Re: NULL pointer dereference in blk_queue_flag_set

[jkhsjdhjs <jkhsjdhjs@totally.rip>]

Hey Song,

thanks for the quick reply! I applied your patch on top of 5.17-rc2 and 
it fixes the issue:

[   15.394670] device-mapper: raid: Loading target version 1.15.1
[   15.395216] device-mapper: raid: Ignoring chunk size parameter for RAID 1
[   15.395224] device-mapper: raid: Choosing default region size of 4MiB
[   15.399865] md/raid1:mdX: active with 2 out of 2 mirrors

Best Regards,

Leon

On 02.02.22 07:57, Song Liu wrote:
> Hi Leon,
>
> On Tue, Feb 1, 2022 at 2:15 PM jkhsjdhjs <jkhsjdhjs@totally.rip> wrote:
>> Dear Song Liu,
>>
>> my kernel (5.17-rc2) experiences a NULL pointer dereference when
>> activating an LDM (Windows Logical Disk Manager) on Arch Linux using
>> ldmtool [1]. I have attached the relevant excerpt of dmesg. This bug
>> causes my LDM RAID to fail activating (see ldmtool-status.txt and
>> lsblk.txt). Since this worked fine with 5.16 I bisected the kernel and
>> found, that commit f51d46d0e7cb5b8494aa534d276a9d8915a2443d [2]
>> introduced the issue.
>>
>> I'm not sure what else to add, if there's more information I can
>> provide, please tell me. Otherwise I'll happily assist in fixing this
>> issue - if there's something I can do.
> Thanks for the report! And sorry for the bug.
>
> For the next step, could you please test whether the following change
> fixes the issue?
>
> Best,
> Song
>
> diff --git i/drivers/md/md.c w/drivers/md/md.c
> index 854cbf4234aa..18e987c644c6 100644
> --- i/drivers/md/md.c
> +++ w/drivers/md/md.c
> @@ -5868,10 +5868,6 @@ int md_run(struct mddev *mddev)
>                  nowait = nowait && blk_queue_nowait(bdev_get_queue(rdev->bdev));
>          }
>
> -       /* Set the NOWAIT flags if all underlying devices support it */
> -       if (nowait)
> -               blk_queue_flag_set(QUEUE_FLAG_NOWAIT, mddev->queue);
> -
>          if (!bioset_initialized(&mddev->bio_set)) {
>                  err = bioset_init(&mddev->bio_set, BIO_POOL_SIZE, 0,
> BIOSET_NEED_BVECS);
>                  if (err)
> @@ -6009,6 +6005,10 @@ int md_run(struct mddev *mddev)
>                  else
>                          blk_queue_flag_clear(QUEUE_FLAG_NONROT, mddev->queue);
>                  blk_queue_flag_set(QUEUE_FLAG_IO_STAT, mddev->queue);
> +
> +               /* Set the NOWAIT flags if all underlying devices support it */
> +               if (nowait)
> +                       blk_queue_flag_set(QUEUE_FLAG_NOWAIT, mddev->queue);
>          }
>          if (pers->sync_request) {
>                  if (mddev->kobj.sd &&