[PATCH 4.19 335/346] md/cluster: fix deadlock when node is doing resync job

Greg Kroah-Hartman
2020-12-28T13:36:30Z

From: Zhao Heming <heming.zhao@suse.com>

commit bca5b0658020be90b6b504ca514fd80110204f71 upstream.

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 : MD_CLUSTER_SEND_LOCK is 1.

d. B recv METADATA_UPDATED msg, which send from A in step .
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.

Cc: stable@vger.kernel.org
Signed-off-by: Zhao Heming <heming.zhao@suse.com>
Suggested-by: Xiao Ni <xni@redhat.com>
Reviewed-by: Xiao Ni <xni@redhat.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/md/md-cluster.c | 67 +++++++++++++++++++++++++++---------------------
drivers/md/md.c | 6 ++--
2 files changed, 42 insertions(+), 31 deletions(-)

--- a/drivers/md/md-cluster.c
+++ b/drivers/md/md-cluster.c
@@ -669,9 +669,27 @@ out:
* 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;

/*
@@ -682,34 +700,19 @@ static int lock_token(struct md_cluster_
*/
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);
+ 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)
@@ -789,9 +792,11 @@ static int sendmsg(struct md_cluster_inf
{
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;
}

@@ -1063,7 +1068,7 @@ static int metadata_update_start(struct
return 0;
}

- ret = lock_token(cinfo, 1);
+ ret = lock_token(cinfo);
clear_bit_unlock(MD_CLUSTER_HOLDING_MUTEX_FOR_RECVD, &cinfo->state);
return ret;
}
@@ -1181,7 +1186,10 @@ static void update_size(struct mddev *md
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);
@@ -1330,7 +1338,8 @@ static int add_new_disk(struct mddev *md
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);
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -6564,8 +6564,10 @@ static int hot_remove_disk(struct mddev
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);