[PATCH v4 0/2] md/cluster bugs fix

Hello List,

There are two patches to fix md-cluster bugs.

The 2 different bugs can use same test script to trigger:

ssh root@node2 "mdadm -S --scan"
mdadm -S --scan
for i in {g,h,i};do dd if=/dev/zero of=/dev/sd$i oflag=direct bs=1M \
count=20; done

echo "mdadm create array"
mdadm -C /dev/md0 -b clustered -e 1.2 -n 2 -l mirror /dev/sdg /dev/sdh \
--bitmap-chunk=1M
echo "set up array on node2"
ssh root@node2 "mdadm -A /dev/md0 /dev/sdg /dev/sdh"

sleep 5

mkfs.xfs /dev/md0
mdadm --manage --add /dev/md0 /dev/sdi
mdadm --wait /dev/md0
mdadm --grow --raid-devices=3 /dev/md0

mdadm /dev/md0 --fail /dev/sdg
mdadm /dev/md0 --remove /dev/sdg
mdadm --grow --raid-devices=2 /dev/md0

For detail, please check each patch commit log.

-------
v4:
- revise subject & commit log on both patches
- no change for code
v3:
- patch 1/2
  - no change
- patch 2/2
  - use Xiao's solution to fix
  - revise commit log for the "How to fix" part
v2:
- patch 1/2
  - change patch subject
  - add test result in commit log
  - no change for code
- patch 2/2
  - add test result in commit log
  - add error handling of remove_disk in hot_remove_disk
  - add error handling of lock_comm in all caller
  - remove 5s timeout fix in receive side (for process_metadata_update)
v1:
- create patch
-------
Zhao Heming (2):
  md/cluster: block reshape with remote resync job
  md/cluster: fix deadlock when node is doing resync job

 drivers/md/md-cluster.c | 69 +++++++++++++++++++++++------------------
 drivers/md/md.c         | 14 ++++++---
 2 files changed, 49 insertions(+), 34 deletions(-)

-- 
2.27.0

Reshape request should be blocked with ongoing resync job. In cluster
env, a node can start resync job even if the resync cmd isn't executed
on it, e.g., user executes "mdadm --grow" on node A, sometimes node B
will start resync job. However, current update_raid_disks() only check
local recovery status, which is incomplete. As a result, we see user will
execute "mdadm --grow" successfully on local, while the remote node deny
to do reshape job when it doing resync job. The inconsistent handling
cause array enter unexpected status. If user doesn't observe this issue
and continue executing mdadm cmd, the array doesn't work at last.

Fix this issue by blocking reshape request. When node executes "--grow"
and detects ongoing resync, it should stop and report error to user.

The following script reproduces the issue with ~100% probability.
(two nodes share 3 iSCSI luns: sdg/sdh/sdi. Each lun size is 1GB)

 # on node1, node2 is the remote node.
ssh root@node2 "mdadm -S --scan"
mdadm -S --scan
for i in {g,h,i};do dd if=/dev/zero of=/dev/sd$i oflag=direct bs=1M \
count=20; done

mdadm -C /dev/md0 -b clustered -e 1.2 -n 2 -l mirror /dev/sdg /dev/sdh
ssh root@node2 "mdadm -A /dev/md0 /dev/sdg /dev/sdh"

sleep 5

mdadm --manage --add /dev/md0 /dev/sdi
mdadm --wait /dev/md0
mdadm --grow --raid-devices=3 /dev/md0

mdadm /dev/md0 --fail /dev/sdg
mdadm /dev/md0 --remove /dev/sdg
mdadm --grow --raid-devices=2 /dev/md0

Signed-off-by: Zhao Heming <redacted>
---
 drivers/md/md.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 98bac4f304ae..74280e353b8f 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c

@@ -7278,6 +7278,7 @@ static int update_raid_disks(struct mddev *mddev, int raid_disks)
 		return -EINVAL;
 	if (mddev->sync_thread ||
 	    test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) ||
+	    test_bit(MD_RESYNCING_REMOTE, &mddev->recovery) ||
 	    mddev->reshape_position != MaxSector)
 		return -EBUSY;
 

@@ -9662,8 +9663,11 @@ static void check_sb_changes(struct mddev *mddev, struct md_rdev *rdev)
 		}
 	}
 
