Patch "IB/hfi1: Fix defered ack race with qp destroy" has been added to the 4.8-stable tree

This is a note to let you know that I've just added the patch titled

IB/hfi1: Fix defered ack race with qp destroy

to the 4.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ib-hfi1-fix-defered-ack-race-with-qp-destroy.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Mike Marciniszyn <[email protected]>
Date: Sun, 25 Sep 2016 07:41:46 -0700
Subject: IB/hfi1: Fix defered ack race with qp destroy

From: Mike Marciniszyn <[email protected]>

commit 72f53af2651957b0b9d6dead72a393eaf9a2c3be upstream.

There is a a bug in defered ack stuff that causes a race with the destroy of a QP.

A packet causes a defered ack to be pended by putting the QP into an rcd queue.

A return from the driver interrupt processing will process that rcd
queue of QPs and attempt to do a direct send of the ack. At this
point no locks are held and the above QP could now be put in the reset
state in the qp destroy logic. A refcount protects the QP while it
is in the rcd queue so it isn't going anywhere yet.

If the direct send fails to allocate a pio buffer, hfi1_schedule_send() is called to trigger sending an ack from the send engine. There is no state test in that code path.

The refcount is then dropped from the driver.c caller potentially allowing the qp destroy to continue from its refcount wait in parallel with the workqueue scheduling of the qp.

---
 drivers/infiniband/hw/hfi1/rc.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

@@ -932,8 +932,10 @@ void hfi1_send_rc_ack(struct hfi1_ctxtda
 	return;
 
 queue_ack:
-	this_cpu_inc(*ibp->rvp.rc_qacks);
 	spin_lock_irqsave(&qp->s_lock, flags);
+	if (!(ib_rvt_state_ops[qp->state] & RVT_PROCESS_RECV_OK))
+		goto unlock;
+	this_cpu_inc(*ibp->rvp.rc_qacks);
 	qp->s_flags |= RVT_S_ACK_PENDING | RVT_S_RESP_PENDING;
 	qp->s_nak_state = qp->r_nak_state;
 	qp->s_ack_psn = qp->r_ack_psn;

@@ -942,6 +944,7 @@ queue_ack:
 
 	/* Schedule the send tasklet. */
 	hfi1_schedule_send(qp);
+unlock:
 	spin_unlock_irqrestore(&qp->s_lock, flags);
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.8/ib-hfi1-fix-defered-ack-race-with-qp-destroy.patch