[3.16.y-ckt stable] Patch "sunrpc/cache: drop reference when sunrpc_cache_pipe_upcall() detects a race" has been added to the 3.16.y-ckt tree

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    sunrpc/cache: drop reference when sunrpc_cache_pipe_upcall() detects a race

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt27.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

---8<------------------------------------------------------------

>From 9e54c463b1bbd26856eea198081a657d1f3556c8 Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb at suse.com>
Date: Fri, 4 Mar 2016 17:20:13 +1100
Subject: sunrpc/cache: drop reference when sunrpc_cache_pipe_upcall() detects
 a race

commit a6ab1e8126d205238defbb55d23661a3a5c6a0d8 upstream.

sunrpc_cache_pipe_upcall() can detect a race if CACHE_PENDING is no longer
set.  In this case it aborts the queuing of the upcall.
However it has already taken a new counted reference on "h" and
doesn't "put" it, even though it frees the data structure holding the reference.

So let's delay the "cache_get" until we know we need it.

Fixes: f9e1aedc6c79 ("sunrpc/cache: remove races with queuing an upcall.")
Signed-off-by: NeilBrown <neilb at suse.com>
Signed-off-by: J. Bruce Fields <bfields at redhat.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/sunrpc/cache.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index 14d38ec5e53d..11e7b55f04e2 100644
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -1187,14 +1187,14 @@ int sunrpc_cache_pipe_upcall(struct cache_detail *detail, struct cache_head *h)
 	}

 	crq->q.reader = 0;
-	crq->item = cache_get(h);
 	crq->buf = buf;
 	crq->len = 0;
 	crq->readers = 0;
 	spin_lock(&queue_lock);
-	if (test_bit(CACHE_PENDING, &h->flags))
+	if (test_bit(CACHE_PENDING, &h->flags)) {
+		crq->item = cache_get(h);
 		list_add_tail(&crq->q.list, &detail->queue);
-	else
+	} else
 		/* Lost a race, no longer PENDING, so don't enqueue */
 		ret = -EAGAIN;
 	spin_unlock(&queue_lock);