linux-kernel - [PATCH 4.2.y-ckt 160/211] xprtrdma: Re-arm after missed events

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Message-Id: <1452023119-25647-161-git-send-email-kamal@canonical.com>
Date:	Tue,  5 Jan 2016 11:44:28 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Chuck Lever <chuck.lever@...cle.com>,
	Anna Schumaker <Anna.Schumaker@...app.com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 160/211] xprtrdma: Re-arm after missed events

4.2.8-ckt1 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Chuck Lever <chuck.lever@...cle.com>

commit 7b3d770c67bc07db5035999e4f864c5f2ff7b10e upstream.

ib_req_notify_cq(IB_CQ_REPORT_MISSED_EVENTS) returns a positive
value if WCs were added to a CQ after the last completion upcall
but before the CQ has been re-armed.

Commit 7f23f6f6e388 ("xprtrmda: Reduce lock contention in
completion handlers") assumed that when ib_req_notify_cq() returned
a positive RC, the CQ had also been successfully re-armed, making
it safe to return control to the provider without losing any
completion signals. That is an invalid assumption.

Change both completion handlers to continue polling while
ib_req_notify_cq() returns a positive value.

Fixes: 7f23f6f6e388 ("xprtrmda: Reduce lock contention in ...")
Signed-off-by: Chuck Lever <chuck.lever@...cle.com>
Reviewed-by: Sagi Grimberg <sagig@...lanox.com>
Reviewed-by: Devesh Sharma <devesh.sharma@...gotech.com>
Tested-By: Devesh Sharma <devesh.sharma@...gotech.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@...app.com>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 net/sunrpc/xprtrdma/verbs.c | 66 +++++++--------------------------------------
 1 file changed, 10 insertions(+), 56 deletions(-)

diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
index 891c4ed..e0eece6 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c
@@ -178,38 +178,17 @@ rpcrdma_sendcq_poll(struct ib_cq *cq, struct rpcrdma_ep *ep)
 	return 0;
 }
 
-/*
- * Handle send, fast_reg_mr, and local_inv completions.
- *
- * Send events are typically suppressed and thus do not result
- * in an upcall. Occasionally one is signaled, however. This
- * prevents the provider's completion queue from wrapping and
- * losing a completion.
+/* Handle provider send completion upcalls.
  */
 static void
 rpcrdma_sendcq_upcall(struct ib_cq *cq, void *cq_context)
 {
 	struct rpcrdma_ep *ep = (struct rpcrdma_ep *)cq_context;
-	int rc;
-
-	rc = rpcrdma_sendcq_poll(cq, ep);
-	if (rc) {
-		dprintk("RPC:       %s: ib_poll_cq failed: %i\n",
-			__func__, rc);
-		return;
-	}
 
-	rc = ib_req_notify_cq(cq,
-			IB_CQ_NEXT_COMP | IB_CQ_REPORT_MISSED_EVENTS);
-	if (rc == 0)
-		return;
-	if (rc < 0) {
-		dprintk("RPC:       %s: ib_req_notify_cq failed: %i\n",
-			__func__, rc);
-		return;
-	}
-
-	rpcrdma_sendcq_poll(cq, ep);
+	do {
+		rpcrdma_sendcq_poll(cq, ep);
+	} while (ib_req_notify_cq(cq, IB_CQ_NEXT_COMP |
+				  IB_CQ_REPORT_MISSED_EVENTS) > 0);
 }
 
 static void
@@ -273,42 +252,17 @@ out_schedule:
 	return rc;
 }
 
-/*
- * Handle receive completions.
- *
- * It is reentrant but processes single events in order to maintain
- * ordering of receives to keep server credits.
- *
- * It is the responsibility of the scheduled tasklet to return
- * recv buffers to the pool. NOTE: this affects synchronization of
- * connection shutdown. That is, the structures required for
- * the completion of the reply handler must remain intact until
- * all memory has been reclaimed.
+/* Handle provider receive completion upcalls.
  */
 static void
 rpcrdma_recvcq_upcall(struct ib_cq *cq, void *cq_context)
 {
 	struct rpcrdma_ep *ep = (struct rpcrdma_ep *)cq_context;
-	int rc;
-
-	rc = rpcrdma_recvcq_poll(cq, ep);
-	if (rc) {
-		dprintk("RPC:       %s: ib_poll_cq failed: %i\n",
-			__func__, rc);
-		return;
-	}
 
-	rc = ib_req_notify_cq(cq,
-			IB_CQ_NEXT_COMP | IB_CQ_REPORT_MISSED_EVENTS);
-	if (rc == 0)
-		return;
-	if (rc < 0) {
-		dprintk("RPC:       %s: ib_req_notify_cq failed: %i\n",
-			__func__, rc);
-		return;
-	}
-
-	rpcrdma_recvcq_poll(cq, ep);
+	do {
+		rpcrdma_recvcq_poll(cq, ep);
+	} while (ib_req_notify_cq(cq, IB_CQ_NEXT_COMP |
+				  IB_CQ_REPORT_MISSED_EVENTS) > 0);
 }
 
 static void
-- 
1.9.1

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