Re: [PATCH v2 1/1] nvme/mpath: fix hang when disk goes live over reconnect

[Sagi Grimberg <sagi@grimberg.me>]

On 3/23/22 05:55, Anton Eidelman wrote:
> nvme_mpath_init_identify() invoked from nvme_init_identify()
> fetches a fresh ANA log from the ctrl.
> This is essential to have an up to date path states
> for both existing namespaces and for those scan_work
> may discover once the ctrl is up.
> 
> This happens in the following cases:
> 1) A new ctrl is being connected.
> 2) An existing ctrl is successfully reconnected.
> 3) An existing ctrl is being reset.
> 
> While in (1) ctrl->namespaces is empty, (2 & 3) may have namespaces,
> and nvme_read_ana_log() may call nvme_update_ns_ana_state().
> 
> This result in a hang when the ANA state of an existing namespace
> changes and makes the disk live: nvme_mpath_set_live() issues
> IO to the namespace through the ctrl,
> which does NOT have IO queues yet.

Given that setting the path as live triggers I/O, it makes perfect
sense to do it only after we have I/O queues that can accept this
I/O.

> 
> See sample hang below.
> 
> Solution:
> - nvme_update_ns_ana_state() to call set_live only if ctrl is live
> - nvme_read_ana_log() call from nvme_mpath_init_identify()
>    therefore only fetches and parses the ANA log;
>    any erros in this process will fail the ctrl setup as appropriate;
> - a separate function nvme_mpath_update()
>    is called in nvme_start_ctrl();
>    this parses the ANA log without fetching it.
>    At this point the ctrl is live,
>    therefore, disks can be set live normally.
> 
> Sample failure:
>      nvme nvme0: starting error recovery
>      nvme nvme0: Reconnecting in 10 seconds...
>      block nvme0n6: no usable path - requeuing I/O
>      INFO: task kworker/u8:3:312 blocked for more than 122 seconds.
>            Tainted: G            E     5.14.5-1.el7.elrepo.x86_64 #1
>      Workqueue: nvme-wq nvme_tcp_reconnect_ctrl_work [nvme_tcp]
>      Call Trace:
>       __schedule+0x2a2/0x7e0
>       schedule+0x4e/0xb0
>       io_schedule+0x16/0x40
>       wait_on_page_bit_common+0x15c/0x3e0
>       do_read_cache_page+0x1e0/0x410
>       read_cache_page+0x12/0x20
>       read_part_sector+0x46/0x100
>       read_lba+0x121/0x240
>       efi_partition+0x1d2/0x6a0
>       bdev_disk_changed.part.0+0x1df/0x430
>       bdev_disk_changed+0x18/0x20
>       blkdev_get_whole+0x77/0xe0
>       blkdev_get_by_dev+0xd2/0x3a0
>       __device_add_disk+0x1ed/0x310
>       device_add_disk+0x13/0x20
>       nvme_mpath_set_live+0x138/0x1b0 [nvme_core]
>       nvme_update_ns_ana_state+0x2b/0x30 [nvme_core]
>       nvme_update_ana_state+0xca/0xe0 [nvme_core]
>       nvme_parse_ana_log+0xac/0x170 [nvme_core]
>       nvme_read_ana_log+0x7d/0xe0 [nvme_core]
>       nvme_mpath_init_identify+0x105/0x150 [nvme_core]
>       nvme_init_identify+0x2df/0x4d0 [nvme_core]
>       nvme_init_ctrl_finish+0x8d/0x3b0 [nvme_core]
>       nvme_tcp_setup_ctrl+0x337/0x390 [nvme_tcp]
>       nvme_tcp_reconnect_ctrl_work+0x24/0x40 [nvme_tcp]
>       process_one_work+0x1bd/0x360
>       worker_thread+0x50/0x3d0
> 
> Signed-off-by: Anton Eidelman <anton@lightbitslabs.com>
> ---
>   drivers/nvme/host/core.c      |  1 +
>   drivers/nvme/host/multipath.c | 12 +++++++++++-
>   drivers/nvme/host/nvme.h      |  4 ++++
>   3 files changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 3c0461129bca..d4495fa97657 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -4509,6 +4509,7 @@ void nvme_start_ctrl(struct nvme_ctrl *ctrl)
>   	if (ctrl->queue_count > 1) {
>   		nvme_queue_scan(ctrl);
>   		nvme_start_queues(ctrl);
> +		nvme_mpath_update(ctrl);
>   	}
>   
>   	nvme_change_uevent(ctrl, "NVME_EVENT=connected");
> diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
> index c97d7f843977..a22d455f48a9 100644
> --- a/drivers/nvme/host/multipath.c
> +++ b/drivers/nvme/host/multipath.c
> @@ -613,7 +613,8 @@ static void nvme_update_ns_ana_state(struct nvme_ana_group_desc *desc,
>   	ns->ana_state = desc->state;
>   	clear_bit(NVME_NS_ANA_PENDING, &ns->flags);
>   

