Re: [REGRESSION] 6.7.1: md: raid5 hang and unresponsive system; successfully bisected

[Song Liu <song@kernel.org>]

Update my findings so far.

On Tue, Jan 30, 2024 at 8:27 AM Blazej Kucman
<blazej.kucman@linux.intel.com> wrote:
[...]
> Our daily tests directed at mdadm/md also detected a problem with
> identical symptoms as described in the thread.
>
> Issue detected with IMSM metadata but it also reproduces with native
> metadata.
> NVMe disks under VMD controller were used.
>
> Scenario:
> 1. Create raid10:
> mdadm --create /dev/md/r10d4s128-15_A --level=10 --chunk=128
> --raid-devices=4 /dev/nvme6n1 /dev/nvme2n1 /dev/nvme3n1 /dev/nvme0n1
> --size=7864320 --run
> 2. Create FS
> mkfs.ext4 /dev/md/r10d4s128-15_A
> 3. Set faulty one raid member:
> mdadm --set-faulty /dev/md/r10d4s128-15_A /dev/nvme3n1

With a failed drive, md_thread calls md_check_recovery() and kicks
off mddev->sync_work, which is md_start_sync().
md_check_recovery() also sets MD_RECOVERY_RUNNING.

md_start_sync() calls mddev_suspend() and waits for
mddev->active_io to become zero.

> 4. Stop raid devies:
> mdadm -Ss

This command calls stop_sync_thread() and waits for
MD_RECOVERY_RUNNING to be cleared.

Given we need a working file system to reproduce the issue, I
suspect the problem comes from active_io.

Yu Kuai, I guess we missed this case in the recent refactoring.
I don't have a good idea to fix this. Please also take a look into
this.

Thanks,
Song