linux-kernel - Re: [PATCH md-6.12 3/7] md: don't record new badblocks for faulty rdev

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Message-ID: <f704a35f-bb4c-67d5-e32e-37bed99a1f9e@huaweicloud.com>
Date: Mon, 2 Sep 2024 20:37:24 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Mariusz Tkaczyk <mariusz.tkaczyk@...ux.intel.com>,
 Yu Kuai <yukuai1@...weicloud.com>
Cc: mariusz.tkaczyk@...el.com, song@...nel.org, 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 md-6.12 3/7] md: don't record new badblocks for faulty
 rdev

Hi,

在 2024/09/02 16:55, Mariusz Tkaczyk 写道:
> On Sat, 31 Aug 2024 09:14:39 +0800
> Yu Kuai <yukuai1@...weicloud.com> wrote:
> 
>> Hi,
>>
>> 在 2024/08/30 18:28, Mariusz Tkaczyk 写道:
>>> On Fri, 30 Aug 2024 15:27:17 +0800
>>> Yu Kuai <yukuai1@...weicloud.com> wrote:
>>>    
>>>> From: Yu Kuai <yukuai3@...wei.com>
>>>>
>>>> Faulty will be checked before issuing IO to the rdev, however, rdev can
>>>> be faulty at any time, hence it's possible that rdev_set_badblocks()
>>>> will be called for faulty rdev. In this case, mddev->sb_flags will be
>>>> set and some other path can be blocked by updating super block.
>>>>
>>>> Since faulty rdev will not be accesed anymore, there is no need to
>>>> record new babblocks for faulty rdev and forcing updating super block.
>>>>
>>>> Noted this is not a bugfix, just prevent updating superblock in some
>>>> corner cases, and will help to slice a bug related to external
>>>> metadata[1].
>>>>
>>>> [1]
>>>> https://lore.kernel.org/all/f34452df-810b-48b2-a9b4-7f925699a9e7@linux.intel.com/
>>>>
>>>> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
>>>> ---
>>>>    drivers/md/md.c | 4 ++++
>>>>    1 file changed, 4 insertions(+)
>>>>
>>>> diff --git a/drivers/md/md.c b/drivers/md/md.c
>>>> index 675d89597c7b..a3f7f407fe42 100644
>>>> --- a/drivers/md/md.c
>>>> +++ b/drivers/md/md.c
>>>> @@ -9757,6 +9757,10 @@ int rdev_set_badblocks(struct md_rdev *rdev,
>>>> sector_t s, int sectors, {
>>>>    	struct mddev *mddev = rdev->mddev;
>>>>    	int rv;
>>>> +
>>>> +	if (test_bit(Faulty, &rdev->flags))
>>>> +		return 1;
>>>> +
>>>
>>> Blame is volatile, this is why we need a comment here :)
>>> Otherwise, someone may remove that.
>>
>> Perhaps something like following?
>>
>> /*
>>    * record new babblocks for faulty rdev will force unnecessary
>>    * super block updating.
>>    */
>>
> 
> Almost, we need to refer to external context because this is important to
> mention where to expect issues:
> 
> /*
>   * Recording new badblocks for faulty rdev will force unnecessary
>   * super block updating. This is fragile for external management because
>   * userspace daemon may trying to remove this device and deadlock may
>   * occur. This will be probably solved in the mdadm, but it is safer to avoid
>   * it.
>   */
> 
> In my testing, I observed that it improves failing bios and device removal
> path (recording badblock is simply expensive if there are many badblocks) so
> the devices are removed faster but I don't have data here, this is what I saw.

I'll mention this in the commit message, and add the above comment in
v2.

Thanks,
Kuai

> 
> Obviously, it is optimization.
> 
> Mariusz
> 
> .
>