md/cluster: fix deadlock when node is doing resync job

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 <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.

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>

diff --git a/drivers/md/md-cluster.c b/drivers/md/md-cluster.c
index 4aaf482..f0e64e7 100644 (file)
--- a/drivers/md/md-cluster.c
+++ b/drivers/md/md-cluster.c
@@ -664,9 +664,27 @@ 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;
 
        /*
@@ -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)
@@ -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 55f9ddf..3be74cf 100644 (file)
--- 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);