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

[NeilBrown <neilb@suse.com>]

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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@suse.com>
---
 net/sunrpc/cache.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

I found this when I was looking for something else.  Testing hasn't
shown a bug, and nor has it shown that this is bug-free.  But it looks
right.

NeilBrown


diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index 273bc3a35425..008c25d1b9f9 100644
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -1182,14 +1182,14 @@ 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);
-- 
2.7.0


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