cifs: simplify refcounting for oplock breaks

Currently, we take a sb->s_active reference and a cifsFileInfo reference
when an oplock break workqueue job is queued. This is unnecessary and
more complicated than it needs to be. Also as Al points out,
deactivate_super has non-trivial locking implications so it's best to
avoid that if we can.

Instead, just cancel any pending oplock breaks for this filehandle
synchronously in cifsFileInfo_put after taking it off the lists.
That should ensure that this job doesn't outlive the structures it
depends on.

Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/cifsfs.c

@@ -86,24 +86,6 @@ extern mempool_t *cifs_sm_req_poolp;
 extern mempool_t *cifs_req_poolp;
 extern mempool_t *cifs_mid_poolp;
 
-void
-cifs_sb_active(struct super_block *sb)
-{
-	struct cifs_sb_info *server = CIFS_SB(sb);
-
-	if (atomic_inc_return(&server->active) == 1)
-		atomic_inc(&sb->s_active);
-}
-
-void
-cifs_sb_deactive(struct super_block *sb)
-{
-	struct cifs_sb_info *server = CIFS_SB(sb);
-
-	if (atomic_dec_and_test(&server->active))
-		deactivate_super(sb);
-}
-
 static int
 cifs_read_super(struct super_block *sb)
 {