dax: Use non-exclusive wait in wait_entry_unlocked()

commit d8a706414af4827fc0b4b1c0c631c607351938b9 upstream.

get_unlocked_entry() uses an exclusive wait because it is guaranteed to
eventually obtain the lock and follow on with an unlock+wakeup cycle.
The wait_entry_unlocked() path does not have the same guarantee. Rather
than open-code an extra wakeup, just switch to a non-exclusive wait.

Cc: Matthew Wilcox <willy@infradead.org>
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/dax.c b/fs/dax.c
index 415605f..09fa706 100644 (file)
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -275,18 +275,16 @@ static void wait_entry_unlocked(struct address_space *mapping, pgoff_t index,
        ewait.wait.func = wake_exceptional_entry_func;
 
        wq = dax_entry_waitqueue(mapping, index, entry, &ewait.key);
-       prepare_to_wait_exclusive(wq, &ewait.wait, TASK_UNINTERRUPTIBLE);
+       /*
+        * Unlike get_unlocked_entry() there is no guarantee that this
+        * path ever successfully retrieves an unlocked entry before an
+        * inode dies. Perform a non-exclusive wait in case this path
+        * never successfully performs its own wake up.
+        */
+       prepare_to_wait(wq, &ewait.wait, TASK_UNINTERRUPTIBLE);
        xa_unlock_irq(&mapping->i_pages);
        schedule();
        finish_wait(wq, &ewait.wait);
-
-       /*
-        * Entry lock waits are exclusive. Wake up the next waiter since
-        * we aren't sure we will acquire the entry lock and thus wake
-        * the next waiter up on unlock.
-        */
-       if (waitqueue_active(wq))
-               __wake_up(wq, TASK_NORMAL, 1, &ewait.key);
 }
 
 static void unlock_mapping_entry(struct address_space *mapping, pgoff_t index)