Re: [RFC PATCH 0/4] nvme-tcp: fix hung issues for deleting
From: 许春光
Date: Wed Jun 07 2023 - 22:49:10 EST
Ming Lei <ming.lei@xxxxxxxxxx> 于2023年6月8日周四 08:56写道：
>
> On Wed, Jun 07, 2023 at 12:09:17PM +0800, 许春光 wrote:
> > Hi Ming:
> >
> > Ming Lei <ming.lei@xxxxxxxxxx> 于2023年6月6日周二 23:15写道：
> > >
> > > Hello Chunguang,
> > >
> > > On Mon, May 29, 2023 at 06:59:22PM +0800, brookxu.cn wrote:
> > > > From: Chunguang Xu <chunguang.xu@xxxxxxxxxx>
> > > >
> > > > We found that nvme_remove_namespaces() may hang in flush_work(&ctrl->scan_work)
> > > > while removing ctrl. The root cause may due to the state of ctrl changed to
> > > > NVME_CTRL_DELETING while removing ctrl , which intterupt nvme_tcp_error_recovery_work()/
> > > > nvme_reset_ctrl_work()/nvme_tcp_reconnect_or_remove(). At this time, ctrl is
> > >
> > > I didn't dig into ctrl state check in these error handler yet, but error
> > > handling is supposed to provide forward progress for any controller state.
> > >
> > > Can you explain a bit how switching to DELETING interrupts the above
> > > error handling and breaks the forward progress guarantee?
> >
> > Here we freezed ctrl, if ctrl state has changed to DELETING or
> > DELETING_NIO(by nvme disconnect), we will break up and lease ctrl
> > freeze, so nvme_remove_namespaces() hang.
> >
> > static void nvme_tcp_error_recovery_work(struct work_struct *work)
> > {
> > ...
> > if (!nvme_change_ctrl_state(ctrl, NVME_CTRL_CONNECTING)) {
> > /* state change failure is ok if we started ctrl delete */
> > WARN_ON_ONCE(ctrl->state != NVME_CTRL_DELETING &&
> > ctrl->state != NVME_CTRL_DELETING_NOIO);
> > return;
> > }
> >
> > nvme_tcp_reconnect_or_remove(ctrl);
> > }
> >
> >
> > Another path, we will check ctrl state while reconnecting, if it changes to
> > DELETING or DELETING_NIO, we will break up and lease ctrl freeze and
> > queue quiescing (through reset path), as a result Hang occurs.
> >
> > static void nvme_tcp_reconnect_or_remove(struct nvme_ctrl *ctrl)
> > {
> > /* If we are resetting/deleting then do nothing */
> > if (ctrl->state != NVME_CTRL_CONNECTING) {
> > WARN_ON_ONCE(ctrl->state == NVME_CTRL_NEW ||
> > ctrl->state == NVME_CTRL_LIVE);
> > return;
> > }
> > ...
> > }
> >
> > > > freezed and queue is quiescing . Since scan_work may continue to issue IOs to
> > > > load partition table, make it blocked, and lead to nvme_tcp_error_recovery_work()
> > > > hang in flush_work(&ctrl->scan_work).
> > > >
> > > > After analyzation, we found that there are mainly two case:
> > > > 1. Since ctrl is freeze, scan_work hang in __bio_queue_enter() while it issue
> > > > new IO to load partition table.
> > >
> > > Yeah, nvme freeze usage is fragile, and I suggested to move
> > > nvme_start_freeze() from nvme_tcp_teardown_io_queues to
> > > nvme_tcp_configure_io_queues(), such as the posted change on rdma:
> > >
> > > https://lore.kernel.org/linux-block/CAHj4cs-4gQHnp5aiekvJmb6o8qAcb6nLV61uOGFiisCzM49_dg@xxxxxxxxxxxxxx/T/#ma0d6bbfaa0c8c1be79738ff86a2fdcf7582e06b0
> >
> > While drive reconnecting, I think we should freeze ctrl or quiescing queue,
> > otherwise nvme_fail_nonready_command()may return BLK_STS_RESOURCE,
> > and the IOs may retry frequently. So I think we may better freeze ctrl
> > while entering
> > error_recovery/reconnect, but need to unfreeze it while exit.
>
> quiescing is always done in error handling, and freeze is actually
> not a must, and it is easier to cause race by calling freeze & unfreeze
> from different contexts.
I think if we donot freeze ctrl, as the IO already submit (just queue
to hctx->dispatch) and may
pending for a long time, it may trigger new hang task issue, but
freeze ctrl may can avoid these
hang task.
> But yes, unquiesce should have been done after exiting error handling, or
> simply do it in nvme_unquiesce_io_queues().
>
> And the following patch should cover all these hangs:
>
>
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 3ec38e2b9173..83d3818fc60b 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -4692,6 +4692,9 @@ void nvme_remove_namespaces(struct nvme_ctrl *ctrl)
> */
> nvme_mpath_clear_ctrl_paths(ctrl);
>
> + /* unquiesce io queues so scan work won't hang */
> + nvme_unquiesce_io_queues(ctrl);
> +
> /* prevent racing with ns scanning */
> flush_work(&ctrl->scan_work);
>
> @@ -4701,10 +4704,8 @@ void nvme_remove_namespaces(struct nvme_ctrl *ctrl)
> * removing the namespaces' disks; fail all the queues now to avoid
> * potentially having to clean up the failed sync later.
