4ecb9a1e5b3dcf8baec@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=d4ecb9a1e5b3dcf8baec
> Suggested-by: Jan Kara <jack@xxxxxxx>
> Signed-off-by: Qing Zhang <diasyzhang@xxxxxxxxxxx>

Looks good to me. Feel free to add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

								Honza

> ---
>  Changes since v1:
> - per Jan's suggestion, move the killable wait from a new ext4
>   per-superblock mutex into bdev_freeze() itself.
> 
> block/bdev.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/block/bdev.c b/block/bdev.c
> index f20f91b3176e..e57be2320423 100644
> --- a/block/bdev.c
> +++ b/block/bdev.c
> @@ -301,7 +301,9 @@ int bdev_freeze(struct block_device *bdev)
>  {
>  	int error = 0;
>  
> -	mutex_lock(&bdev->bd_fsfreeze_mutex);
> +	error = mutex_lock_killable(&bdev->bd_fsfreeze_mutex);
> +	if (error)
> +		return error;
>  
>  	/* A device being removed from its filesystem refuses freezes. */
>  	if (!atomic_inc_unless_negative(&bdev->bd_fsfreeze_count)) {
> -- 
> 2.43.7
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR