GFS2: Fix use-after-free bug on umount

There was a use-after-free with the GFS2 super block during
umount. This patch moves almost all of the umount code from
->put_super into ->kill_sb, the only bit that cannot be moved
being the glock hash clearing which has to remain as ->put_super
due to umount ordering requirements. As a result its now obvious
that the kfree is the final operation, whereas before it was
hidden in ->put_super.

Also gfs2_jindex_free is then only referenced from a single file
so thats moved and marked static too.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/glock.c

@@ -1547,8 +1547,9 @@ static void clear_glock(struct gfs2_glock *gl)
  * Called when unmounting the filesystem.
  */
 
-void gfs2_gl_hash_clear(struct gfs2_sbd *sdp)
+void gfs2_gl_hash_clear(struct super_block *sb)
 {
+	struct gfs2_sbd *sdp = sb->s_fs_info;
 	unsigned long t;
 	unsigned int x;
 	int cont;