linux-kernel - Re: [PATCH 1/2] md: fix WARN_ON if create symlink fail in bind_rdev_to

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Message-ID: <3cf95141-0cdb-9e67-16a9-4c64b3251885@huaweicloud.com>
Date: Mon, 25 Dec 2023 09:35:24 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Song Liu <song@...nel.org>, Li Nan <linan666@...weicloud.com>
Cc: linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
 yi.zhang@...wei.com, houtao1@...wei.com, yangerkun@...wei.com,
 "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH 1/2] md: fix WARN_ON if create symlink fail in
 bind_rdev_to_array()

Hi,

在 2023/12/25 9:11, Song Liu 写道:
> On Thu, Dec 21, 2023 at 5:17 PM Li Nan <linan666@...weicloud.com> wrote:
>>
>>
>>
>> 在 2023/12/22 2:58, Song Liu 写道:
> [...]
>>> In general, I would like to avoid adding flags if possible.
>>>
>>
>> This flag is mainly used to fix deadlock in next patch. Or should we
>> export bd_find_holder_disk()? Link hodler if it return NULL.
>> just like:
>>
>>     rdev_for_each_rcu
>>       if (!bd_find_holder_disk)
>>         bd_link_disk_holder
> 
> I was thinking we will not need the flag if we fail bind_rdev_to_array()
> on error (below).
> 
>>
>>
>>>>    };
>>>>
>>>>    static inline int is_badblock(struct md_rdev *rdev, sector_t s, int sectors,
>>>> diff --git a/drivers/md/md.c b/drivers/md/md.c
>>>> index e05858653a41..d6612b922c76 100644
>>>> --- a/drivers/md/md.c
>>>> +++ b/drivers/md/md.c
>>>> @@ -2526,7 +2526,8 @@ static int bind_rdev_to_array(struct md_rdev *rdev, struct mddev *mddev)
>>>>                   sysfs_get_dirent_safe(rdev->kobj.sd, "bad_blocks");
>>>>
>>>>           list_add_rcu(&rdev->same_set, &mddev->disks);
>>>> -       bd_link_disk_holder(rdev->bdev, mddev->gendisk);
>>>> +       if (!bd_link_disk_holder(rdev->bdev, mddev->gendisk))
>>>> +               set_bit(SymlinkCreated, &rdev->flags);
>>>
>>> Shall we just fail bind_rdev_to_array() if bd_link_disk_holder()
>>> returns non-zero?
>>>
>>
>> I keep this action because of commit 00bcb4ac7ee7 ("md: reduce
>> dependence on sysfs."). Fail bind_rdev_to_array is good to me.
> 
> I wonder whether the assumption in 00bcb4ac7ee7 is still true. If
> bd_link_disk_holder() fails for valid reasons, we need to handle it
> properly (set a flag, check the flag on unlink, etc.). If we only fail
> bd_link_disk_holder() on extreme cases (ENOMEM, etc.), we can
> just fail bind_rdev_to_array().

I totally agree! Currently, bd_link_disk_holder() from md won't return
-EINVAL, it will return -ENOMEM or -ENODEV if underlying disk is
deleted, which means bind_rdev_to_array() should fail as well.

The only problem is that this will make next patch more complicated, but
I think this can be solved.

Thanks,
Kuai
> 
> Thanks,
> Song
> .
>