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Date: Sun, 11 Jun 2023 11:11:06 +0300
From: Sagi Grimberg <sagi@...mberg.me>
To: Ming Lei <ming.lei@...hat.com>,
许春光 <brookxu.cn@...il.com>
Cc: kbusch@...nel.org, axboe@...nel.dk, hch@....de,
linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/4] nvme-tcp: fix hung issues for deleting
>> Hi Ming:
>>
>> Ming Lei <ming.lei@...hat.com> 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@...pee.com>
>>>>
>>>> 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@mail.gmail.com/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.
>
> 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:
>
Ming, are you sending a formal patchset for this?
>
> 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);
What guarantees that the queues won't be quiesced right after this
by the transport?
I'm still unclear why this affects the scan_work?
> +
> /* 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
>
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