-	if (mddev->raid_disks != le32_to_cpu(sb->raid_disks))
-		update_raid_disks(mddev, le32_to_cpu(sb->raid_disks));
+	if (mddev->raid_disks != le32_to_cpu(sb->raid_disks)) {
+		ret = update_raid_disks(mddev, le32_to_cpu(sb->raid_disks));
+		if (ret)
+			pr_warn("md: updating array disks failed. %d\n", ret);
+	}
 
 	/*
 	 * Since mddev->delta_disks has already updated in update_raid_disks,

-- 
2.27.0

md-cluster uses MD_CLUSTER_SEND_LOCK to make node can exclusively send msg.
During sending msg, node can concurrently receive msg from another node.
When node does resync job, grab token_lockres:EX may trigger a deadlock:

nodeA                       nodeB
--------------------     --------------------
a.
send METADATA_UPDATED
held token_lockres:EX
                         b.
                         md_do_sync
                          resync_info_update
                            send RESYNCING
                             + set MD_CLUSTER_SEND_LOCK
                             + wait for holding token_lockres:EX

                         c.
                         mdadm /dev/md0 --remove /dev/sdg
                          + held reconfig_mutex
                          + send REMOVE
                             + wait_event(MD_CLUSTER_SEND_LOCK)

                         d.
                         recv_daemon //METADATA_UPDATED from A
                          process_metadata_update
                           + (mddev_trylock(mddev) ||
                              MD_CLUSTER_HOLDING_MUTEX_FOR_RECVD)
                             //this time, both return false forever

Explaination:
a. A send METADATA_UPDATED
   This will block another node to send msg

b. B does sync jobs, which will send RESYNCING at intervals.
   This will be block for holding token_lockres:EX lock.

c. B do "mdadm --remove", which will send REMOVE.
   This will be blocked by step <b>: MD_CLUSTER_SEND_LOCK is 1.

d. B recv METADATA_UPDATED msg, which send from A in step <a>.
   This will be blocked by step <c>: holding mddev lock, it makes
   wait_event can't hold mddev lock. (btw,
   MD_CLUSTER_HOLDING_MUTEX_FOR_RECVD keep ZERO in this scenario.)

There is a similar deadlock in commit 0ba959774e93
("md-cluster: use sync way to handle METADATA_UPDATED msg")
In that commit, step c is "update sb". This patch step c is
"mdadm --remove".

For fixing this issue, we can refer the solution of function:
metadata_update_start. Which does the same grab lock_token action.
lock_comm can use the same steps to avoid deadlock. By moving
MD_CLUSTER_HOLDING_MUTEX_FOR_RECVD from lock_token to lock_comm.
It enlarge a little bit window of MD_CLUSTER_HOLDING_MUTEX_FOR_RECVD,
but it is safe & can break deadlock.

Repro steps (I only triggered 3 times with hundreds tests):

two nodes share 3 iSCSI luns: sdg/sdh/sdi. Each lun size is 1GB.

ssh root@node2 "mdadm -S --scan"
mdadm -S --scan
for i in {g,h,i};do dd if=/dev/zero of=/dev/sd$i oflag=direct bs=1M \
count=20; done

mdadm -C /dev/md0 -b clustered -e 1.2 -n 2 -l mirror /dev/sdg /dev/sdh \
 --bitmap-chunk=1M
ssh root@node2 "mdadm -A /dev/md0 /dev/sdg /dev/sdh"

sleep 5

mkfs.xfs /dev/md0
mdadm --manage --add /dev/md0 /dev/sdi
mdadm --wait /dev/md0
mdadm --grow --raid-devices=3 /dev/md0

mdadm /dev/md0 --fail /dev/sdg
mdadm /dev/md0 --remove /dev/sdg
mdadm --grow --raid-devices=2 /dev/md0

test script will hung when executing "mdadm --remove".

 # dump stacks by "echo t > /proc/sysrq-trigger"
md0_cluster_rec D    0  5329      2 0x80004000
Call Trace:
 __schedule+0x1f6/0x560
 ? _cond_resched+0x2d/0x40
 ? schedule+0x4a/0xb0
 ? process_metadata_update.isra.0+0xdb/0x140 [md_cluster]
 ? wait_woken+0x80/0x80
 ? process_recvd_msg+0x113/0x1d0 [md_cluster]
 ? recv_daemon+0x9e/0x120 [md_cluster]
 ? md_thread+0x94/0x160 [md_mod]
 ? wait_woken+0x80/0x80
 ? md_congested+0x30/0x30 [md_mod]
 ? kthread+0x115/0x140
 ? __kthread_bind_mask+0x60/0x60
 ? ret_from_fork+0x1f/0x40