I think we need a comment here explaining this. something like:

	/*
	 * nvme_mpath_set_live() will trigger I/O to the mpath
	 * device node and in turn to this path device, however we
	 * cannot accept this I/O if the ctrl is not live, this may
	 * deadlock if called from the nvme_mpath_init_identify and
	 * the controller will never complete initialization, preventing
	 * I/O from completing. For this we will reprocess the ANA log
	 * page again once the controller will be fully initialized.
	 */

> -	if (nvme_state_is_live(ns->ana_state))
> +	if (nvme_state_is_live(ns->ana_state) &&
> +		(ns->ctrl->state == NVME_CTRL_LIVE))

No need for the brackets I think, and

Alignment should be:
	if (nvme_state_is_live(ns->ana_state) &&
	    ns->ctrl->state == NVME_CTRL_LIVE)

>   		nvme_mpath_set_live(ns);
>   }
>   
> @@ -700,6 +701,15 @@ static void nvme_ana_work(struct work_struct *work)
>   	nvme_read_ana_log(ctrl);
>   }
>   
> +void nvme_mpath_update(struct nvme_ctrl *ctrl)
> +{
> +	u32 nr_change_groups = 0;
> +
> +	mutex_lock(&ctrl->ana_lock);
> +	nvme_parse_ana_log(ctrl, &nr_change_groups, nvme_update_ana_state);
> +	mutex_unlock(&ctrl->ana_lock);
> +}
> +
>   static void nvme_anatt_timeout(struct timer_list *t)
>   {
>   	struct nvme_ctrl *ctrl = from_timer(ctrl, t, anatt_timer);
> diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
> index 1ea908d43e17..76f7a5f37379 100644
> --- a/drivers/nvme/host/nvme.h
> +++ b/drivers/nvme/host/nvme.h
> @@ -781,6 +781,7 @@ void nvme_mpath_add_disk(struct nvme_ns *ns, struct nvme_id_ns *id);
>   void nvme_mpath_remove_disk(struct nvme_ns_head *head);
>   int nvme_mpath_init_identify(struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id);
>   void nvme_mpath_init_ctrl(struct nvme_ctrl *ctrl);
> +void nvme_mpath_update(struct nvme_ctrl *ctrl);
>   void nvme_mpath_uninit(struct nvme_ctrl *ctrl);
>   void nvme_mpath_stop(struct nvme_ctrl *ctrl);
>   bool nvme_mpath_clear_current_path(struct nvme_ns *ns);
> @@ -852,6 +853,9 @@ static inline int nvme_mpath_init_identify(struct nvme_ctrl *ctrl,
>   "Please enable CONFIG_NVME_MULTIPATH for full support of multi-port devices.\n");
>   	return 0;
>   }
> +void nvme_mpath_update(struct nvme_ctrl *ctrl)
> +{
> +}
>   static inline void nvme_mpath_uninit(struct nvme_ctrl *ctrl)
>   {
>   }