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

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Message-ID: <d00e6729-6e13-b1ab-0991-ce79b1245cfd@huaweicloud.com>
Date: Fri, 22 Dec 2023 09:16:55 +0800
From: Li Nan <linan666@...weicloud.com>
To: Song Liu <song@...nel.org>, linan666@...weicloud.com
Cc: yukuai3@...wei.com, linux-raid@...r.kernel.org,
 linux-kernel@...r.kernel.org, yi.zhang@...wei.com, houtao1@...wei.com,
 yangerkun@...wei.com
Subject: Re: [PATCH 1/2] md: fix WARN_ON if create symlink fail in
 bind_rdev_to_array()



在 2023/12/22 2:58, Song Liu 写道:
> Hi,
> 
> On Wed, Dec 20, 2023 at 11:13 PM <linan666@...weicloud.com> wrote:
>>
>> From: Li Nan <linan122@...wei.com>
>>
>> Removing a device can trigger WARN_ON in bd_unlink_disk_holder() if creating
>> symlink failed while adding device.
>>
>>    WARNING: CPU: 0 PID: 742 at block/holder.c:145 bd_unlink_disk_holder+0x17b/0x1a0
>>
>> Fix it by adding the flag 'SymlinkCreated', which only be set after
>> creating symlink success.
>>
>> Signed-off-by: Li Nan <linan122@...wei.com>
>> ---
>>   drivers/md/md.h | 3 +++
>>   drivers/md/md.c | 8 ++++++--
>>   2 files changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/md/md.h b/drivers/md/md.h
>> index 8d881cc59799..427d17713a8c 100644
>> --- a/drivers/md/md.h
>> +++ b/drivers/md/md.h
>> @@ -207,6 +207,9 @@ enum flag_bits {
>>                                   * check if there is collision between raid1
>>                                   * serial bios.
>>                                   */
>> +       SymlinkCreated,         /* This device has created the symlink
>> +                                * with gendisk.
>> +                                */
> 
> 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


>>   };
>>
>>   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.

> Thanks,
> Song
> 
> .

-- 
Thanks,
Nan