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>

diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index 2cd1164..9da161c 100644 (file)
--- 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;
 }