[PATCH 3/3] nvme-multipath: stuck partition scan on inaccessible paths

[Sagi Grimberg]

On 11/09/2024 15:46, Hannes Reinecke wrote:
> When a path is switched to 'inaccessible' during partition scan
> triggered via device_add_disk() and we only have one path the
> system will be stuck as nvme_available_path() will always return
> 'true'. So I/O will never be completed and the system is stuck
> in device_add_disk():
>
>      [<0>] folio_wait_bit_common+0x12a/0x310
>      [<0>] filemap_read_folio+0x97/0xd0
>      [<0>] do_read_cache_folio+0x108/0x390
>      [<0>] read_part_sector+0x31/0xa0
>      [<0>] read_lba+0xc5/0x160
>      [<0>] efi_partition+0xd9/0x8f0
>      [<0>] bdev_disk_changed+0x23d/0x6d0
>      [<0>] blkdev_get_whole+0x78/0xc0
>      [<0>] bdev_open+0x2c6/0x3b0
>      [<0>] bdev_file_open_by_dev+0xcb/0x120
>      [<0>] disk_scan_partitions+0x5d/0x100
>      [<0>] device_add_disk+0x402/0x420
>      [<0>] nvme_mpath_set_live+0x4f/0x1f0 [nvme_core]
>      [<0>] nvme_mpath_add_disk+0x107/0x120 [nvme_core]
>      [<0>] nvme_alloc_ns+0xac6/0xe60 [nvme_core]
>      [<0>] nvme_scan_ns+0x2dd/0x3e0 [nvme_core]
>      [<0>] nvme_scan_work+0x1a3/0x490 [nvme_core]
>
> This patch introduces a flag NVME_NSHEAD_FAIL_ON_LAST_PATH to
> cause nvme_available_path() to always return NULL, and with
> that I/O to be failed if the last path is unavailable. But
> we also need to requeue all pending I/Os whenever we have
> changed the ANA state as now even inaccessible ANA states
> influence I/O behaviour.
>
> Signed-off-by: Hannes Reinecke <hare at kernel.org>
> ---
>   drivers/nvme/host/multipath.c | 15 +++++++++++++++
>   drivers/nvme/host/nvme.h      |  1 +
>   2 files changed, 16 insertions(+)
>
> diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
> index f72c5a6a2d8e..0373b4043eea 100644
> --- a/drivers/nvme/host/multipath.c
> +++ b/drivers/nvme/host/multipath.c
> @@ -422,6 +422,10 @@ static bool nvme_available_path(struct nvme_ns_head *head)
>   	struct nvme_ns *ns;
>   
>   	if (!test_bit(NVME_NSHEAD_DISK_LIVE, &head->flags))
> +	    return NULL;
> +
> +	if (test_bit(NVME_NSHEAD_FAIL_ON_LAST_PATH, &head->flags) &&
> +	    list_is_singular(&head->list))
>   		return NULL;

This is wrong too Hannes.

If you added a live path, and when partition scan triggers your path becomes
inaccessible, but then after anatt it becomes optimized again. You just 
ended
up without discovering partitions...