linux-kernel - Re: [PATCH -next 3/7] md: don't rely on 'mddev->pers' to be set in mddev

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Message-ID: <2771400f-d4bb-d650-b075-0c2b56006545@huaweicloud.com>
Date:   Tue, 22 Aug 2023 10:08:48 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     Song Liu <song@...nel.org>, Yu Kuai <yukuai1@...weicloud.com>
Cc:     xni@...hat.com, linux-raid@...r.kernel.org,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
        yangerkun@...wei.com, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH -next 3/7] md: don't rely on 'mddev->pers' to be set in
 mddev_suspend()

Hi,

在 2023/08/22 8:13, Song Liu 写道:
> On Thu, Aug 3, 2023 at 6:30 AM Yu Kuai <yukuai1@...weicloud.com> wrote:
>>
>> From: Yu Kuai <yukuai3@...wei.com>
>>
>> Now that active io is initialized when mddev is allocated, it's safe to
>> call mddev_suspend() before 'mddev->pers' is set.
>>
>> This also prevent null-ptr-def in some cases that caller doesn't
>> guarantee 'mddev->pers' to be set.
> 
> This description is a little confusing (to me at least). Please revise it.

Sorry about this, how about this:

'active_io' used to be initialized while the array is running, and
'mddev->pers' is set while the array is running as well. Hence caller
must hold 'reconfig_mutex' and guarantee 'mddev->pers' is set before
calling mddev_suspend().

Now that 'active_io' is initialized when mddev is allocated, such
restriction doesn't exist anymore. In the meantime, follow up patches
will refactor mddev_suspend(), hence add checking for 'mddev->pers' to
prevent null-ptr-deref.

Thanks,
Kuai

> 
> Other than that, the set looks good to me.
> 
> Thanks,
> Song
> 
>>
>> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
>> ---
>>   drivers/md/md.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/md/md.c b/drivers/md/md.c
>> index 897e94a9e47d..f14f2f0a9484 100644
>> --- a/drivers/md/md.c
>> +++ b/drivers/md/md.c
>> @@ -448,7 +448,7 @@ void mddev_suspend(struct mddev *mddev)
>>          set_bit(MD_ALLOW_SB_UPDATE, &mddev->flags);
>>          percpu_ref_kill(&mddev->active_io);
>>
>> -       if (mddev->pers->prepare_suspend)
>> +       if (mddev->pers && mddev->pers->prepare_suspend)
>>                  mddev->pers->prepare_suspend(mddev);
>>
>>          wait_event(mddev->sb_wait, percpu_ref_is_zero(&mddev->active_io));
>> --
>> 2.39.2
>>
> .
>