Re: [PATCH] md: wake raid456 reshape waiters before suspend

[Yu Kuai]

Hi,

在 2026/4/2 10:53, Li Nan 写道:
>
>
> 在 2026/3/27 22:07, Yu Kuai 写道:
>> During raid456 reshape, direct IO across the reshape position can sleep
>> in raid5_make_request() waiting for reshape progress while still
>> holding an active_io reference. If userspace then freezes reshape and
>> writes md/suspend_lo or md/suspend_hi, mddev_suspend() kills active_io
>> and waits for all in-flight IO to drain.
>>
>> This can deadlock: the IO needs reshape progress to continue, but the
>> reshape thread is already frozen, so the active_io reference is never
>> dropped and suspend never completes.
>>
>> raid5_prepare_suspend() already wakes wait_for_reshape for dm-raid. Do
>> the same for normal md suspend when reshape is already interrupted, so
>> waiting raid456 IO can abort, drop its reference, and let suspend
>> finish.
>>
>> The mdadm test tests/25raid456-reshape-deadlock reproduces the hang.
>>
>> Fixes: 714d20150ed8 ("md: add new helpers to suspend/resume array")
>> Signed-off-by: Yu Kuai <yukuai@xxxxxxxxx>
>> ---
>>   drivers/md/md.c | 11 +++++++++++
>>   1 file changed, 11 insertions(+)
>>
>> diff --git a/drivers/md/md.c b/drivers/md/md.c
>> index 65c85973092a..3ae5f36b5baf 100644
>> --- a/drivers/md/md.c
>> +++ b/drivers/md/md.c
>> @@ -489,6 +489,17 @@ int mddev_suspend(struct mddev *mddev, bool 
>> interruptible)
>>       }
>>         percpu_ref_kill(&mddev->active_io);
>> +
>> +    /*
>> +     * RAID456 IO can sleep in wait_for_reshape while still holding an
>> +     * active_io reference. If reshape is already interrupted or 
>> frozen,
>> +     * wake those waiters so they can abort and drop the reference 
>> instead
>> +     * of deadlocking suspend.
>> +     */
>> +    if (mddev->pers && mddev->pers->prepare_suspend &&
>> +        reshape_interrupted(mddev))
>> +        mddev->pers->prepare_suspend(mddev);
>> +
>>       if (interruptible)
>>           err = wait_event_interruptible(mddev->sb_wait,
>> percpu_ref_is_zero(&mddev->active_io));
>
> If I only freeze raid5 without suspend, the IO still hangs and cannot
> complete. Should we fix this scenario?
Yes, for other path can freeze raid5 directly, we should fix it as well.
>
> -- 
> Thanks,
> Nan
>
-- 
Thansk,
Kuai