linux-kernel - Re: [PATCH] btrfs: use appropriate replacements for __sb_{start,end}

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Date:   Tue, 10 Oct 2017 14:08:11 +0300
From:   Nikolay Borisov <nborisov@...e.com>
To:     Rakesh Pandit <rakesh@...era.com>, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     David Sterba <dsterba@...e.com>, Josef Bacik <jbacik@...com>,
        Chris Mason <clm@...com>
Subject: Re: [PATCH] btrfs: use appropriate replacements for
 __sb_{start,end}_write calls



On 10.10.2017 13:48, Rakesh Pandit wrote:
> Commit a53f4f8e9c8eb ("btrfs: Don't call btrfs_start_transaction() on
> frozen fs to avoid deadlock.") started using internal calls and we
> replace them with more suitable ones.
> 
> Signed-off-by: Rakesh Pandit <rakesh@...era.com>
> ---
>  fs/btrfs/super.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index 35a128a..99c21ae 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -1205,8 +1205,8 @@ int btrfs_sync_fs(struct super_block *sb, int wait)
>  			 * happens. The pending operations are delayed to the
>  			 * next commit after thawing.
>  			 */
> -			if (__sb_start_write(sb, SB_FREEZE_WRITE, false))
> -				__sb_end_write(sb, SB_FREEZE_WRITE);
> +			if (sb_start_write_trylock(sb))
> +				sb_end_write(sb)
>  			else
>  				return 0;

On second thought, what's to prevent the filesystem to be frozen if
sb_start_write/sb_end_write code executes? Or even after we are in the
middle of btrfs_start_transaction?


>  			trans = btrfs_start_transaction(root, 0);
>