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md/cluster: fix deadlock when node is doing resync job
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commit bca5b06 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 <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 0ba9597
("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>
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@zhaohem @gregkh
zhaohem authored and gregkh committed Dec 30, 2020
1 parent 3ace8d5 commit d27d194
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Showing 2 changed files with 42 additions and 31 deletions.
67 changes: 38 additions & 29 deletions drivers/md/md-cluster.c
View file
Expand Up @@ -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;

/*
Expand All @@ -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);
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)
Expand Down Expand Up @@ -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;
}

Expand Down Expand Up @@ -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;
}
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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);
Expand Down
6 changes: 4 additions & 2 deletions drivers/md/md.c
View file
Expand Up @@ -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);
Expand Down

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