From: Dongli Zhang <dongli.zhang@oracle.com>

Date: Wed, 27 May 2020 09:13:52 -0700

Subject: [PATCH] nvme-pci: avoid race between nvme_reap_pending_cqes() and

 nvme_poll()

Git-commit: 9210c075cef29c1f764b4252f93105103bdfb292

Patch-mainline: v5.7

References: git-fixes

There may be a race between nvme_reap_pending_cqes() and nvme_poll(), e.g.,

when doing live reset while polling the nvme device.

      CPU X                        CPU Y

                               nvme_poll()

nvme_dev_disable()

-> nvme_stop_queues()

-> nvme_suspend_io_queues()

-> nvme_suspend_queue()

                               -> spin_lock(&nvmeq->cq_poll_lock);

-> nvme_reap_pending_cqes()

   -> nvme_process_cq()        -> nvme_process_cq()

In the above scenario, the nvme_process_cq() for the same queue may be

running on both CPU X and CPU Y concurrently.

It is much more easier to reproduce the issue when CONFIG_PREEMPT is

enabled in kernel. When CONFIG_PREEMPT is disabled, it would take longer

time for nvme_stop_queues()-->blk_mq_quiesce_queue() to wait for grace

period.

This patch protects nvme_process_cq() with nvmeq->cq_poll_lock in

nvme_reap_pending_cqes().

Fixes: fa46c6fb5d61 ("nvme/pci: move cqe check after device shutdown")

Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>

Reviewed-by: Ming Lei <ming.lei@redhat.com>

Reviewed-by: Keith Busch <kbusch@kernel.org>

Signed-off-by: Christoph Hellwig <hch@lst.de>

Acked-by: Hannes Reinecke <hare@suse.com>

---

 drivers/nvme/host/pci.c | 11 +++++++----

 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c

index 3726dc780d15..cc46e250fcac 100644

--- a/drivers/nvme/host/pci.c

+++ b/drivers/nvme/host/pci.c

@@ -1382,16 +1382,19 @@ static void nvme_disable_admin_queue(struct nvme_dev *dev, bool shutdown)

 /*

  * Called only on a device that has been disabled and after all other threads

- * that can check this device's completion queues have synced. This is the

- * last chance for the driver to see a natural completion before

- * nvme_cancel_request() terminates all incomplete requests.

+ * that can check this device's completion queues have synced, except

+ * nvme_poll(). This is the last chance for the driver to see a natural

+ * completion before nvme_cancel_request() terminates all incomplete requests.

  */

 static void nvme_reap_pending_cqes(struct nvme_dev *dev)

 {

 	int i;

-	for (i = dev->ctrl.queue_count - 1; i > 0; i--)

+	for (i = dev->ctrl.queue_count - 1; i > 0; i--) {

+		spin_lock(&dev->queues[i].cq_poll_lock);

 		nvme_process_cq(&dev->queues[i]);

+		spin_unlock(&dev->queues[i].cq_poll_lock);

+	}

 }

 static int nvme_cmb_qdepth(struct nvme_dev *dev, int nr_io_queues,

-- 

2.29.2