Messages in this thread | | | From | Ming Lei <> | Date | Wed, 27 May 2020 10:37:05 +0800 | Subject | Re: [PATCH 1/1] nvme-pci: avoid race between nvme_reap_pending_cqes() and nvme_poll() |
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On Wed, May 27, 2020 at 8:57 AM Dongli Zhang <dongli.zhang@oracle.com> wrote: > > 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(). > > Signed-off-by: Dongli Zhang <dongli.zhang@oracle.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); > + } > }
Looks a real race, and the fix is fine:
Reviewed-by: Ming Lei <ming.lei@redhat.com>
thanks, Ming Lei
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