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9P: Add memory barriers to protect request fields over cb/rpc threads handoff

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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>
This commit is contained in:
Dominique Martinet
2014-01-17 18:31:00 +01:00
committed by Eric Van Hensbergen
parent 38dbfb59d1
commit 2b6e72ed74
5 changed files with 24 additions and 15 deletions
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16
net/9p/client.c
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@@ -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;