linux-kernel - Re: [PATCH v2 05/11] md: export helpers to stop sync

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Date: Fri, 26 Jan 2024 10:38:11 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Yu Kuai <yukuai1@...weicloud.com>, Xiao Ni <xni@...hat.com>
Cc: agk@...hat.com, snitzer@...nel.org, mpatocka@...hat.com,
 dm-devel@...ts.linux.dev, song@...nel.org, jbrassow@....redhat.com,
 neilb@...e.de, heinzm@...hat.com, shli@...com, akpm@...l.org,
 linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
 yi.zhang@...wei.com, yangerkun@...wei.com,
 "yukuai3 >> yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH v2 05/11] md: export helpers to stop sync_thread

Hi,

在 2024/01/25 15:57, Yu Kuai 写道:
> Hi,
> 
> 在 2024/01/25 15:51, Xiao Ni 写道:
>> On Wed, Jan 24, 2024 at 5:19 PM Yu Kuai <yukuai3@...wei.com> wrote:
>>>
>>> The new heleprs will be used in dm-raid in later patches to fix
>>> regressions and prevent calling md_reap_sync_thread() directly.
>>>
>>> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
>>> ---
>>>   drivers/md/md.c | 41 +++++++++++++++++++++++++++++++++++++----
>>>   drivers/md/md.h |  3 +++
>>>   2 files changed, 40 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/md/md.c b/drivers/md/md.c
>>> index 6c5d0a372927..90cf31b53804 100644
>>> --- a/drivers/md/md.c
>>> +++ b/drivers/md/md.c
>>> @@ -4915,30 +4915,63 @@ static void stop_sync_thread(struct mddev 
>>> *mddev, bool locked, bool check_seq)
>>>                  mddev_lock_nointr(mddev);
>>>   }
>>>
>>> -static void idle_sync_thread(struct mddev *mddev)
>>> +void md_idle_sync_thread(struct mddev *mddev)
>>>   {
>>> +       lockdep_assert_held(mddev->reconfig_mutex);
>>> +
>>
>> Hi Kuai
>>
>> There is a building error. It should give a pointer to
>> lockdep_assert_held. And same with the other two places in this patch.
> 
> Yes, I forgot that I disabled all the debug config in order to let tests
> finish quickly.

I enabled these debuging conifg, and turns out this patch has some
problem, see below.
> 
> Thanks for the notince, will fix this in v3.
> 
> Thanks,
> Kuai
> 
>>
>> Regards
>> Xiao
>>
>>>          mutex_lock(&mddev->sync_mutex);
>>>          clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
>>> +       stop_sync_thread(mddev, true, true);
>>> +       mutex_unlock(&mddev->sync_mutex);
>>> +}
>>> +EXPORT_SYMBOL_GPL(md_idle_sync_thread);
>>> +
>>> +void md_frozen_sync_thread(struct mddev *mddev)
>>> +{
>>> +       lockdep_assert_held(mddev->reconfig_mutex);
>>> +
>>> +       mutex_lock(&mddev->sync_mutex);
>>> +       set_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
>>> +       stop_sync_thread(mddev, true, false);

stop_sync_thread() may release 'reconfig_mutex' and grab it again, hence
it's not right to grab 'sync_mutex' before 'reconfig_mutex'.

Since 'sync_mutex' is introduced to serialize sysfs api 'sync_action'
writers, while is not involved for dm-raid. I'll remove 'sync_mutex' for
the new helper in v3.

Thanks,
Kuai

>>> +       mutex_unlock(&mddev->sync_mutex);
>>> +}
>>> +EXPORT_SYMBOL_GPL(md_frozen_sync_thread);
>>>
>>> +void md_unfrozen_sync_thread(struct mddev *mddev)
>>> +{
>>> +       lockdep_assert_held(mddev->reconfig_mutex);
>>> +
>>> +       mutex_lock(&mddev->sync_mutex);
>>> +       clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
>>> +       set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
>>> +       md_wakeup_thread(mddev->thread);
>>> +       sysfs_notify_dirent_safe(mddev->sysfs_action);
>>> +       mutex_unlock(&mddev->sync_mutex);
>>> +}
>>> +EXPORT_SYMBOL_GPL(md_unfrozen_sync_thread);
>>> +
>>> +static void idle_sync_thread(struct mddev *mddev)
>>> +{
>>>          if (mddev_lock(mddev)) {
>>>                  mutex_unlock(&mddev->sync_mutex);
>>>                  return;
>>>          }
>>>
>>> +       mutex_lock(&mddev->sync_mutex);
>>> +       clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
>>>          stop_sync_thread(mddev, false, true);
>>>          mutex_unlock(&mddev->sync_mutex);
>>>   }
>>>
>>>   static void frozen_sync_thread(struct mddev *mddev)
>>>   {
>>> -       mutex_lock(&mddev->sync_mutex);
>>> -       set_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
>>> -
>>>          if (mddev_lock(mddev)) {
>>>                  mutex_unlock(&mddev->sync_mutex);
>>>                  return;
>>>          }
>>>
>>> +       mutex_lock(&mddev->sync_mutex);
>>> +       set_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
>>>          stop_sync_thread(mddev, false, false);
>>>          mutex_unlock(&mddev->sync_mutex);
>>>   }
>>> diff --git a/drivers/md/md.h b/drivers/md/md.h
>>> index 8d881cc59799..437ab70ce79b 100644
>>> --- a/drivers/md/md.h
>>> +++ b/drivers/md/md.h
>>> @@ -781,6 +781,9 @@ extern void md_rdev_clear(struct md_rdev *rdev);
>>>   extern void md_handle_request(struct mddev *mddev, struct bio *bio);
>>>   extern int mddev_suspend(struct mddev *mddev, bool interruptible);
>>>   extern void mddev_resume(struct mddev *mddev);
>>> +extern void md_idle_sync_thread(struct mddev *mddev);
>>> +extern void md_frozen_sync_thread(struct mddev *mddev);
>>> +extern void md_unfrozen_sync_thread(struct mddev *mddev);
>>>
>>>   extern void md_reload_sb(struct mddev *mddev, int raid_disk);
>>>   extern void md_update_sb(struct mddev *mddev, int force);
>>> -- 
>>> 2.39.2
>>>
>>
>> .
>>
> 
> .
>