mdadm           D    0  5423      1 0x00004004
Call Trace:
 __schedule+0x1f6/0x560
 ? __schedule+0x1fe/0x560
 ? schedule+0x4a/0xb0
 ? lock_comm.isra.0+0x7b/0xb0 [md_cluster]
 ? wait_woken+0x80/0x80
 ? remove_disk+0x4f/0x90 [md_cluster]
 ? hot_remove_disk+0xb1/0x1b0 [md_mod]
 ? md_ioctl+0x50c/0xba0 [md_mod]
 ? wait_woken+0x80/0x80
 ? blkdev_ioctl+0xa2/0x2a0
 ? block_ioctl+0x39/0x40
 ? ksys_ioctl+0x82/0xc0
 ? __x64_sys_ioctl+0x16/0x20
 ? do_syscall_64+0x5f/0x150
 ? entry_SYSCALL_64_after_hwframe+0x44/0xa9

md0_resync      D    0  5425      2 0x80004000
Call Trace:
 __schedule+0x1f6/0x560
 ? schedule+0x4a/0xb0
 ? dlm_lock_sync+0xa1/0xd0 [md_cluster]
 ? wait_woken+0x80/0x80
 ? lock_token+0x2d/0x90 [md_cluster]
 ? resync_info_update+0x95/0x100 [md_cluster]
 ? raid1_sync_request+0x7d3/0xa40 [raid1]
 ? md_do_sync.cold+0x737/0xc8f [md_mod]
 ? md_thread+0x94/0x160 [md_mod]
 ? md_congested+0x30/0x30 [md_mod]
 ? kthread+0x115/0x140
 ? __kthread_bind_mask+0x60/0x60
 ? ret_from_fork+0x1f/0x40

At last, thanks for Xiao's solution.

Signed-off-by: Zhao Heming <redacted>
Suggested-by: Xiao Ni <redacted>
Reviewed-by: Xiao Ni <redacted>
---
 drivers/md/md-cluster.c | 69 +++++++++++++++++++++++------------------
 drivers/md/md.c         |  6 ++--
 2 files changed, 43 insertions(+), 32 deletions(-)

diff --git a/drivers/md/md-cluster.c b/drivers/md/md-cluster.c
index 4aaf4820b6f6..405bcc5d513e 100644
--- a/drivers/md/md-cluster.c
+++ b/drivers/md/md-cluster.c

@@ -664,9 +664,27 @@ static void recv_daemon(struct md_thread *thread)
  * Takes the lock on the TOKEN lock resource so no other
  * node can communicate while the operation is underway.
  */
-static int lock_token(struct md_cluster_info *cinfo, bool mddev_locked)
+static int lock_token(struct md_cluster_info *cinfo)
 {
-	int error, set_bit = 0;
+	int error;
+
+	error = dlm_lock_sync(cinfo->token_lockres, DLM_LOCK_EX);
+	if (error) {
+		pr_err("md-cluster(%s:%d): failed to get EX on TOKEN (%d)\n",
+				__func__, __LINE__, error);
+	} else {
+		/* Lock the receive sequence */
+		mutex_lock(&cinfo->recv_mutex);
+	}
+	return error;
+}
+
+/* lock_comm()
+ * Sets the MD_CLUSTER_SEND_LOCK bit to lock the send channel.
+ */
+static int lock_comm(struct md_cluster_info *cinfo, bool mddev_locked)
+{
+	int rv, set_bit = 0;
 	struct mddev *mddev = cinfo->mddev;
 
 	/*

@@ -677,34 +695,19 @@ static int lock_token(struct md_cluster_info *cinfo, bool mddev_locked)
 	 */
 	if (mddev_locked && !test_bit(MD_CLUSTER_HOLDING_MUTEX_FOR_RECVD,
 				      &cinfo->state)) {
-		error = test_and_set_bit_lock(MD_CLUSTER_HOLDING_MUTEX_FOR_RECVD,
+		rv = test_and_set_bit_lock(MD_CLUSTER_HOLDING_MUTEX_FOR_RECVD,
 					      &cinfo->state);
-		WARN_ON_ONCE(error);
+		WARN_ON_ONCE(rv);
 		md_wakeup_thread(mddev->thread);
 		set_bit = 1;
 	}
-	error = dlm_lock_sync(cinfo->token_lockres, DLM_LOCK_EX);
-	if (set_bit)
-		clear_bit_unlock(MD_CLUSTER_HOLDING_MUTEX_FOR_RECVD, &cinfo->state);
 
