[PATCH 4/4] sunrpc: lock xprt before trying to set memalloc on the sockets

[Jeff Layton]

It's possible that we could race with a call to xs_reset_transport, in
which case the xprt->inet pointer could be zeroed out while we're
accessing it. Lock the xprt before we try to set memalloc on it.

Cc: Mel Gorman <mgorman@xxxxxxx>
Signed-off-by: Jeff Layton <jeff.layton@xxxxxxxxxxxxxxx>
---
 net/sunrpc/xprtsock.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index 359446442112..91770ccab608 100644
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -1964,11 +1964,22 @@ static void xs_local_connect(struct rpc_xprt *xprt, struct rpc_task *task)
 }
 
 #ifdef CONFIG_SUNRPC_SWAP
+/*
+ * Note that this should be called with XPRT_LOCKED held (or when we otherwise
+ * know that we have exclusive access to the socket), to guard against
+ * races with xs_reset_transport.
+ */
 static void xs_set_memalloc(struct rpc_xprt *xprt)
 {
 	struct sock_xprt *transport = container_of(xprt, struct sock_xprt,
 			xprt);
 
+	/*
+	 * If there's no sock, then we have nothing to set. The
+	 * reconnecting process will get it for us.
+	 */
+	if (!transport->inet)
+		return;
 	if (atomic_read(&xprt->swapper))
 		sk_set_memalloc(transport->inet);
 }
@@ -1986,8 +1997,11 @@ xs_swapper_enable(struct rpc_xprt *xprt)
 	struct sock_xprt *transport = container_of(xprt, struct sock_xprt,
 			xprt);
 
+	if (wait_on_bit_lock(&xprt->state, XPRT_LOCKED, TASK_KILLABLE))
+		return -ERESTARTSYS;
 	if (atomic_inc_return(&xprt->swapper) == 1)
 		sk_set_memalloc(transport->inet);
+	xprt_release_xprt(xprt, NULL);
 	return 0;
 }
 
@@ -2004,8 +2018,11 @@ xs_swapper_disable(struct rpc_xprt *xprt)
 	struct sock_xprt *transport = container_of(xprt, struct sock_xprt,
 			xprt);
 
+	if (wait_on_bit_lock(&xprt->state, XPRT_LOCKED, TASK_UNINTERRUPTIBLE))
+		return;
 	if (atomic_dec_and_test(&xprt->swapper))
 		sk_clear_memalloc(transport->inet);
+	xprt_release_xprt(xprt, NULL);
 }
 #else
 static void xs_set_memalloc(struct rpc_xprt *xprt)
-- 
2.4.1

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