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authorDominique Martinet <dominique.martinet@cea.fr>2014-01-17 21:31:00 +0400
committerEric Van Hensbergen <ericvh@gmail.com>2014-03-26 01:37:59 +0400
commit2b6e72ed747f68a038df616efd86744b3644d694 (patch)
treed781427484432608a74ccc44fd4a7a3296751f23 /net/9p/client.c
parent38dbfb59d1175ef458d006556061adeaa8751b72 (diff)
downloadlinux-2b6e72ed747f68a038df616efd86744b3644d694.tar.xz
9P: Add memory barriers to protect request fields over cb/rpc threads handoff
We need barriers to guarantee this pattern works as intended: [w] req->rc, 1 [r] req->status, 1 wmb rmb [w] req->status, 1 [r] req->rc Where the wmb ensures that rc gets written before status, and the rmb ensures that if you observe status == 1, rc is the new value. Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr> Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>
Diffstat (limited to 'net/9p/client.c')
-rw-r--r--net/9p/client.c16
1 files changed, 15 insertions, 1 deletions
diff --git a/net/9p/client.c b/net/9p/client.c
index a5e4d2dcb03e..95b1836173e1 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -415,9 +415,17 @@ static void p9_free_req(struct p9_client *c, struct p9_req_t *r)
* req: request received
*
*/
-void p9_client_cb(struct p9_client *c, struct p9_req_t *req)
+void p9_client_cb(struct p9_client *c, struct p9_req_t *req, int status)
{
p9_debug(P9_DEBUG_MUX, " tag %d\n", req->tc->tag);
+
+ /*
+ * This barrier is needed to make sure any change made to req before
+ * the other thread wakes up will indeed be seen by the waiting side.
+ */
+ smp_wmb();
+ req->status = status;
+
wake_up(req->wq);
p9_debug(P9_DEBUG_MUX, "wakeup: %d\n", req->tc->tag);
}
@@ -751,6 +759,12 @@ again:
err = wait_event_interruptible(*req->wq,
req->status >= REQ_STATUS_RCVD);
+ /*
+ * Make sure our req is coherent with regard to updates in other
+ * threads - echoes to wmb() in the callback
+ */
+ smp_rmb();
+
if ((err == -ERESTARTSYS) && (c->status == Connected)
&& (type == P9_TFLUSH)) {
sigpending = 1;