[PATCH 3/3] nvme: 'nvme disconnect' hangs after remapping namespaces

[Sagi Grimberg]

On 06/09/2024 13:16, Hannes Reinecke wrote:
> During repetitive namespace map and unmap operations on the target
> (disabling the namespace, changing the UUID, enabling it again)
> the initial scan will hang as the target will be returning
> PATH_ERROR and the I/O is constantly retried:
>
> [<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]
>
> Calling 'nvme disconnect' on controllers with these namespaces
> will hang as the disconnect operation tries to flush scan_work:
>
> [<0>] __flush_work+0x389/0x4b0
> [<0>] nvme_remove_namespaces+0x4b/0x130 [nvme_core]
> [<0>] nvme_do_delete_ctrl+0x72/0x90 [nvme_core]
> [<0>] nvme_delete_ctrl_sync+0x2e/0x40 [nvme_core]
> [<0>] nvme_sysfs_delete+0x35/0x40 [nvme_core]
> [<0>] kernfs_fop_write_iter+0x13d/0x1b0
> [<0>] vfs_write+0x404/0x510
>
> before the namespaces are removed.
>
> This patch sets the 'failfast_expired' bit for the controller
> to cause all pending I/O to be failed, and the disconnect process
> to complete.

I don't know if I agree with this approach. Seems too indirect.
Can you please explain (with tracing) what is preventing the scan_work
to complete? because the controller state should be DELETING, and perhaps
we are missing somewhere a check for this?

nvme_remove_namespaces() at the point you are injecting here is designed
to allow any writeback to complete (if possible).