Re: Infiniate systemd loop when power off the machine with multiple MD RAIDs

[Yu Kuai <yukuai1@huaweicloud.com>]

Hi,

在 2023/08/28 13:20, Song Liu 写道:
> Hi AceLan,
> 
> Thanks for running the experiments.
> 
> On Fri, Aug 25, 2023 at 9:32 PM AceLan Kao <acelan@gmail.com> wrote:
> [...]
>>>
>>> Could you please run the follow two experiments?
>>>
>>> 1. Confirm 12a6caf273240a triggers this. Specifically:
>>>     git checkout 12a6caf273240a => repros
>>>     git checkout 12a6caf273240a~1 => cannot repro
>> Yes, I'm pretty sure about this, that's my bisect result and I just
>> confirmed it again.
>> I also tried reverting 12a6caf273240a and the issue is gone.
> 
> The log doesn't match my guess. Specifically:
> 
> [  420.068142] systemd-shutdown[1]: Stopping MD /dev/md123 (9:123).
> [  420.074718] md_open:md123 openers++ = 1 by systemd-shutdow
> [  420.080787] systemd-shutdown[1]: Failed to sync MD block device
> /dev/md123, ignoring: Input/output error
> [  420.090831] md: md123 stopped.
> [  420.094465] systemd-shutdown[1]: Stopping MD /dev/md122 (9:122).
> [  420.101045] systemd-shutdown[1]: Could not stop MD /dev/md122:
> Device or resource busy

I see that:

systemd-shutdown[1]: Couldn't finalize remaining  MD devices, trying again.

Can we make sure is this why power off hang?

Because in my VM, power off is not hang and I got:

systemd-shutdown[1]: Could not stop MD /dev/md1: Device or resource busy
systemd-shutdown[1]: Failed to finalize MD devices, ignoring.
> 
> For a successful stop on md123, we reach the pr_info() in md_open().
> For a failed stop on md122, the kernel returns -EBUSY before that
> pr_info() in md_open(). There are some changes in md_open() in
> the past few release, so I am not quite sure we are looking at the
> same code.

By the way, based on code review, looks like md_open never return
-EBUSY, and I think following is the only place can return -EBUSY before
md_open() is called:

blkdev_open
  blkdev_get_by_dev
   bd_prepare_to_claim
    bd_may_claim 	-> -EBUSY

Acelan, can you add following debug patch on the top of Song's patch
and reporduce it again? Hope it'll confirm why stop array failed with
-EBUSY.

diff --git a/block/bdev.c b/block/bdev.c
index 979e28a46b98..699739223dcb 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -789,8 +789,11 @@ struct block_device *blkdev_get_by_dev(dev_t dev, 
blk_mode_t mode, void *holder,
         if (holder) {
                 mode |= BLK_OPEN_EXCL;
                 ret = bd_prepare_to_claim(bdev, holder, hops);
-               if (ret)
+               if (ret) {
+                       pr_warn("%s:%s bd_prepare_to_claim return %d\n",
+                               disk->disk_name, current->comm, ret);
                         goto put_blkdev;
+               }
         } else {
                 if (WARN_ON_ONCE(mode & BLK_OPEN_EXCL)) {
                         ret = -EIO;
diff --git a/block/fops.c b/block/fops.c
index eaa98a987213..2d69119c71f6 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -587,8 +587,11 @@ static int blkdev_open(struct inode *inode, struct 
file *filp)

         bdev = blkdev_get_by_dev(inode->i_rdev, file_to_blk_mode(filp),
                                  filp->private_data, NULL);
-       if (IS_ERR(bdev))
+       if (IS_ERR(bdev)) {
+               pr_warn("%pD:%s blkdev_get_by_dev return %ld\n",
+                       filp, current->comm, PTR_ERR(bdev));
                 return PTR_ERR(bdev);
+       }

         if (bdev_nowait(bdev))
                 filp->f_mode |= FMODE_NOWAIT;

Thanks,
Kuai

> 
> Therefore, could you please help clarify:
> 
> 1. Which base kernel are you using?
> 
>>From the log, you are using 6.5-rc7-706a74159504. However,
> I think we cannot cleanly revert 12a6caf273240a on top of
> 6.5-rc7-706a74159504. Did you manually fix some issue in the
> revert? If so, could you please share the revert commit?
> 
> 2. If you are not using 6.5-rc7-706a74159504 as base kernel, which
> one are you using?
> 
> Thanks,
> Song
> 
>>
>>>
>>> 2. Try with the following change (add debug messages), which hopefully
>>>     shows which command is holding a reference on mddev->openers.
>>>
>>> Thanks,
>>> Song
>>>
>>> diff --git i/drivers/md/md.c w/drivers/md/md.c
>>> index 78be7811a89f..3e9b718b32c1 100644
>>> --- i/drivers/md/md.c
>>> +++ w/drivers/md/md.c
>>> @@ -7574,11 +7574,15 @@ static int md_ioctl(struct block_device *bdev,
>>> blk_mode_t mode,
>>>                  if (mddev->pers && atomic_read(&mddev->openers) > 1) {
>>>                          mutex_unlock(&mddev->open_mutex);
>>>                          err = -EBUSY;
>>> +                       pr_warn("%s return -EBUSY for %s with
>>> mddev->openers = %d\n",
>>> +                               __func__, mdname(mddev),
>>> atomic_read(&mddev->openers));
>>>                          goto out;
>>>                  }
>>>                  if (test_and_set_bit(MD_CLOSING, &mddev->flags)) {
>>>                          mutex_unlock(&mddev->open_mutex);
>>>                          err = -EBUSY;
>>> +                       pr_warn("%s return -EBUSY for %s with
>>> MD_CLOSING bit set\n",
>>> +                               __func__, mdname(mddev));
>>>                          goto out;
>>>                  }
>>>                  did_set_md_closing = true;
>>> @@ -7789,6 +7793,8 @@ static int md_open(struct gendisk *disk, blk_mode_t mode)
>>>                  goto out_unlock;
>>>
>>>          atomic_inc(&mddev->openers);
>>> +       pr_info("%s:%s openers++ = %d by %s\n", __func__, mdname(mddev),
>>> +               atomic_read(&mddev->openers), current->comm);
>>>          mutex_unlock(&mddev->open_mutex);
>>>
>>>          disk_check_media_change(disk);
>>> @@ -7807,6 +7813,8 @@ static void md_release(struct gendisk *disk)
>>>
>>>          BUG_ON(!mddev);
>>>          atomic_dec(&mddev->openers);
>>> +       pr_info("%s:%s openers-- = %d by %s\n", __func__, mdname(mddev),
>>> +               atomic_read(&mddev->openers), current->comm);
>>>          mddev_put(mddev);
>>>   }
>> It's pretty strange that I can't reproduce the issue after applied the patch.
>>
>> I tried to figure out which part affect the issue and found when I
>> comment out the pr_info() In md_release(), the issue could be
>> reproduced.
>>
>> --
>> Chia-Lin Kao(AceLan)
>> http://blog.acelan.idv.tw/
>> E-Mail: acelan.kaoATcanonical.com (s/AT/@/)
> .
>