-	if (error)
-		pr_err("md-cluster(%s:%d): failed to get EX on TOKEN (%d)\n",
-				__func__, __LINE__, error);
-
-	/* Lock the receive sequence */
-	mutex_lock(&cinfo->recv_mutex);
-	return error;
-}
-
-/* lock_comm()
- * Sets the MD_CLUSTER_SEND_LOCK bit to lock the send channel.
- */
-static int lock_comm(struct md_cluster_info *cinfo, bool mddev_locked)
-{
 	wait_event(cinfo->wait,
-		   !test_and_set_bit(MD_CLUSTER_SEND_LOCK, &cinfo->state));
-
-	return lock_token(cinfo, mddev_locked);
+			   !test_and_set_bit(MD_CLUSTER_SEND_LOCK, &cinfo->state));
+	rv = lock_token(cinfo);
+	if (set_bit)
+		clear_bit_unlock(MD_CLUSTER_HOLDING_MUTEX_FOR_RECVD, &cinfo->state);
+	return rv;
 }
 
 static void unlock_comm(struct md_cluster_info *cinfo)

@@ -784,9 +787,11 @@ static int sendmsg(struct md_cluster_info *cinfo, struct cluster_msg *cmsg,
 {
 	int ret;
 
-	lock_comm(cinfo, mddev_locked);
-	ret = __sendmsg(cinfo, cmsg);
-	unlock_comm(cinfo);
+	ret = lock_comm(cinfo, mddev_locked);
+	if (!ret) {
+		ret = __sendmsg(cinfo, cmsg);
+		unlock_comm(cinfo);
+	}
 	return ret;
 }
 

@@ -1061,7 +1066,7 @@ static int metadata_update_start(struct mddev *mddev)
 		return 0;
 	}
 
-	ret = lock_token(cinfo, 1);
+	ret = lock_token(cinfo);
 	clear_bit_unlock(MD_CLUSTER_HOLDING_MUTEX_FOR_RECVD, &cinfo->state);
 	return ret;
 }

@@ -1255,7 +1260,10 @@ static void update_size(struct mddev *mddev, sector_t old_dev_sectors)
 	int raid_slot = -1;
 
 	md_update_sb(mddev, 1);
-	lock_comm(cinfo, 1);
+	if (lock_comm(cinfo, 1)) {
+		pr_err("%s: lock_comm failed\n", __func__);
+		return;
+	}
 
 	memset(&cmsg, 0, sizeof(cmsg));
 	cmsg.type = cpu_to_le32(METADATA_UPDATED);

@@ -1407,7 +1415,8 @@ static int add_new_disk(struct mddev *mddev, struct md_rdev *rdev)
 	cmsg.type = cpu_to_le32(NEWDISK);
 	memcpy(cmsg.uuid, uuid, 16);
 	cmsg.raid_slot = cpu_to_le32(rdev->desc_nr);
-	lock_comm(cinfo, 1);
+	if (lock_comm(cinfo, 1))
+		return -EAGAIN;
 	ret = __sendmsg(cinfo, &cmsg);
 	if (ret) {
 		unlock_comm(cinfo);

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 74280e353b8f..46da165afde2 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c

@@ -6948,8 +6948,10 @@ static int hot_remove_disk(struct mddev *mddev, dev_t dev)
 		goto busy;
 
 kick_rdev:
-	if (mddev_is_clustered(mddev))
-		md_cluster_ops->remove_disk(mddev, rdev);
+	if (mddev_is_clustered(mddev)) {
+		if (md_cluster_ops->remove_disk(mddev, rdev))
+			goto busy;
+	}
 
 	md_kick_rdev_from_array(rdev);
 	set_bit(MD_SB_CHANGE_DEVS, &mddev->sb_flags);

-- 
2.27.0

On 11/19/20 12:45 AM, Zhao Heming wrote:

md-cluster uses MD_CLUSTER_SEND_LOCK to make node can exclusively send msg.
During sending msg, node can concurrently receive msg from another node.
[... ...]

