linux-kernel - [PATCH 4.14 018/118] iw_cxgb4: atomically flush the qp

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Message-Id: <20180115123416.342638302@linuxfoundation.org>
Date:   Mon, 15 Jan 2018 13:34:05 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Steve Wise <swise@...ngridcomputing.com>,
        Doug Ledford <dledford@...hat.com>
Subject: [PATCH 4.14 018/118] iw_cxgb4: atomically flush the qp

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

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

From: Steve Wise <swise@...ngridcomputing.com>

commit bc52e9ca74b9a395897bb640c6671b2cbf716032 upstream.

__flush_qp() has a race condition where during the flush operation,
the qp lock is released allowing another thread to possibly post a WR,
which corrupts the queue state, possibly causing crashes.  The lock was
released to preserve the cq/qp locking hierarchy of cq first, then qp.
However releasing the qp lock is not necessary; both RQ and SQ CQ locks
can be acquired first, followed by the qp lock, and then the RQ and SQ
flushing can be done w/o unlocking.

Signed-off-by: Steve Wise <swise@...ngridcomputing.com>
Signed-off-by: Doug Ledford <dledford@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/infiniband/hw/cxgb4/qp.c |   19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

--- a/drivers/infiniband/hw/cxgb4/qp.c
+++ b/drivers/infiniband/hw/cxgb4/qp.c
@@ -1271,31 +1271,34 @@ static void __flush_qp(struct c4iw_qp *q
 
 	pr_debug("%s qhp %p rchp %p schp %p\n", __func__, qhp, rchp, schp);
 
-	/* locking hierarchy: cq lock first, then qp lock. */
+	/* locking hierarchy: cqs lock first, then qp lock. */
 	spin_lock_irqsave(&rchp->lock, flag);
+	if (schp != rchp)
+		spin_lock(&schp->lock);
 	spin_lock(&qhp->lock);
 
 	if (qhp->wq.flushed) {
 		spin_unlock(&qhp->lock);
+		if (schp != rchp)
+			spin_unlock(&schp->lock);
 		spin_unlock_irqrestore(&rchp->lock, flag);
 		return;
 	}
 	qhp->wq.flushed = 1;
+	t4_set_wq_in_error(&qhp->wq);
 
 	c4iw_flush_hw_cq(rchp);
 	c4iw_count_rcqes(&rchp->cq, &qhp->wq, &count);
 	rq_flushed = c4iw_flush_rq(&qhp->wq, &rchp->cq, count);
-	spin_unlock(&qhp->lock);
-	spin_unlock_irqrestore(&rchp->lock, flag);
 
-	/* locking hierarchy: cq lock first, then qp lock. */
-	spin_lock_irqsave(&schp->lock, flag);
-	spin_lock(&qhp->lock);
 	if (schp != rchp)
 		c4iw_flush_hw_cq(schp);
 	sq_flushed = c4iw_flush_sq(qhp);
+
 	spin_unlock(&qhp->lock);
-	spin_unlock_irqrestore(&schp->lock, flag);
+	if (schp != rchp)
+		spin_unlock(&schp->lock);
+	spin_unlock_irqrestore(&rchp->lock, flag);
 
 	if (schp == rchp) {
 		if (t4_clear_cq_armed(&rchp->cq) &&
@@ -1329,8 +1332,8 @@ static void flush_qp(struct c4iw_qp *qhp
 	rchp = to_c4iw_cq(qhp->ibqp.recv_cq);
 	schp = to_c4iw_cq(qhp->ibqp.send_cq);
 
-	t4_set_wq_in_error(&qhp->wq);
 	if (qhp->ibqp.uobject) {
+		t4_set_wq_in_error(&qhp->wq);
 		t4_set_cq_in_error(&rchp->cq);
 		spin_lock_irqsave(&rchp->comp_handler_lock, flag);
 		(*rchp->ibcq.comp_handler)(&rchp->ibcq, rchp->ibcq.cq_context);