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Subject[PATCH 4/4] sunrpc: lock xprt before trying to set memalloc on the sockets
Date
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@suse.de>
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
---
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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