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Wed, 28 Oct 2026 23:49:33 +0000 (UTC) From: Bart Van Assche To: Jens Axboe , Josef Bacik , Chris Mason Cc: Justin Sanders , linux-block@vger.kernel.org, Christoph Hellwig , Sagi Grimberg , Chaitanya Kulkarni Subject: Re: [PATCH 90/98] nvmet-rdma: disable interrupts under rsp_wr_wait_lock Date: Wed, 28 Oct 2026 16:49:13 -0700 Message-ID: <20261028234917.3067347-8-bvanassche@acm.org> X-Mailer: git-send-email 2.56.0.313.g2479322e68-goog In-Reply-To: <20261028164415.1262013-91-axboe@kernel.dk> References: <20261028164415.1262013-1-axboe@kernel.dk> <20261028164415.1262013-91-axboe@kernel.dk> X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable On 10/28/26 09:42, Jens Axboe wrote: > - spin_unlock(&queue->rsp_wr_wait_lock); > + spin_unlock_irqrestore(&queue->rsp_wr_wait_lock, flags); > ret =3D nvmet_rdma_execute_command(rsp); > - spin_lock(&queue->rsp_wr_wait_lock); > + spin_lock_irqsave(&queue->rsp_wr_wait_lock, flags); Using spin_lock_irqsave() fixes the rsp_wr_wait_lock deadlock itself, but when nvmet_rdma_process_wr_wait_list() is reached from a bio end_io callback in hardirq or softirq context (via nvmet_req_complete() -> nvmet_rdma_queue_response() -> failed ib_post_send() -> nvmet_rdma_release_rsp()), spin_unlock_irqrestore() restores that hardirq/softirq context and calls nvmet_rdma_execute_command(rsp) -> rsp->req.execute(&rsp->req). The nvmet ->execute() handlers require process context: - nvmet_bdev_execute_rw() allocates bios with GFP_KERNEL and calls submit_bio() -> submit_bio_noacct(), which hits might_sleep() and manipulates current->bio_list without interrupt synchronization. - Admin, fabrics, auth, and PR handlers perform GFP_KERNEL allocations and take mutexes / rwsems. If nvmet_rdma_process_wr_wait_list() checks !in_task() under rsp_wr_wait_lock and schedules a per-queue wr_wait_work on system_dfl_wq when rsp_wr_wait_list is non-empty (cancelled after ib_drain_qp() in nvmet_rdma_destroy_queue_ib()), normal task/CQ-workqueue callers pay no extra cost while hardirq/softirq completions safely defer command execution to process context. Note: patches 91/98 and 92/98 compose cleanly on top by placing the if (done && done->wait_released) check right above if (!in_task()) and passing NULL from nvmet_rdma_wr_wait_work(). Here is a replacement patch (checked with checkpatch.pl and syntax-checked with Clang; not runtime-tested): --- diff --git a/drivers/nvme/target/rdma.c b/drivers/nvme/target/rdma.c index 26ea4e1d62b3..60ea488db8f4 100644 --- a/drivers/nvme/target/rdma.c +++ b/drivers/nvme/target/rdma.c @@ -104,6 +104,7 @@ struct nvmet_rdma_queue { struct nvmet_rdma_cmd *cmds; =20 struct work_struct release_work; + struct work_struct wr_wait_work; struct list_head rsp_wait_list; struct list_head rsp_wr_wait_list; spinlock_t rsp_wr_wait_lock; @@ -513,7 +514,15 @@ static int nvmet_rdma_post_recv(struct nvmet_rdma_de= vice *ndev, =20 static void nvmet_rdma_process_wr_wait_list(struct nvmet_rdma_queue *que= ue) { - spin_lock(&queue->rsp_wr_wait_lock); + unsigned long flags; + + spin_lock_irqsave(&queue->rsp_wr_wait_lock, flags); + if (!in_task()) { + if (!list_empty(&queue->rsp_wr_wait_list)) + schedule_work(&queue->wr_wait_work); + spin_unlock_irqrestore(&queue->rsp_wr_wait_lock, flags); + return; + } while (!list_empty(&queue->rsp_wr_wait_list)) { struct nvmet_rdma_rsp *rsp; bool ret; @@ -522,16 +531,24 @@ static void nvmet_rdma_process_wr_wait_list(struct = nvmet_rdma_queue *queue) struct nvmet_rdma_rsp, wait_list); list_del(&rsp->wait_list); =20 - spin_unlock(&queue->rsp_wr_wait_lock); + spin_unlock_irqrestore(&queue->rsp_wr_wait_lock, flags); ret =3D nvmet_rdma_execute_command(rsp); - spin_lock(&queue->rsp_wr_wait_lock); + spin_lock_irqsave(&queue->rsp_wr_wait_lock, flags); =20 if (!ret) { list_add(&rsp->wait_list, &queue->rsp_wr_wait_list); break; } } - spin_unlock(&queue->rsp_wr_wait_lock); + spin_unlock_irqrestore(&queue->rsp_wr_wait_lock, flags); +} + +static void nvmet_rdma_wr_wait_work(struct work_struct *w) +{ + struct nvmet_rdma_queue *queue =3D + container_of(w, struct nvmet_rdma_queue, wr_wait_work); + + nvmet_rdma_process_wr_wait_list(queue); } =20 static u16 nvmet_rdma_check_pi_status(struct ib_mr *sig_mr) @@ -976,6 +993,7 @@ static bool nvmet_rdma_execute_command(struct nvmet_r= dma_rsp *rsp) static void nvmet_rdma_handle_command(struct nvmet_rdma_queue *queue, struct nvmet_rdma_rsp *cmd) { + unsigned long flags; u16 status; =20 ib_dma_sync_single_for_cpu(queue->dev->device, @@ -993,9 +1011,9 @@ static void nvmet_rdma_handle_command(struct nvmet_r= dma_queue *queue, goto out_err; =20 if (unlikely(!nvmet_rdma_execute_command(cmd))) { - spin_lock(&queue->rsp_wr_wait_lock); + spin_lock_irqsave(&queue->rsp_wr_wait_lock, flags); list_add_tail(&cmd->wait_list, &queue->rsp_wr_wait_list); - spin_unlock(&queue->rsp_wr_wait_lock); + spin_unlock_irqrestore(&queue->rsp_wr_wait_lock, flags); } =20 return; @@ -1374,6 +1392,7 @@ static bool nvmet_rdma_reclaim_rsp(struct sbitmap *= sb, unsigned int bitnr, static void nvmet_rdma_destroy_queue_ib(struct nvmet_rdma_queue *queue) { ib_drain_qp(queue->qp); + cancel_work_sync(&queue->wr_wait_work); =20 /* * Reclaim resources of a response that is still in-flight when the @@ -1494,6 +1513,7 @@ nvmet_rdma_alloc_queue(struct nvmet_rdma_device *nd= ev, * inside a CM callback would trigger a deadlock. (great API design..) */ INIT_WORK(&queue->release_work, nvmet_rdma_release_queue_work); + INIT_WORK(&queue->wr_wait_work, nvmet_rdma_wr_wait_work); queue->dev =3D ndev; queue->cm_id =3D cm_id; queue->port =3D port->nport;