linux-kernel - [PATCH] rdma_rxe: call comp_handler without holding cq->cq

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Message-ID: <20250806123921.633410-1-philipp.reisner@linbit.com>
Date: Wed,  6 Aug 2025 14:39:21 +0200
From: Philipp Reisner <philipp.reisner@...bit.com>
To: Zhu Yanjun <zyjzyj2000@...il.com>
Cc: Jason Gunthorpe <jgg@...pe.ca>,
	Leon Romanovsky <leon@...nel.org>,
	linux-rdma@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Philipp Reisner <philipp.reisner@...bit.com>
Subject: [PATCH] rdma_rxe: call comp_handler without holding cq->cq_lock

Allow the comp_handler callback implementation to call ib_poll_cq().
A call to ib_poll_cq() calls rxe_poll_cq() with the rdma_rxe driver.
And rxe_poll_cq() locks cq->cq_lock. That leads to a spinlock deadlock.

The Mellanox and Intel drivers allow a comp_handler callback
implementation to call ib_poll_cq().

Avoid the deadlock by calling the comp_handler callback without
holding cq->cw_lock.

Signed-off-by: Philipp Reisner <philipp.reisner@...bit.com>
---
 drivers/infiniband/sw/rxe/rxe_cq.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/infiniband/sw/rxe/rxe_cq.c b/drivers/infiniband/sw/rxe/rxe_cq.c
index fffd144d509e..1195e109f89b 100644
--- a/drivers/infiniband/sw/rxe/rxe_cq.c
+++ b/drivers/infiniband/sw/rxe/rxe_cq.c
@@ -88,6 +88,7 @@ int rxe_cq_post(struct rxe_cq *cq, struct rxe_cqe *cqe, int solicited)
 	int full;
 	void *addr;
 	unsigned long flags;
+	u8 notify;
 
 	spin_lock_irqsave(&cq->cq_lock, flags);
 
@@ -110,14 +111,15 @@ int rxe_cq_post(struct rxe_cq *cq, struct rxe_cqe *cqe, int solicited)
 
 	queue_advance_producer(cq->queue, QUEUE_TYPE_TO_CLIENT);
 
-	if ((cq->notify & IB_CQ_NEXT_COMP) ||
-	    (cq->notify & IB_CQ_SOLICITED && solicited)) {
-		cq->notify = 0;
-		cq->ibcq.comp_handler(&cq->ibcq, cq->ibcq.cq_context);
-	}
+	notify = cq->notify;
+	cq->notify = 0;
 
 	spin_unlock_irqrestore(&cq->cq_lock, flags);
 
+	if ((notify & IB_CQ_NEXT_COMP) ||
+	    (notify & IB_CQ_SOLICITED && solicited))
+		cq->ibcq.comp_handler(&cq->ibcq, cq->ibcq.cq_context);
+
 	return 0;
 }
 
-- 
2.50.1