Repro steps (I only triggered 3 times with hundreds tests):

sorry to send v4 patch so late.
I spent more than 2 days to run test script to trigger the deadlock.
The result is I failed.
So I wrote "I only triggered 3 times with hundreds tests" in commit log.

two nodes share 3 iSCSI luns: sdg/sdh/sdi. Each lun size is 1GB.

ssh root@node2 "mdadm -S --scan"
[... ...]

At last, thanks for Xiao's solution.

Signed-off-by: Zhao Heming <heming.zhao@suse.com>
Suggested-by: Xiao Ni <xni@redhat.com>
Reviewed-by: Xiao Ni <xni@redhat.com>
---
  drivers/md/md-cluster.c | 69 +++++++++++++++++++++++------------------
  drivers/md/md.c         |  6 ++--
  2 files changed, 43 insertions(+), 32 deletions(-)

On Thu, Nov 19, 2020 at 12:45:53AM +0800, Zhao Heming wrote:

Reshape request should be blocked with ongoing resync job. In cluster
env, a node can start resync job even if the resync cmd isn't executed
on it, e.g., user executes "mdadm --grow" on node A, sometimes node B
will start resync job. However, current update_raid_disks() only check
local recovery status, which is incomplete. As a result, we see user will
execute "mdadm --grow" successfully on local, while the remote node deny
to do reshape job when it doing resync job. The inconsistent handling
cause array enter unexpected status. If user doesn't observe this issue
and continue executing mdadm cmd, the array doesn't work at last.

Fix this issue by blocking reshape request. When node executes "--grow"
and detects ongoing resync, it should stop and report error to user.

The following script reproduces the issue with ~100% probability.
(two nodes share 3 iSCSI luns: sdg/sdh/sdi. Each lun size is 1GB)

 # on node1, node2 is the remote node.
ssh root@node2 "mdadm -S --scan"
mdadm -S --scan
for i in {g,h,i};do dd if=/dev/zero of=/dev/sd$i oflag=direct bs=1M \
count=20; done

mdadm -C /dev/md0 -b clustered -e 1.2 -n 2 -l mirror /dev/sdg /dev/sdh
ssh root@node2 "mdadm -A /dev/md0 /dev/sdg /dev/sdh"

sleep 5

mdadm --manage --add /dev/md0 /dev/sdi
mdadm --wait /dev/md0
mdadm --grow --raid-devices=3 /dev/md0

mdadm /dev/md0 --fail /dev/sdg
mdadm /dev/md0 --remove /dev/sdg
mdadm --grow --raid-devices=2 /dev/md0

Signed-off-by: Zhao Heming <redacted>
---
 drivers/md/md.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>

On Thu, Nov 19, 2020 at 12:45:54AM +0800, Zhao Heming wrote:

md-cluster uses MD_CLUSTER_SEND_LOCK to make node can exclusively send msg.
During sending msg, node can concurrently receive msg from another node.
When node does resync job, grab token_lockres:EX may trigger a deadlock:

nodeA                       nodeB
--------------------     --------------------
a.
send METADATA_UPDATED
held token_lockres:EX
                         b.
                         md_do_sync
                          resync_info_update
                            send RESYNCING
                             + set MD_CLUSTER_SEND_LOCK
                             + wait for holding token_lockres:EX

                         c.
                         mdadm /dev/md0 --remove /dev/sdg
                          + held reconfig_mutex
                          + send REMOVE
                             + wait_event(MD_CLUSTER_SEND_LOCK)

                         d.
                         recv_daemon //METADATA_UPDATED from A
                          process_metadata_update
                           + (mddev_trylock(mddev) ||
                              MD_CLUSTER_HOLDING_MUTEX_FOR_RECVD)
                             //this time, both return false forever

Explaination:
a. A send METADATA_UPDATED
   This will block another node to send msg

b. B does sync jobs, which will send RESYNCING at intervals.
   This will be block for holding token_lockres:EX lock.

c. B do "mdadm --remove", which will send REMOVE.
   This will be blocked by step <b>: MD_CLUSTER_SEND_LOCK is 1.

d. B recv METADATA_UPDATED msg, which send from A in step <a>.
   This will be blocked by step <c>: holding mddev lock, it makes
   wait_event can't hold mddev lock. (btw,
   MD_CLUSTER_HOLDING_MUTEX_FOR_RECVD keep ZERO in this scenario.)

There is a similar deadlock in commit 0ba959774e93
("md-cluster: use sync way to handle METADATA_UPDATED msg")
In that commit, step c is "update sb". This patch step c is
"mdadm --remove".

