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    SubjectRe: [PATCH 3/3] nvme-pci: use queue close instead of queue freeze
    On Wed, Sep 05, 2018 at 12:09:46PM +0800, Jianchao Wang wrote:
    > nvme_dev_disable freezes queues to prevent new IO. nvme_reset_work
    > will unfreeze and wait to drain the queues. However, if IO timeout
    > at the moment, no body could do recovery as nvme_reset_work is
    > waiting. We will encounter IO hang.
    >
    > To avoid this scenario, use queue close to prevent new IO which
    > doesn't need to drain the queues. And just use queue freeze to
    > try to wait for in-flight IO for shutdown case.
    >
    > Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com>
    > ---
    > drivers/nvme/host/core.c | 22 ++++++++++++++++++++++
    > drivers/nvme/host/nvme.h | 3 +++
    > drivers/nvme/host/pci.c | 27 ++++++++++++++-------------
    > 3 files changed, 39 insertions(+), 13 deletions(-)
    >
    > diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
    > index dd8ec1d..ce5b35b 100644
    > --- a/drivers/nvme/host/core.c
    > +++ b/drivers/nvme/host/core.c
    > @@ -3602,6 +3602,28 @@ void nvme_kill_queues(struct nvme_ctrl *ctrl)
    > }
    > EXPORT_SYMBOL_GPL(nvme_kill_queues);
    >
    > +void nvme_close_queues(struct nvme_ctrl *ctrl)
    > +{
    > + struct nvme_ns *ns;
    > +
    > + down_read(&ctrl->namespaces_rwsem);
    > + list_for_each_entry(ns, &ctrl->namespaces, list)
    > + blk_set_queue_closed(ns->queue);
    > + up_read(&ctrl->namespaces_rwsem);
    > +}
    > +EXPORT_SYMBOL_GPL(nvme_close_queues);
    > +
    > +void nvme_open_queues(struct nvme_ctrl *ctrl)
    > +{
    > + struct nvme_ns *ns;
    > +
    > + down_read(&ctrl->namespaces_rwsem);
    > + list_for_each_entry(ns, &ctrl->namespaces, list)
    > + blk_clear_queue_closed(ns->queue);
    > + up_read(&ctrl->namespaces_rwsem);
    > +}
    > +EXPORT_SYMBOL_GPL(nvme_open_queues);
    > +
    > void nvme_unfreeze(struct nvme_ctrl *ctrl)
    > {
    > struct nvme_ns *ns;
    > diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
    > index bb4a200..fcd44cb 100644
    > --- a/drivers/nvme/host/nvme.h
    > +++ b/drivers/nvme/host/nvme.h
    > @@ -437,6 +437,9 @@ void nvme_wait_freeze(struct nvme_ctrl *ctrl);
    > void nvme_wait_freeze_timeout(struct nvme_ctrl *ctrl, long timeout);
    > void nvme_start_freeze(struct nvme_ctrl *ctrl);
    >
    > +void nvme_close_queues(struct nvme_ctrl *ctrl);
    > +void nvme_open_queues(struct nvme_ctrl *ctrl);
    > +
    > #define NVME_QID_ANY -1
    > struct request *nvme_alloc_request(struct request_queue *q,
    > struct nvme_command *cmd, blk_mq_req_flags_t flags, int qid);
    > diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
    > index d668682..c0ccd04 100644
    > --- a/drivers/nvme/host/pci.c
    > +++ b/drivers/nvme/host/pci.c
    > @@ -2145,23 +2145,25 @@ static void nvme_dev_disable(struct nvme_dev *dev, bool shutdown)
    > struct pci_dev *pdev = to_pci_dev(dev->dev);
    >
    > mutex_lock(&dev->shutdown_lock);
    > + nvme_close_queues(&dev->ctrl);
    > if (pci_is_enabled(pdev)) {
    > u32 csts = readl(dev->bar + NVME_REG_CSTS);
    >
    > - if (dev->ctrl.state == NVME_CTRL_LIVE ||
    > - dev->ctrl.state == NVME_CTRL_RESETTING)
    > - nvme_start_freeze(&dev->ctrl);
    > dead = !!((csts & NVME_CSTS_CFS) || !(csts & NVME_CSTS_RDY) ||
    > pdev->error_state != pci_channel_io_normal);
    > - }
    >
    > - /*
    > - * Give the controller a chance to complete all entered requests if
    > - * doing a safe shutdown.
    > - */
    > - if (!dead) {
    > - if (shutdown)
    > - nvme_wait_freeze_timeout(&dev->ctrl, NVME_IO_TIMEOUT);
    > + if (dev->ctrl.state == NVME_CTRL_LIVE ||
    > + dev->ctrl.state == NVME_CTRL_RESETTING) {
    > + /*
    > + * Give the controller a chance to complete all entered
    > + * requests if doing a safe shutdown.
    > + */
    > + if (!dead && shutdown) {
    > + nvme_start_freeze(&dev->ctrl);
    > + nvme_wait_freeze_timeout(&dev->ctrl, NVME_IO_TIMEOUT);
    > + nvme_unfreeze(&dev->ctrl);
    > + }
    > + }
    > }
    >
    > nvme_stop_queues(&dev->ctrl);
    > @@ -2328,11 +2330,9 @@ static void nvme_reset_work(struct work_struct *work)
    > new_state = NVME_CTRL_ADMIN_ONLY;
    > } else {
    > nvme_start_queues(&dev->ctrl);
    > - nvme_wait_freeze(&dev->ctrl);
    > /* hit this only when allocate tagset fails */
    > if (nvme_dev_add(dev))
    > new_state = NVME_CTRL_ADMIN_ONLY;
    > - nvme_unfreeze(&dev->ctrl);

    nvme_dev_add() still may call freeze & unfreeze queue, so your patch
    can't avoid draining queue completely here.

    Thanks,
    Ming

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