[PATCH v2 2/5] sunrpc: make xprt->swapper an atomic_t

Jeff Layton
2015-06-03T14:44:13Z

Split xs_swapper into enable/disable functions and eliminate the
"enable" flag.

Currently, it's racy if you have multiple swapon/swapoff operations
running in parallel over the same xprt. Also fix it so that we only
set it to a memalloc socket on a 0->1 transition and only clear it
on a 1->0 transition.

Cc: Mel Gorman <mgorman@suse.de>
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
---
include/linux/sunrpc/xprt.h | 5 +++--
net/sunrpc/clnt.c | 4 ++--
net/sunrpc/xprtsock.c | 38 +++++++++++++++++++++++++-------------
3 files changed, 30 insertions(+), 17 deletions(-)

diff --git a/include/linux/sunrpc/xprt.h b/include/linux/sunrpc/xprt.h
index 8b93ef53df3c..26b1624128ec 100644
--- a/include/linux/sunrpc/xprt.h
+++ b/include/linux/sunrpc/xprt.h
@@ -180,7 +180,7 @@ struct rpc_xprt {
atomic_t num_reqs; /* total slots */
unsigned long state; /* transport state */
unsigned char resvport : 1; /* use a reserved port */
- unsigned int swapper; /* we're swapping over this
+ atomic_t swapper; /* we're swapping over this
transport */
unsigned int bind_index; /* bind function index */

@@ -345,7 +345,8 @@ void xprt_release_rqst_cong(struct rpc_task *task);
void xprt_disconnect_done(struct rpc_xprt *xprt);
void xprt_force_disconnect(struct rpc_xprt *xprt);
void xprt_conditional_disconnect(struct rpc_xprt *xprt, unsigned int cookie);
-int xs_swapper(struct rpc_xprt *xprt, int enable);
+int xs_swapper_enable(struct rpc_xprt *xprt);
+void xs_swapper_disable(struct rpc_xprt *xprt);

bool xprt_lock_connect(struct rpc_xprt *, struct rpc_task *, void *);
void xprt_unlock_connect(struct rpc_xprt *, void *);
diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index 383cb778179f..804a75e71e84 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -2492,7 +2492,7 @@ retry:
goto retry;
}

- ret = xs_swapper(xprt, 1);
+ ret = xs_swapper_enable(xprt);
xprt_put(xprt);
}
return ret;
@@ -2519,7 +2519,7 @@ retry:
goto retry;
}

- xs_swapper(xprt, 0);
+ xs_swapper_disable(xprt);
xprt_put(xprt);
}
}
diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index b29703996028..a2861bbfd319 100644
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -1966,31 +1966,43 @@ static void xs_set_memalloc(struct rpc_xprt *xprt)
struct sock_xprt *transport = container_of(xprt, struct sock_xprt,
xprt);

- if (xprt->swapper)
+ if (atomic_read(&xprt->swapper))
sk_set_memalloc(transport->inet);
}

/**
- * xs_swapper - Tag this transport as being used for swap.
+ * xs_swapper_enable - Tag this transport as being used for swap.
* @xprt: transport to tag
- * @enable: enable/disable
*
+ * Take a reference to this transport on behalf of the rpc_clnt, and
+ * optionally mark it for swapping if it wasn't already.
*/
-int xs_swapper(struct rpc_xprt *xprt, int enable)
+int
+xs_swapper_enable(struct rpc_xprt *xprt)
{
struct sock_xprt *transport = container_of(xprt, struct sock_xprt,
xprt);
- int err = 0;

- if (enable) {
- xprt->swapper++;
- xs_set_memalloc(xprt);
- } else if (xprt->swapper) {
- xprt->swapper--;
- sk_clear_memalloc(transport->inet);
- }
+ if (atomic_inc_return(&xprt->swapper) == 1)
+ sk_set_memalloc(transport->inet);
+ return 0;
+}

- return err;
+/**
+ * xs_swapper_disable - Untag this transport as being used for swap.
+ * @xprt: transport to tag
+ *
+ * Drop a "swapper" reference to this xprt on behalf of the rpc_clnt. If the
+ * swapper refcount goes to 0, untag the socket as a memalloc socket.
+ */
+void
+xs_swapper_disable(struct rpc_xprt *xprt)
+{
+ struct sock_xprt *transport = container_of(xprt, struct sock_xprt,
+ xprt);
+
+ if (atomic_dec_and_test(&xprt->swapper))
+ sk_clear_memalloc(transport->inet);
}
#else
static void xs_set_memalloc(struct rpc_xprt *xprt)