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Thu, 25 Sep 2025 12:57:12 -0700 (PDT) From: Philipp Reisner To: Zhu Yanjun Cc: Jason Gunthorpe , Leon Romanovsky , linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org, Philipp Reisner Subject: [PATCH V3] rdma_rxe: call comp_handler without holding cq->cq_lock Date: Thu, 25 Sep 2025 21:56:40 +0200 Message-ID: <20250925195640.32594-1-philipp.reisner@linbit.com> X-Mailer: git-send-email 2.50.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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. Other InfiniBand drivers call the comp_handler callback from a single thread, in the RXE driver, acquiring the cq->cq_lock has achieved that up to now. As that gets removed, introduce a new lock dedicated to making the execution of the comp_handler single-threaded. Changelog: v2 -> v3: - make execution of comp_handler single-threaded v2: https://lore.kernel.org/lkml/20250822081941.989520-1-philipp.reisner@l= inbit.com/ v1 -> v2: - Only reset cq->notify to 0 when invoking the comp_handler v1: https://lore.kernel.org/all/20250806123921.633410-1-philipp.reisner@li= nbit.com/ =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Signed-off-by: Philipp Reisner Reviewed-by: Zhu Yanjun --- drivers/infiniband/sw/rxe/rxe_cq.c | 10 +++++++++- drivers/infiniband/sw/rxe/rxe_verbs.h | 1 + 2 files changed, 10 insertions(+), 1 deletion(-) diff --git a/drivers/infiniband/sw/rxe/rxe_cq.c b/drivers/infiniband/sw/rxe= /rxe_cq.c index fffd144d509e..8d94cef7bd50 100644 --- a/drivers/infiniband/sw/rxe/rxe_cq.c +++ b/drivers/infiniband/sw/rxe/rxe_cq.c @@ -62,6 +62,7 @@ int rxe_cq_from_init(struct rxe_dev *rxe, struct rxe_cq *= cq, int cqe, cq->is_user =3D uresp; =20 spin_lock_init(&cq->cq_lock); + spin_lock_init(&cq->comp_handler_lock); cq->ibcq.cqe =3D cqe; return 0; } @@ -88,6 +89,7 @@ int rxe_cq_post(struct rxe_cq *cq, struct rxe_cqe *cqe, i= nt solicited) int full; void *addr; unsigned long flags; + bool invoke_handler =3D false; =20 spin_lock_irqsave(&cq->cq_lock, flags); =20 @@ -113,11 +115,17 @@ int rxe_cq_post(struct rxe_cq *cq, struct rxe_cqe *cq= e, int solicited) if ((cq->notify & IB_CQ_NEXT_COMP) || (cq->notify & IB_CQ_SOLICITED && solicited)) { cq->notify =3D 0; - cq->ibcq.comp_handler(&cq->ibcq, cq->ibcq.cq_context); + invoke_handler =3D true; } =20 spin_unlock_irqrestore(&cq->cq_lock, flags); =20 + if (invoke_handler) { + spin_lock_irqsave(&cq->comp_handler_lock, flags); + cq->ibcq.comp_handler(&cq->ibcq, cq->ibcq.cq_context); + spin_unlock_irqrestore(&cq->comp_handler_lock, flags); + } + return 0; } =20 diff --git a/drivers/infiniband/sw/rxe/rxe_verbs.h b/drivers/infiniband/sw/= rxe/rxe_verbs.h index fd48075810dd..04ec60a786f8 100644 --- a/drivers/infiniband/sw/rxe/rxe_verbs.h +++ b/drivers/infiniband/sw/rxe/rxe_verbs.h @@ -62,6 +62,7 @@ struct rxe_cq { struct rxe_pool_elem elem; struct rxe_queue *queue; spinlock_t cq_lock; + spinlock_t comp_handler_lock; u8 notify; bool is_user; atomic_t num_wq; --=20 2.50.1