ocfs2: ocfs2_inode_lock_tracker does not distinguish lock level

ocfs2_inode_lock_tracker as a variant of ocfs2_inode_lock, is used to
prevent deadlock due to recursive lock acquisition.

But this function does not distinguish whether the requested level is EX
or PR.

If a RP lock has been attained, this function will immediately return
success afterwards even an EX lock is requested.

But actually the return value does not mean that the process got a EX
lock, because ocfs2_inode_lock has not been called.

When taking lock levels into account, we face some different situations:

1. no lock is held
   In this case, just lock the inode and return 0

2. We are holding a lock
   For this situation, things diverges into several cases

   wanted     holding	     what to do
   ex		ex	    see 2.1 below
   ex		pr	    see 2.2 below
   pr		ex	    see 2.1 below
   pr		pr	    see 2.1 below

   2.1 lock level that is been held is compatible
   with the wanted level, so no lock action will be tacken.

   2.2 Otherwise, an upgrade is needed, but it is forbidden.

Reason why upgrade within a process is forbidden is that lock upgrade
may cause dead lock.  The following illustrate how it happens.

        process 1                             process 2
ocfs2_inode_lock_tracker(ex=0)
                               <======   ocfs2_inode_lock_tracker(ex=1)

ocfs2_inode_lock_tracker(ex=1)

For the status quo of ocfs2, without this patch, neither a bug nor
end-user impact will be caused because the wrong logic is avoided.

But I'm afraid this generic interface, may be called by other developers
in future and used in this situation.

  a process
ocfs2_inode_lock_tracker(ex=0)
ocfs2_inode_lock_tracker(ex=1)

Link: http://lkml.kernel.org/r/20180510053230.17217-1-lchen@suse.com
Signed-off-by: Larry Chen <lchen@suse.com>
Reviewed-by: Gang He <ghe@suse.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Joseph Qi <jiangqi903@gmail.com>
Cc: Changwei Ge <ge.changwei@h3c.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ocfs2/dlmglue.c

@@ -788,35 +788,34 @@ static inline void ocfs2_add_holder(struct ocfs2_lock_res *lockres,
 	spin_unlock(&lockres->l_lock);
 }
 
-static inline void ocfs2_remove_holder(struct ocfs2_lock_res *lockres,
-				       struct ocfs2_lock_holder *oh)
-{
-	spin_lock(&lockres->l_lock);
-	list_del(&oh->oh_list);
-	spin_unlock(&lockres->l_lock);
-
-	put_pid(oh->oh_owner_pid);
-}
-
-static inline int ocfs2_is_locked_by_me(struct ocfs2_lock_res *lockres)
+static struct ocfs2_lock_holder *
+ocfs2_pid_holder(struct ocfs2_lock_res *lockres,
+		struct pid *pid)
 {
 	struct ocfs2_lock_holder *oh;
-	struct pid *pid;
 
-	/* look in the list of holders for one with the current task as owner */
 	spin_lock(&lockres->l_lock);
-	pid = task_pid(current);
 	list_for_each_entry(oh, &lockres->l_holders, oh_list) {
 		if (oh->oh_owner_pid == pid) {
 			spin_unlock(&lockres->l_lock);
-			return 1;
+			return oh;
 		}
 	}
 	spin_unlock(&lockres->l_lock);
+	return NULL;
+}
 
-	return 0;
+static inline void ocfs2_remove_holder(struct ocfs2_lock_res *lockres,
+				       struct ocfs2_lock_holder *oh)
+{
+	spin_lock(&lockres->l_lock);
+	list_del(&oh->oh_list);
+	spin_unlock(&lockres->l_lock);
+
+	put_pid(oh->oh_owner_pid);
 }
 
