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authorZhao Heming <heming.zhao@suse.com>2020-11-19 19:41:34 +0800
committerSong Liu <songliubraving@fb.com>2020-11-30 10:12:35 -0800
commitbca5b0658020be90b6b504ca514fd80110204f71 (patch)
tree3b8b7720717d782c081c6af0d8b455c688fa72f4 /drivers/md/md.c
parenta8da01f79c89755fad55ed0ea96e8d2103242a72 (diff)
md/cluster: fix deadlock when node is doing resync job
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>
Diffstat (limited to 'drivers/md/md.c')
-rw-r--r--drivers/md/md.c6
1 files changed, 4 insertions, 2 deletions
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 90faec048f2c..c42af46d366a 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -6953,8 +6953,10 @@ 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);