FAILED: patch "[PATCH] nvme-pci: avoid race between nvme_reap_pending_cqes() and" failed to apply to 5.6-stable tree

The patch below does not apply to the 5.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 9210c075cef29c1f764b4252f93105103bdfb292 Mon Sep 17 00:00:00 2001
From: Dongli Zhang <[email protected]>
Date: Wed, 27 May 2020 09:13:52 -0700
Subject: [PATCH] nvme-pci: avoid race between nvme_reap_pending_cqes() and
nvme_poll()

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().

index 3726dc780d15..cc46e250fcac 100644
@@ -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,