For fixing this issue, we can refer the solution of function:
metadata_update_start. Which does the same grab lock_token action.
lock_comm can use the same steps to avoid deadlock. By moving
MD_CLUSTER_HOLDING_MUTEX_FOR_RECVD from lock_token to lock_comm.
It enlarge a little bit window of MD_CLUSTER_HOLDING_MUTEX_FOR_RECVD,
but it is safe & can break deadlock.

Repro steps (I only triggered 3 times with hundreds tests):

two nodes share 3 iSCSI luns: sdg/sdh/sdi. Each lun size is 1GB.

ssh root@node2 "mdadm -S --scan"
mdadm -S --scan
for i in {g,h,i};do dd if=/dev/zero of=/dev/sd$i oflag=direct bs=1M \
count=20; done

mdadm -C /dev/md0 -b clustered -e 1.2 -n 2 -l mirror /dev/sdg /dev/sdh \
 --bitmap-chunk=1M
ssh root@node2 "mdadm -A /dev/md0 /dev/sdg /dev/sdh"

sleep 5

mkfs.xfs /dev/md0
mdadm --manage --add /dev/md0 /dev/sdi
mdadm --wait /dev/md0
mdadm --grow --raid-devices=3 /dev/md0

mdadm /dev/md0 --fail /dev/sdg
mdadm /dev/md0 --remove /dev/sdg
mdadm --grow --raid-devices=2 /dev/md0

test script will hung when executing "mdadm --remove".

 # dump stacks by "echo t > /proc/sysrq-trigger"
md0_cluster_rec D    0  5329      2 0x80004000
Call Trace:
 __schedule+0x1f6/0x560
 ? _cond_resched+0x2d/0x40
 ? schedule+0x4a/0xb0
 ? process_metadata_update.isra.0+0xdb/0x140 [md_cluster]
 ? wait_woken+0x80/0x80
 ? process_recvd_msg+0x113/0x1d0 [md_cluster]
 ? recv_daemon+0x9e/0x120 [md_cluster]
 ? md_thread+0x94/0x160 [md_mod]
 ? wait_woken+0x80/0x80
 ? md_congested+0x30/0x30 [md_mod]
 ? kthread+0x115/0x140
 ? __kthread_bind_mask+0x60/0x60
 ? ret_from_fork+0x1f/0x40

mdadm           D    0  5423      1 0x00004004
Call Trace:
 __schedule+0x1f6/0x560
 ? __schedule+0x1fe/0x560
 ? schedule+0x4a/0xb0
 ? lock_comm.isra.0+0x7b/0xb0 [md_cluster]
 ? wait_woken+0x80/0x80
 ? remove_disk+0x4f/0x90 [md_cluster]
 ? hot_remove_disk+0xb1/0x1b0 [md_mod]
 ? md_ioctl+0x50c/0xba0 [md_mod]
 ? wait_woken+0x80/0x80
 ? blkdev_ioctl+0xa2/0x2a0
 ? block_ioctl+0x39/0x40
 ? ksys_ioctl+0x82/0xc0
 ? __x64_sys_ioctl+0x16/0x20
 ? do_syscall_64+0x5f/0x150
 ? entry_SYSCALL_64_after_hwframe+0x44/0xa9

md0_resync      D    0  5425      2 0x80004000
Call Trace:
 __schedule+0x1f6/0x560
 ? schedule+0x4a/0xb0
 ? dlm_lock_sync+0xa1/0xd0 [md_cluster]
 ? wait_woken+0x80/0x80
 ? lock_token+0x2d/0x90 [md_cluster]
 ? resync_info_update+0x95/0x100 [md_cluster]
 ? raid1_sync_request+0x7d3/0xa40 [raid1]
 ? md_do_sync.cold+0x737/0xc8f [md_mod]
 ? md_thread+0x94/0x160 [md_mod]
 ? md_congested+0x30/0x30 [md_mod]
 ? kthread+0x115/0x140
 ? __kthread_bind_mask+0x60/0x60
 ? ret_from_fork+0x1f/0x40

At last, thanks for Xiao's solution.

Signed-off-by: Zhao Heming <redacted>
Suggested-by: Xiao Ni <redacted>
Reviewed-by: Xiao Ni <redacted>
---
 drivers/md/md-cluster.c | 69 +++++++++++++++++++++++------------------
 drivers/md/md.c         |  6 ++--
 2 files changed, 43 insertions(+), 32 deletions(-)

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>