Re: Review: Fix dbflush panic in xfs_qm_sync

[Lachlan McIlroy <lachlan@xxxxxxx>]

Could mp->m_quotainfo become NULL after this check but before we
lock the list with xfs_qm_mplist_lock()?  There doesn't seem to
be any locking to protect changes to this field?

Donald Douwsma wrote:
> The recent behaviour layer removal dropped the check for quotas that 
> have been
> requested at mount time but have subsequently been turned off. This results
> in a panic when accessing m_quotainfo which has been freed.
>
> This patch adds the check originally made by xfs_qm_syncall() to 
> xfs_qm_sync()
>
> Signed-off-by: Donald Douwsma <donaldd@xxxxxxx>
>
> --- 2.6.x-xfs.orig/fs/xfs/quota/xfs_qm.c
> +++ 2.6.x-xfs/fs/xfs/quota/xfs_qm.c
> @@ -1007,6 +1007,9 @@ xfs_qm_sync(
>      boolean_t    nowait;
>      int        error;
>
> +    if (! XFS_IS_QUOTA_ON(mp))
> +        return 0;
> +
>      restarts = 0;
>      /*
>       * We won't block unless we are asked to.