Re: Infiniate systemd loop when power off the machine with multiple MD RAIDs
From: Yu Kuai
Date: Wed Aug 30 2023 - 22:29:01 EST
Hi, Acelan,
在 2023/08/28 21:50, Yu Kuai 写道:
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@xxxxxxxxx> 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.
I saw your reply:
https://lore.kernel.org/all/CAMz9Wg9VXJzZkKWCosm0_=Rz6gG9r3pCMrhvBZQVCQb8i0kd-w@xxxxxxxxxxxxxx/
But I didn't recieve you emails, please reply to me through this email
address: yukuai3@xxxxxxxxxx. yukuai1@xxxxxxxxxxxxxxx is just used for
sending, and I always missing emails from huaweicloud.com, my apologize
for this inconvenience, I have to do it this way due to my company
policy.
There is something interesting on test result:
At first, md122 is the root device, I guess this is why I can't repoduce
this problem in my local VM.
[ 14.478619] systemd-gpt-auto-generator[585]: md122p3: Root device
/dev/md122.
[ 14.481823] block md122: the capability attribute has been deprecated.
Then, before trying to stop md122, following log shows that md122 is
still mounted:
[ 1368.369926] [3462]: Remounting '/' read-only with options
'errors=remount-ro,stripe=128'.
[ 1368.396287] EXT4-fs (md122p3): re-mounted
6d53dc8e-3f45-4efa-bc0e-4af477fac217 ro. Quota mode: none.
And since then, there is no log aboug md_open(), which means no one
ever open md122 since this remount.
At last, there are lots of log shows that md122 can't be opened
exclusively:
[ 1368.812952] md122:systemd-shutdow bd_prepare_to_claim return -16
[ 1368.819189] md122:systemd-shutdow blkdev_get_by_dev return -16
Which indicate that md122 is still mounted, and systemd-shutdow can't
stop this array. This behaviour looks correct to me, because rootfs
can't be umounted while systemd-shutdown is still running.
However, there are some questions I don't have answers for now, I'm not
familiar with how systemd works:
1) In the normal case that raid is root device, how can systemd-shutdown
make progress and how is rootfs unmounted?
2) How does this scenario related to commit 12a6caf273240a.
I must read systemd source code to get answers, and it'll be appreciated
if someone has answers.
Thanks,
Kuai
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/@/)
.
.