[PATCH V2] rdma_rxe: call comp_handler without holding cq->cq_lock

[PATCH V2] rdma_rxe: call comp_handler without holding cq->cq_lock

[Philipp Reisner]

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->cq_lock.

Changelog:
v1: https://lore.kernel.org/all/20250806123921.633410-1-philipp.reisner@linbit.com/
v1 -> v2:
- Only reset cq->notify to 0 when invoking the comp_handler
====================

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>
---
 drivers/infiniband/sw/rxe/rxe_cq.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/sw/rxe/rxe_cq.c b/drivers/infiniband/sw/rxe/rxe_cq.c
index fffd144d509e..95652001665d 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;
+	bool invoke_handler = false;
 
 	spin_lock_irqsave(&cq->cq_lock, flags);
 
@@ -113,11 +114,14 @@ int rxe_cq_post(struct rxe_cq *cq, struct rxe_cqe *cqe, int solicited)
 	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);
+		invoke_handler = true;
 	}
 
 	spin_unlock_irqrestore(&cq->cq_lock, flags);
 
+	if (invoke_handler)
+		cq->ibcq.comp_handler(&cq->ibcq, cq->ibcq.cq_context);
+
 	return 0;
 }
 
-- 
2.50.1