+
 static inline void ocfs2_inc_holders(struct ocfs2_lock_res *lockres,
 				     int level)
 {
@@ -2610,34 +2609,93 @@ void ocfs2_inode_unlock(struct inode *inode,
  *
  * return < 0 on error, return == 0 if there's no lock holder on the stack
  * before this call, return == 1 if this call would be a recursive locking.
+ * return == -1 if this lock attempt will cause an upgrade which is forbidden.
+ *
+ * When taking lock levels into account,we face some different situations.
+ *
+ * 1. no lock is held
+ *    In this case, just lock the inode as requested and return 0
+ *
+ * 2. We are holding a lock
+ *    For this situation, things diverges into several cases
+ *
+ *    wanted     holding	     what to do
+ *    ex		ex	    see 2.1 below
+ *    ex		pr	    see 2.2 below
+ *    pr		ex	    see 2.1 below
+ *    pr		pr	    see 2.1 below
+ *
+ *    2.1 lock level that is been held is compatible
+ *    with the wanted level, so no lock action will be tacken.
+ *
+ *    2.2 Otherwise, an upgrade is needed, but it is forbidden.
+ *
+ * Reason why upgrade within a process is forbidden is that
+ * lock upgrade may cause dead lock. The following illustrates
+ * how it happens.
+ *
+ *         thread on node1                             thread on node2
+ * ocfs2_inode_lock_tracker(ex=0)
+ *
+ *                                <======   ocfs2_inode_lock_tracker(ex=1)
+ *
+ * ocfs2_inode_lock_tracker(ex=1)
  */
 int ocfs2_inode_lock_tracker(struct inode *inode,
 			     struct buffer_head **ret_bh,
 			     int ex,
 			     struct ocfs2_lock_holder *oh)
 {
-	int status;
-	int arg_flags = 0, has_locked;
+	int status = 0;
 	struct ocfs2_lock_res *lockres;
+	struct ocfs2_lock_holder *tmp_oh;
+	struct pid *pid = task_pid(current);
+
 
 	lockres = &OCFS2_I(inode)->ip_inode_lockres;
-	has_locked = ocfs2_is_locked_by_me(lockres);
-	/* Just get buffer head if the cluster lock has been taken */
-	if (has_locked)
-		arg_flags = OCFS2_META_LOCK_GETBH;
+	tmp_oh = ocfs2_pid_holder(lockres, pid);
 
-	if (likely(!has_locked || ret_bh)) {
-		status = ocfs2_inode_lock_full(inode, ret_bh, ex, arg_flags);
+	if (!tmp_oh) {
+		/*
+		 * This corresponds to the case 1.
+		 * We haven't got any lock before.
+		 */
+		status = ocfs2_inode_lock_full(inode, ret_bh, ex, 0);
 		if (status < 0) {
 			if (status != -ENOENT)
 				mlog_errno(status);
 			return status;
 		}
-	}
-	if (!has_locked)
+
+		oh->oh_ex = ex;
 		ocfs2_add_holder(lockres, oh);
+		return 0;
+	}
 
-	return has_locked;
+	if (unlikely(ex && !tmp_oh->oh_ex)) {
+		/*
+		 * case 2.2 upgrade may cause dead lock, forbid it.
+		 */
+		mlog(ML_ERROR, "Recursive locking is not permitted to "
+		     "upgrade to EX level from PR level.\n");
+		dump_stack();
+		return -EINVAL;
+	}
+
+	/*
+	 *  case 2.1 OCFS2_META_LOCK_GETBH flag make ocfs2_inode_lock_full.
+	 *  ignore the lock level and just update it.
+	 */
+	if (ret_bh) {
+		status = ocfs2_inode_lock_full(inode, ret_bh, ex,
+					       OCFS2_META_LOCK_GETBH);
+		if (status < 0) {
+			if (status != -ENOENT)
+				mlog_errno(status);
+			return status;
+		}
+	}
+	return tmp_oh ? 1 : 0;
 }
 
 void ocfs2_inode_unlock_tracker(struct inode *inode,
@@ -2649,12 +2707,13 @@ void ocfs2_inode_unlock_tracker(struct inode *inode,
 
 	lockres = &OCFS2_I(inode)->ip_inode_lockres;
 	/* had_lock means that the currect process already takes the cluster
-	 * lock previously. If had_lock is 1, we have nothing to do here, and
-	 * it will get unlocked where we got the lock.
+	 * lock previously.
+	 * If had_lock is 1, we have nothing to do here.
+	 * If had_lock is 0, we will release the lock.
 	 */
 	if (!had_lock) {
+		ocfs2_inode_unlock(inode, oh->oh_ex);
 		ocfs2_remove_holder(lockres, oh);
-		ocfs2_inode_unlock(inode, ex);
 	}
 }
 

fs/ocfs2/dlmglue.h

@@ -96,6 +96,7 @@ struct ocfs2_trim_fs_info {
 struct ocfs2_lock_holder {
 	struct list_head oh_list;
 	struct pid *oh_owner_pid;
+	int oh_ex;
 };
 
 /* ocfs2_inode_lock_full() 'arg_flags' flags */