linux-kernel - [PATCH 3.12 26/76] sunrpc/cache: drop reference when sunrpc_cache_pipe

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Date:	Thu, 19 May 2016 11:07:48 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, NeilBrown <neilb@...e.com>,
	"J . Bruce Fields" <bfields@...hat.com>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 26/76] sunrpc/cache: drop reference when sunrpc_cache_pipe_upcall() detects a race

From: NeilBrown <neilb@...e.com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

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@...e.com>
Signed-off-by: J. Bruce Fields <bfields@...hat.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 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 f3e2b7d8f325..b81e0a33a8be 100644
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -1189,14 +1189,14 @@ 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);
-- 
2.8.2