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SubjectRe: [PATCH 4/4] sunrpc: lock xprt before trying to set memalloc on the sockets
On Sat, 30 May 2015 08:03:13 -0400
Jeff Layton <jlayton@poochiereds.net> wrote:

> 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);

Oh, we need to check that transport->inet is not NULL before we call
sk_set/clear_memalloc on it. I'll respin with that fix once I give
everyone a chance to comment on the rest...

> + 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)


--
Jeff Layton <jlayton@poochiereds.net>


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