Re: [PATCH] gfs2: Get rid of I_MUTEX_QUOTA usage

[Steven Whitehouse <swhiteho@redhat.com>]

Hi,

On Thu, 2012-04-26 at 15:20 +0200, Jan Kara wrote:
> GFS2 uses i_mutex on its system quota inode to synchronize writes to
> quota file. Since this is an internal inode to GFS2 (not part of directory
> hiearchy or visible by user) we are safe to define locking rules for it. So
> let's just get it its own locking class to make it clear.
> 
It is visible to the user if the gfs2 metadata filesystem is mounted.
That used to be the way in which the quotas were set by gfs2_quota.
However that is really considered obsolete now, so maybe we don't have
to support that interface any more... the gfs2_quota package is no
longer in distros as the generic quota package does the job for us these
days.

I'd just been looking at using sd_quota_mutex instead of the inode
mutex, but run into that same issue,

Steve.


> CC: Steven Whitehouse <swhiteho@redhat.com>
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
>  fs/gfs2/ops_fstype.c |    8 ++++++++
>  fs/gfs2/quota.c      |    2 +-
>  2 files changed, 9 insertions(+), 1 deletions(-)
> 
>  So this is probably the simplest what can be done for GFS2 (actually OCFS2
> does the same for internal system files). Compile tested only. Steven?
> 
> diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
> index 6f3a18f..ae8f225 100644
> --- a/fs/gfs2/ops_fstype.c
> +++ b/fs/gfs2/ops_fstype.c
> @@ -19,6 +19,7 @@
>  #include <linux/mount.h>
>  #include <linux/gfs2_ondisk.h>
>  #include <linux/quotaops.h>
> +#include <linux/lockdep.h>
>  
>  #include "gfs2.h"
>  #include "incore.h"
> @@ -767,6 +768,7 @@ fail:
>  	return error;
>  }
>  
> +static struct lock_class_key gfs2_quota_imutex_key;
>  
>  static int init_inodes(struct gfs2_sbd *sdp, int undo)
>  {
> @@ -804,6 +806,12 @@ static int init_inodes(struct gfs2_sbd *sdp, int undo)
>  		fs_err(sdp, "can't get quota file inode: %d\n", error);
>  		goto fail_rindex;
>  	}
> +	/*
> +	 * i_mutex on quota files is special. Since this inode is hidden system
> +	 * file, we are safe to define locking ourselves.
> +	 */
> +	lockdep_set_class(&sdp->sd_quota_inode->i_mutex,
> +			  &gfs2_quota_imutex_key);
>  
>  	error = gfs2_rindex_update(sdp);
>  	if (error)
> diff --git a/fs/gfs2/quota.c b/fs/gfs2/quota.c
> index 6019da3..970598b 100644
> --- a/fs/gfs2/quota.c
> +++ b/fs/gfs2/quota.c
> @@ -772,7 +772,7 @@ static int do_sync(unsigned int num_qd, struct gfs2_quota_data **qda)
>  		return -ENOMEM;
>  
>  	sort(qda, num_qd, sizeof(struct gfs2_quota_data *), sort_qd, NULL);
> -	mutex_lock_nested(&ip->i_inode.i_mutex, I_MUTEX_QUOTA);
> +	mutex_lock(&ip->i_inode.i_mutex);
>  	for (qx = 0; qx < num_qd; qx++) {
>  		error = gfs2_glock_nq_init(qda[qx]->qd_gl, LM_ST_EXCLUSIVE,
>  					   GL_NOCACHE, &ghs[qx]);