On 2023-02-23 19:11, Hou Tao wrote:
> Hi,
>
> On 2/10/2023 10:10 AM, Li Nan wrote:
>> Hi,
>> Commit log says there is race condition in md_rdev_misc_wq, but I find nothing
>> wrong with it. Could you tell me how to trigger the bug?
>>
>> Thansks,
>> nan.
>>
> We want to back-port commit 5e8daf906f89 ("md: Flush workqueue md_rdev_misc_wq
> in md_alloc()") into v5.10 LTS, but only judging from its commit message, we
> don't know whether it is a good candidate or not. According to my understanding,
> the commit tries to wait for the deletion and the release of rdev kobject. The
> release of rdev kobject will call rdev_free() to free the allocated memory and
> it will not being related with any race, so I think the race mentioned in commit
> message must be related with the deletion of rdev kobject. Because the parent of
> rdev kobject is mddev and rdev kobject must have been acquired one reference of
> mddev kobject, so if the deletion of rdev kobject doesn't completes,
> md_kobj_release() and its callee del_gendisk() will be not called, right ? If
> the previous created mddev has not already called del_gendisk(), the current
> creation of mddev with the same name will fail in add_disk() or kobject_add(). I
> think this is the mentioned race in the commit message, right ? If that is the
> case, v5.10 LTS also have the same race problem. We will try to reproduce the
> problem and post it to v5.10 LTS.
Yes, that sounds correct. I expect v5.10 will have the same problem and
it is a good candidate to back port.
Logan
