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 stable@vger.kernel.org.

thanks,

greg k-h

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

From 9210c075cef29c1f764b4252f93105103bdfb292 Mon Sep 17 00:00:00 2001

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()

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

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,