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 --- 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);