> */
> - if (ctrl->state == NVME_CTRL_DEAD) {
> + if (ctrl->state == NVME_CTRL_DEAD)
> nvme_mark_namespaces_dead(ctrl);
> - nvme_unquiesce_io_queues(ctrl);
> - }
>
> /* this is a no-op when called from the controller reset handler */
> nvme_change_ctrl_state(ctrl, NVME_CTRL_DELETING_NOIO);
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index 492f319ebdf3..5d775b76baca 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -2578,14 +2578,15 @@ static void nvme_dev_disable(struct nvme_dev *dev, bool shutdown)
> dead = nvme_pci_ctrl_is_dead(dev);
> if (dev->ctrl.state == NVME_CTRL_LIVE ||
> dev->ctrl.state == NVME_CTRL_RESETTING) {
> - if (pci_is_enabled(pdev))
> - nvme_start_freeze(&dev->ctrl);
> /*
> * Give the controller a chance to complete all entered requests
> * if doing a safe shutdown.
> */
> - if (!dead && shutdown)
> + if (!dead && shutdown & pci_is_enabled(pdev)) {
> + nvme_start_freeze(&dev->ctrl);
> nvme_wait_freeze_timeout(&dev->ctrl, NVME_IO_TIMEOUT);
> + nvme_unfreeze(&dev->ctrl);
> + }
> }
>
> nvme_quiesce_io_queues(&dev->ctrl);
> @@ -2740,6 +2741,7 @@ static void nvme_reset_work(struct work_struct *work)
> * controller around but remove all namespaces.
> */
> if (dev->online_queues > 1) {
> + nvme_start_freeze(&dev->ctrl);
> nvme_unquiesce_io_queues(&dev->ctrl);
> nvme_wait_freeze(&dev->ctrl);
> nvme_pci_update_nr_queues(dev);
> diff --git a/drivers/nvme/host/rdma.c b/drivers/nvme/host/rdma.c
> index 0eb79696fb73..354cce8853c1 100644
> --- a/drivers/nvme/host/rdma.c
> +++ b/drivers/nvme/host/rdma.c
> @@ -918,6 +918,7 @@ static int nvme_rdma_configure_io_queues(struct nvme_rdma_ctrl *ctrl, bool new)
> goto out_cleanup_tagset;
>
> if (!new) {
> + nvme_start_freeze(&ctrl->ctrl);
> nvme_unquiesce_io_queues(&ctrl->ctrl);
> if (!nvme_wait_freeze_timeout(&ctrl->ctrl, NVME_IO_TIMEOUT)) {
> /*
> @@ -926,6 +927,7 @@ static int nvme_rdma_configure_io_queues(struct nvme_rdma_ctrl *ctrl, bool new)
> * to be safe.
> */
> ret = -ENODEV;
> + nvme_unfreeze(&ctrl->ctrl);
> goto out_wait_freeze_timed_out;
> }
> blk_mq_update_nr_hw_queues(ctrl->ctrl.tagset,
> @@ -975,7 +977,6 @@ static void nvme_rdma_teardown_io_queues(struct nvme_rdma_ctrl *ctrl,
> bool remove)
> {
> if (ctrl->ctrl.queue_count > 1) {
> - nvme_start_freeze(&ctrl->ctrl);
> nvme_quiesce_io_queues(&ctrl->ctrl);
> nvme_sync_io_queues(&ctrl->ctrl);
> nvme_rdma_stop_io_queues(ctrl);
> diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
> index bf0230442d57..5ae08e9cb16d 100644
> --- a/drivers/nvme/host/tcp.c
> +++ b/drivers/nvme/host/tcp.c
> @@ -1909,6 +1909,7 @@ static int nvme_tcp_configure_io_queues(struct nvme_ctrl *ctrl, bool new)
> goto out_cleanup_connect_q;
>
> if (!new) {
> + nvme_start_freeze(ctrl);
> nvme_unquiesce_io_queues(ctrl);
> if (!nvme_wait_freeze_timeout(ctrl, NVME_IO_TIMEOUT)) {
> /*
> @@ -1917,6 +1918,7 @@ static int nvme_tcp_configure_io_queues(struct nvme_ctrl *ctrl, bool new)
> * to be safe.
> */
> ret = -ENODEV;
> + nvme_unfreeze(ctrl);
> goto out_wait_freeze_timed_out;
> }
> blk_mq_update_nr_hw_queues(ctrl->tagset,
> @@ -2021,7 +2023,6 @@ static void nvme_tcp_teardown_io_queues(struct nvme_ctrl *ctrl,
> if (ctrl->queue_count <= 1)
> return;
> nvme_quiesce_admin_queue(ctrl);
> - nvme_start_freeze(ctrl);
> nvme_quiesce_io_queues(ctrl);
> nvme_sync_io_queues(ctrl);
> nvme_tcp_stop_io_queues(ctrl);
>
>
>
>
> Thanks
> Ming
>