Re: [PATCH] reiserfs: Fix locking in reiserfs_quota_on()

[Frederic Weisbecker <fweisbec@gmail.com>]

On Thu, Oct 28, 2010 at 02:28:23AM +0200, Jan Kara wrote:
> reiserfs_quota_on() unpacks a tail of quota file in case it has one. But after
> BKL conversion, reiserfs_unpack() expects to be called with write_lock held.
> So acquire the lock before calling reiserfs_unpack() to avoid assertion
> failures.
> 
> Reported-by: markus.gapp@gmx.net
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
>  fs/reiserfs/super.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
>  Frederic, would you merge this patch or should I merge it?
> 
> diff --git a/fs/reiserfs/super.c b/fs/reiserfs/super.c
> index 6e85cfd..73c000f 100644
> --- a/fs/reiserfs/super.c
> +++ b/fs/reiserfs/super.c
> @@ -2059,7 +2059,9 @@ static int reiserfs_quota_on(struct super_block *sb, int type, int format_id,
>  	inode = path->dentry->d_inode;
>  	/* We must not pack tails for quota files on reiserfs for quota IO to work */
>  	if (!(REISERFS_I(inode)->i_flags & i_nopack_mask)) {
> +		reiserfs_write_lock(sb);
>  		err = reiserfs_unpack(inode, NULL);
> +		reiserfs_write_unlock(sb);
>  		if (err) {
>  			reiserfs_warning(sb, "super-6520",
>  				"Unpacking tail of quota file failed"
> -- 
> 1.7.1
> 



Yeah. This is due to a recent fix in reiserfs_unpack().
And in this fix I assumed reiserfs_unpack() was always called under the
reiserfs lock.
I was wrong, I thought that reiserfs_quota_on() was ok because it can
call joural_begin() which appears to have the same requirements.
But no that's probably another bug, journal_begin() should also
be called under the reiserfs lock.
Anyway that must be another patch.


For this specific problem, it might be slightly more proper to do the
below. It lowers a bit the reiserfs lock coverage and also fixes
a weird lock-unlock ordering in reiserfs_unpack() that was doing:

	Lock A - Lock B - Unlock A - Unlock B

Hmm?


diff --git a/fs/reiserfs/ioctl.c b/fs/reiserfs/ioctl.c
index 5cbb81e..af2a58f 100644
--- a/fs/reiserfs/ioctl.c
+++ b/fs/reiserfs/ioctl.c
@@ -189,8 +189,8 @@ int reiserfs_unpack(struct inode *inode, struct file *filp)
 	/* we need to make sure nobody is changing the file size beneath
 	 ** us
 	 */
-	reiserfs_mutex_lock_safe(&inode->i_mutex, inode->i_sb);
 	depth = reiserfs_write_lock_once(inode->i_sb);
+	reiserfs_mutex_lock_safe(&inode->i_mutex, inode->i_sb);
 
 	write_from = inode->i_size & (blocksize - 1);
 	/* if we are on a block boundary, we are already unpacked.  */