linux-kernel - Re: [PATCH 02/11] fs: provide unlocked helper thaw

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Date:   Thu, 30 Nov 2017 17:59:48 +0100
From:   Jan Kara <jack@...e.cz>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     viro@...iv.linux.org.uk, bart.vanassche@....com,
        ming.lei@...hat.com, tytso@....edu, darrick.wong@...cle.com,
        jikos@...nel.org, rjw@...ysocki.net, pavel@....cz,
        len.brown@...el.com, linux-fsdevel@...r.kernel.org,
        boris.ostrovsky@...cle.com, jgross@...e.com,
        todd.e.brandt@...ux.intel.com, nborisov@...e.com, jack@...e.cz,
        martin.petersen@...cle.com, ONeukum@...e.com,
        oleksandr@...alenko.name, oleg.b.antonyan@...il.com,
        yu.chen.surf@...il.com, dan.j.williams@...el.com,
        linux-pm@...r.kernel.org, linux-block@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/11] fs: provide unlocked helper thaw_super()

On Wed 29-11-17 15:23:47, Luis R. Rodriguez wrote:
> thaw_super() hold a write lock, however we wish to also enable
> callers which already hold the write lock. To do this provide a helper
> and make thaw_super() use it. This way, all that thaw_super() does
> now is lock handling and active count management.
> 
> This change has no functional changes.
> 
> Suggested-by: Dave Chinner <david@...morbit.com>
> Signed-off-by: Luis R. Rodriguez <mcgrof@...nel.org>

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/super.c | 39 ++++++++++++++++++++++++++-------------
>  1 file changed, 26 insertions(+), 13 deletions(-)
> 
> diff --git a/fs/super.c b/fs/super.c
> index a7650ff22f0e..cecc279beecd 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -1493,21 +1493,13 @@ int freeze_super(struct super_block *sb)
>  }
>  EXPORT_SYMBOL(freeze_super);
>  
> -/**
> - * thaw_super -- unlock filesystem
> - * @sb: the super to thaw
> - *
> - * Unlocks the filesystem and marks it writeable again after freeze_super().
> - */
> -int thaw_super(struct super_block *sb)
> +/* Caller takes lock and handles active count */
> +static int thaw_locked_super(struct super_block *sb)
>  {
>  	int error;
>  
> -	down_write(&sb->s_umount);
> -	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;
> @@ -1522,7 +1514,6 @@ int thaw_super(struct super_block *sb)
>  			printk(KERN_ERR
>  				"VFS:Filesystem thaw failed\n");
>  			lockdep_sb_freeze_release(sb);
> -			up_write(&sb->s_umount);
>  			return error;
>  		}
>  	}
> @@ -1531,7 +1522,29 @@ int thaw_super(struct super_block *sb)
>  	sb_freeze_unlock(sb);
>  out:
>  	wake_up(&sb->s_writers.wait_unfrozen);
> -	deactivate_locked_super(sb);
>  	return 0;
>  }
> +
> +/**
> + * thaw_super -- unlock filesystem
> + * @sb: the super to thaw
> + *
> + * Unlocks the filesystem and marks it writeable again after freeze_super().
> + */
> +int thaw_super(struct super_block *sb)
> +{
> +	int error;
> +
> +	down_write(&sb->s_umount);
> +	error = thaw_locked_super(sb);
> +	if (error) {
> +		up_write(&sb->s_umount);
> +		goto out;
> +	}
> +
> +	deactivate_locked_super(sb);
> +
> +out:
> +	return error;
> +}
>  EXPORT_SYMBOL(thaw_super);
> -- 
> 2.15.0
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR