dax: Fix missed wakeup in put_unlocked_entry()

The condition checking whether put_unlocked_entry() needs to wake up
following waiter got broken by commit 23c84eb7 ("dax: Fix missed
wakeup with PMD faults"). We need to wake the waiter whenever the passed
entry is valid (i.e., non-NULL and not special conflict entry). This
could lead to processes never being woken up when waiting for entry
lock. Fix the condition.

Cc: <stable@vger.kernel.org>
Link: http://lore.kernel.org/r/20190729120228.GC17833@quack2.suse.cz
Fixes: 23c84eb7 ("dax: Fix missed wakeup with PMD faults")
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

fs/dax.c

@@ -266,7 +266,7 @@ static void wait_entry_unlocked(struct xa_state *xas, void *entry)
 static void put_unlocked_entry(struct xa_state *xas, void *entry)
 {
 	/* If we were the only waiter woken, wake the next one */
-	if (entry && dax_is_conflict(entry))
+	if (entry && !dax_is_conflict(entry))
 		dax_wake_entry(xas, entry, false);
 }