linux-kernel - Re: [PATCH V2 2/2] fs: print a message when freezing/unfreezing filesystems

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Message-ID: <20140514111449.GB5824@quack.suse.cz>
Date:	Wed, 14 May 2014 13:14:49 +0200
From:	Jan Kara <jack@...e.cz>
To:	Mateusz Guzik <mguzik@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Josef Bacik <jbacik@...com>, Jan Kara <jack@...e.cz>,
	Al Viro <viro@...IV.linux.org.uk>,
	Eric Sandeen <esandeen@...hat.com>,
	Joe Perches <joe@...ches.com>
Subject: Re: [PATCH V2 2/2] fs: print a message when freezing/unfreezing
 filesystems

On Wed 14-05-14 00:04:43, Mateusz Guzik wrote:
> This helps hang troubleshooting efforts when only dmesg is available.
> 
> While here remove code duplication with MS_RDONLY case and fix a
> whitespace nit.
  I'm somewhat undecided here I have to say. On one hand I don't like
printing to kernel log when everything is fine and kernel is operating
normally. On the other hand I've seen quite a few cases where people have
shot themselves in the foot with filesystem freezing so having some trace
of this in the log doesn't seem like a completely bad thing either. What do
other people think?

								Honza
> Signed-off-by: Mateusz Guzik <mguzik@...hat.com>
> Cc: linux-fsdevel@...r.kernel.org
> Cc: Josef Bacik <jbacik@...com>
> Cc: Jan Kara <jack@...e.cz>
> Cc: Al Viro <viro@...IV.linux.org.uk>
> Cc: Eric Sandeen <esandeen@...hat.com>
> Cc: Joe Perches <joe@...ches.com>
> ---
> since v1:
> 	fix copy-pasto which found its way into the patch
> 	restore curly brackets in MS_RDONLY case
>  fs/super.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/super.c b/fs/super.c
> index 017e10a..4dd7356 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -1291,9 +1291,7 @@ int freeze_super(struct super_block *sb)
>  
>  	if (sb->s_flags & MS_RDONLY) {
>  		/* Nothing to do really... */
> -		sb->s_writers.frozen = SB_FREEZE_COMPLETE;
> -		up_write(&sb->s_umount);
> -		return 0;
> +		goto out;
>  	}
>  
>  	/* From now on, no new normal writers can start */
> @@ -1335,8 +1333,10 @@ int freeze_super(struct super_block *sb)
>  	 * This is just for debugging purposes so that fs can warn if it
>  	 * sees write activity when frozen is set to SB_FREEZE_COMPLETE.
>  	 */
> +out:
>  	sb->s_writers.frozen = SB_FREEZE_COMPLETE;
>  	up_write(&sb->s_umount);
> +	pr_info("VFS:Filesystem %s frozen\n", sb->s_id);
>  	return 0;
>  }
>  EXPORT_SYMBOL(freeze_super);
> @@ -1374,7 +1374,7 @@ out:
>  	smp_wmb();
>  	wake_up(&sb->s_writers.wait_unfrozen);
>  	deactivate_locked_super(sb);
> -
> +	pr_info("VFS:Filesystem %s thawed\n", sb->s_id);
>  	return 0;
>  }
>  EXPORT_SYMBOL(thaw_super);
> -- 
> 1.8.3.1
> 
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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