linux-kernel - Re: [PATCH 2/3] fs: make thaw_super

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Date:   Thu, 3 May 2018 17:07:47 +0200
From:   Jan Kara <jack@...e.cz>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     viro@...iv.linux.org.uk, linux-fsdevel@...r.kernel.org,
        jack@...e.cz, bart.vanassche@....com, ming.lei@...hat.com,
        rjw@...ysocki.net, mguzik@...hat.com, linux-pm@...r.kernel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] fs: make thaw_super_locked() really just a helper

On Fri 20-04-18 16:59:03, Luis R. Rodriguez wrote:
> thaw_super_locked() was added via commit 08fdc8a0138a ("buffer.c: call
> thaw_super during emergency thaw") merged on v4.17 to help with the
> ability so that the caller can take charge of handling the s_umount lock,
> however, it has left all* of the failure handling including unlocking
> lock of s_umount inside thaw_super_locked().
> 
> This does not make thaw_super_locked() flexible. For instance we may
> later want to use it with the abilty to handle unfolding of the locks
> ourselves.
> 
> Change thaw_super_locked() to really just be a helper, and let the
> callers deal with all the error handling.

And do you have use for the new thaw_super_locked()? Because the new
semantics with having to deal with deactivate_locked_super() does not seem
ideal either so as a standalone cleanup patch it does not look too
useful.
 
> This commit introeuces no functional changes.
		^^^ introduces
 
								Honza

> ---
>  fs/super.c | 27 ++++++++++++++++++++-------
>  1 file changed, 20 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/super.c b/fs/super.c
> index 9d0eb5e20a1f..82bc74a16f06 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -937,10 +937,15 @@ void emergency_remount(void)
>  
>  static void do_thaw_all_callback(struct super_block *sb)
>  {
> +	int error;
> +
>  	down_write(&sb->s_umount);
>  	if (sb->s_root && sb->s_flags & MS_BORN) {
>  		emergency_thaw_bdev(sb);
> -		thaw_super_locked(sb);
> +		error = thaw_super_locked(sb);
> +		if (error)
> +			up_write(&sb->s_umount);
> +		deactivate_locked_super(sb);
>  	} else {
>  		up_write(&sb->s_umount);
>  	}
> @@ -1532,14 +1537,13 @@ int freeze_super(struct super_block *sb)
>  }
>  EXPORT_SYMBOL(freeze_super);
>  
> +/* Caller takes the sb->s_umount rw_semaphore lock and handles active count */
>  static int thaw_super_locked(struct super_block *sb)
>  {
>  	int error;
>  
> -	if (sb->s_writers.frozen != SB_FREEZE_COMPLETE) {
> -		up_write(&sb->s_umount);
> +	if (sb->s_writers.frozen != SB_FREEZE_COMPLETE)
>  		return -EINVAL;
> -	}
>  
>  	if (sb_rdonly(sb)) {
>  		sb->s_writers.frozen = SB_UNFROZEN;
> @@ -1554,7 +1558,6 @@ static int thaw_super_locked(struct super_block *sb)
>  			printk(KERN_ERR
>  				"VFS:Filesystem thaw failed\n");
>  			lockdep_sb_freeze_release(sb);
> -			up_write(&sb->s_umount);
>  			return error;
>  		}
>  	}
> @@ -1563,7 +1566,6 @@ static int thaw_super_locked(struct super_block *sb)
>  	sb_freeze_unlock(sb);
>  out:
>  	wake_up(&sb->s_writers.wait_unfrozen);
> -	deactivate_locked_super(sb);
>  	return 0;
>  }
>  
> @@ -1575,7 +1577,18 @@ static int thaw_super_locked(struct super_block *sb)
>   */
>  int thaw_super(struct super_block *sb)
>  {
> +	int error;
> +
>  	down_write(&sb->s_umount);
> -	return thaw_super_locked(sb);
> +	error = thaw_super_locked(sb);
> +	if (error) {
> +		up_write(&sb->s_umount);
> +		goto out;
> +	}
> +
> +	deactivate_locked_super(sb);
> +
> +out:
> +	return error;
>  }
>  EXPORT_SYMBOL(thaw_super);
> -- 
> 2.16.3
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR