linux-kernel - Re: [PATCH 1/1] fs: fix lock imbalance in do_remount

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Date:	Wed, 13 May 2009 16:08:20 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jiri Slaby <jirislaby@...il.com>
Cc:	viro@...iv.linux.org.uk, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, jirislaby@...il.com
Subject: Re: [PATCH 1/1] fs: fix lock imbalance in do_remount_sb()

On Wed, 13 May 2009 21:21:12 +0200
Jiri Slaby <jirislaby@...il.com> wrote:

> Commit "Push BKL down into do_remount_sb()" pushed un/lock_kernel
> into do_remount_sb but forgets to unlock it on fail paths. Fix
> that.
> 

argh, how many times must we teach ourselves this lesson?  Perhaps we
can convert this function to have a single `return' to prevent
relapses?

> ---
>  fs/super.c |   12 +++++++++---
>  1 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/super.c b/fs/super.c
> index e4a0c5b..a64f362 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -548,18 +548,24 @@ int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
>  	if ((flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY)) {
>  		if (force)
>  			mark_files_ro(sb);
> -		else if (!fs_may_remount_ro(sb))
> +		else if (!fs_may_remount_ro(sb)) {
> +			unlock_kernel();
>  			return -EBUSY;
> +		}
>  		retval = vfs_dq_off(sb, 1);
> -		if (retval < 0 && retval != -ENOSYS)
> +		if (retval < 0 && retval != -ENOSYS) {
> +			unlock_kernel();
>  			return -EBUSY;

Strange that the code drops the vfs_dq_off() return value on the floor.
`man(2) mount' lists a great pile of possible errnos.

> +		}
>  	}
>  	remount_rw = !(flags & MS_RDONLY) && (sb->s_flags & MS_RDONLY);
>  
>  	if (sb->s_op->remount_fs) {
>  		retval = sb->s_op->remount_fs(sb, &flags, data);
> -		if (retval)
> +		if (retval) {
> +			unlock_kernel();
>  			return retval;
> +		}


>  	}
>  	sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) | (flags & MS_RMT_MASK);
>  	unlock_kernel();

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