GFS2: Fix locking issue mounting gfs2meta fs

This patch uses sget() to get a reference to the
existing gfs2 sb when mouting the gfs2meta filesystem
(in fact thats just another mount of the gfs2
filesystem with a different root and this interface
is for backward compatibility).

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Reported-by: Benjamin Marzinski <bmarzins@redhat.com>
Tested-by: Benjamin Marzinski <bmarzins@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>

1 files changed, 22 insertions, 14 deletions

diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index 2cd1164c88d7..9da161cbb30f 100644
--- a/fs/gfs2/ops_fstype.c
+++ b/fs/gfs2/ops_fstype.c
@@ -1273,9 +1273,20 @@ 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 path path;
         int error;
 
@@ -1283,30 +1294,27 @@ 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 = path.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,
+                 path.dentry->d_inode->i_sb->s_bdev);
         path_put(&path);
-        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 = 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;
 }