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

[Song Liu <song@kernel.org>]

On Mon, Jan 22, 2024 at 4:57 PM Dan Moulding <dan@danm.net> wrote:
>
> After upgrading from 6.7.0 to 6.7.1 a couple of my systems with md
> RAID-5 arrays started experiencing hangs. It starts with some
> processes which write to the array getting stuck. The whole system
> eventually becomes unresponsive and unclean shutdown must be performed
> (poweroff and reboot don't work).
>
> While trying to diagnose the issue, I noticed that the md0_raid5
> kernel thread consumes 100% CPU after the issue occurs. No relevant
> warnings or errors were found in dmesg.
>
> On 6.7.1, I can reproduce the issue somewhat reliably by copying a
> large amount of data to the array. I am unable to reproduce the issue
> at all on 6.7.0. The bisection was a bit difficult since I don't have
> a 100% reliable method to reproduce the problem, but with some
> perseverence I eventually managed to whittle it down to commit
> 0de40f76d567 ("Revert "md/raid5: Wait for MD_SB_CHANGE_PENDING in
> raid5d"). After reverting that commit (i.e. reapplying the reverted
> commit) on top of 6.7.1 I can no longer reproduce the problem at all.
>
> Some details that might be relevant:
> - Both systems are running MD RAID-5 with a journal device.
> - mdadm in monitor mode is always running on both systems.
> - Both systems were previously running 6.7.0 and earlier just fine.
> - The older of the two systems has been running a raid5 array without
>   incident for many years (kernel going back to at least 5.1) -- this
>   is the first raid5 issue it has encountered.
>
> Please let me know if there is any other helpful information that I
> might be able to provide.

Thanks for the report, and sorry for the problem.

We are looking into some regressions that are probably related to this.
We will fix the issue ASAP.

Song