FAILED: patch "[PATCH] dax: Avoid losing wakeup in dax_lock_mapping_entry" failed to apply to 4.19-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From 25bbe21bf427a81b8e3ccd480ea0e1d940256156 Mon Sep 17 00:00:00 2001
From: Matthew Wilcox <willy@infradead.org>
Date: Fri, 16 Nov 2018 15:50:02 -0500
Subject: [PATCH] dax: Avoid losing wakeup in dax_lock_mapping_entry

After calling get_unlocked_entry(), you have to call
put_unlocked_entry() to avoid subsequent waiters losing wakeups.

Fixes: c2a7d2a11552 ("filesystem-dax: Introduce dax_lock_mapping_entry()")
Cc: stable@vger.kernel.org
Signed-off-by: Matthew Wilcox <willy@infradead.org>

diff --git a/fs/dax.c b/fs/dax.c
index cf2394e2bf4b..9bcce89ea18e 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -391,6 +391,7 @@ bool dax_lock_mapping_entry(struct page *page)
 			rcu_read_unlock();
 			entry = get_unlocked_entry(&xas);
 			xas_unlock_irq(&xas);
+			put_unlocked_entry(&xas, entry);
 			rcu_read_lock();
 			continue;
 		}