From: Benjamin Marzinski <bmarzins@redhat.com>
Date: Mon, 8 Jun 2009 18:05:32 -0500
Subject: [gfs2] get gfs2meta superblock correctly
Message-id: 20090608230532.GI9501@ether.msp.redhat.com
O-Subject: [RHEL-5.4 PATCH] BZ#504086 gfs2: Get gfs2meta superblock correctly.
Bugzilla: 504086
RH-Acked-by: Steven Whitehouse <swhiteho@redhat.com>
RH-Acked-by: Bob Peterson <rpeterso@redhat.com>

The way gfs2 grabbed the superblock was incorrect. It did not
follow the common locking scheme and it also didn't lock the s_umount
rw semaphore.  This caused a problem were once a gfs2meta filesystem was
mounted, unmounts would hang.  This patch makes gfs2 use the
sget() to get an active reference to the superblock.

This fix is already upstream:
http://git.kernel.org/?p=linux/kernel/git/steve/gfs2-2.6-nmw.git;a=commitdiff;h=f6d03139d745198b434f65a28aabed524f415a4c

This patch has been tested with multiple mount/unmount combinations.

Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>

diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index 6f833c3..b0e9fea 100644
--- a/fs/gfs2/ops_fstype.c
+++ b/fs/gfs2/ops_fstype.c
@@ -1101,9 +1101,20 @@ static int gfs2_get_sb(struct file_system_type *fs_type, int flags,
 	return get_sb_bdev(fs_type, flags, dev_name, data, fill_super, mnt);
 }
 
+static int test_meta_super(struct super_block *s, void *ptr)
+{
+	struct block_device *bdev = ptr;
+	return (bdev == s->s_bdev);
+}
+
+static int set_meta_super(struct super_block *s, void *ptr)
+{
+	return -EINVAL;
+}
+
 static struct super_block *get_gfs2_sb(const char *dev_name)
 {
-	struct super_block *sb;
+	struct super_block *s;
 	struct nameidata nd;
 	int error;
 
@@ -1111,30 +1122,27 @@ static struct super_block *get_gfs2_sb(const char *dev_name)
 	if (error) {
 		printk(KERN_WARNING "GFS2: path_lookup on %s returned error %d\n",
 			dev_name, error);
-		return NULL;
+		return ERR_PTR(-ENOENT);
 	}
-	sb = nd.dentry->d_inode->i_sb;
-	if (sb && (sb->s_type == &gfs2_fs_type))
-		atomic_inc(&sb->s_active);
-	else
-		sb = NULL;
+	s = sget(&gfs2_fs_type, test_meta_super, set_meta_super,
+		 nd.dentry->d_inode->i_sb->s_bdev);
 	path_release(&nd);
-	return sb;
+	return s;
 }
 
 static int gfs2_get_sb_meta(struct file_system_type *fs_type, int flags,
 			    const char *dev_name, void *data, struct vfsmount *mnt)
 {
-	struct super_block *sb = NULL;
+	struct super_block *s;
 	struct gfs2_sbd *sdp;
 
-	sb = get_gfs2_sb(dev_name);
-	if (!sb) {
+	s = get_gfs2_sb(dev_name);
+	if (IS_ERR(s)) {
 		printk(KERN_WARNING "GFS2: gfs2 mount does not exist\n");
-		return -ENOENT;
+		return PTR_ERR(s);
 	}
-	sdp = (struct gfs2_sbd*) sb->s_fs_info;
-	mnt->mnt_sb = sb;
+	sdp = s->s_fs_info;
+	mnt->mnt_sb = s;
 	mnt->mnt_root = dget(sdp->sd_master_dir);
 	return 0;
 }