Commit bb8bf15b authored Jun 02, 2016 by Guoqing Jiang Committed by Shaohua Li Jun 03, 2016

md-cluster: fix deadlock issue when add disk to an recoverying array



Add a disk to an array which is performing recovery
is a little complicated, we need to do both reap the
sync thread and perform add disk for the case, then
it caused deadlock as follows.

linux44:~ # ps aux|grep md|grep D
root      1822  0.0  0.0      0     0 ?        D    16:50   0:00 [md127_resync]
root      1848  0.0  0.0  19860   952 pts/0    D+   16:50   0:00 mdadm --manage /dev/md127 --re-add /dev/vdb
linux44:~ # cat /proc/1848/stack
[<ffffffff8107afde>] kthread_stop+0x6e/0x120
[<ffffffffa051ddb0>] md_unregister_thread+0x40/0x80 [md_mod]
[<ffffffffa0526e45>] md_reap_sync_thread+0x15/0x150 [md_mod]
[<ffffffffa05271e0>] action_store+0x260/0x270 [md_mod]
[<ffffffffa05206b4>] md_attr_store+0xb4/0x100 [md_mod]
[<ffffffff81214a7e>] sysfs_write_file+0xbe/0x140
[<ffffffff811a6b98>] vfs_write+0xb8/0x1e0
[<ffffffff811a75b8>] SyS_write+0x48/0xa0
[<ffffffff8152a5c9>] system_call_fastpath+0x16/0x1b
[<00007f068ea1ed30>] 0x7f068ea1ed30
linux44:~ # cat /proc/1822/stack
[<ffffffffa05251a6>] md_do_sync+0x846/0xf40 [md_mod]
[<ffffffffa052402d>] md_thread+0x16d/0x180 [md_mod]
[<ffffffff8107ad94>] kthread+0xb4/0xc0
[<ffffffff8152a518>] ret_from_fork+0x58/0x90

                        Task1848                                Task1822
md_attr_store (held reconfig_mutex by call mddev_lock())
                        action_store
			md_reap_sync_thread
			md_unregister_thread
			kthread_stop                    md_wakeup_thread(mddev->thread);
						wait_event(mddev->sb_wait, !test_bit(MD_CHANGE_PENDING))

md_check_recovery is triggered by wakeup mddev->thread,
but it can't clear MD_CHANGE_PENDING flag since it can't
get lock which was held by md_attr_store already.

To solve the deadlock problem, we move "->resync_finish()"
from md_do_sync to md_reap_sync_thread (after md_update_sb),
also MD_HELD_RESYNC_LOCK is introduced since it is possible
that node can't get resync lock in md_do_sync.

Then we do not need to wait for MD_CHANGE_PENDING is cleared
or not since metadata should be updated after md_update_sb,
so just call resync_finish if MD_HELD_RESYNC_LOCK is set.

We also unified the code after skip label, since set PENDING
for non-clustered case should be harmless.

Reviewed-by: NeilBrown <neilb@suse.com>
Signed-off-by: Guoqing Jiang <gqjiang@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

parent 41257580

drivers/md/md.c

+11 −12

Original line number	Diff line number	Diff line
		@@ -7809,6 +7809,7 @@ void md_do_sync(struct md_thread *thread)
		if (ret)
		goto skip;

		set_bit(MD_CLUSTER_RESYNC_LOCKED, &mddev->flags);
		if (!(test_bit(MD_RECOVERY_SYNC, &mddev->recovery) \|\|
		test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery) \|\|
		test_bit(MD_RECOVERY_RECOVER, &mddev->recovery))
		@@ -8147,18 +8148,11 @@ void md_do_sync(struct md_thread *thread)
		}
		}
		skip:
		if (mddev_is_clustered(mddev) &&
		ret == 0) {
		/* set CHANGE_PENDING here since maybe another
		* update is needed, so other nodes are informed */
		/* set CHANGE_PENDING here since maybe another update is needed,
		* so other nodes are informed. It should be harmless for normal
		* raid */
		set_mask_bits(&mddev->flags, 0,
		BIT(MD_CHANGE_PENDING) \| BIT(MD_CHANGE_DEVS));
		md_wakeup_thread(mddev->thread);
		wait_event(mddev->sb_wait,
		!test_bit(MD_CHANGE_PENDING, &mddev->flags));
		md_cluster_ops->resync_finish(mddev);
		} else
		set_bit(MD_CHANGE_DEVS, &mddev->flags);

		spin_lock(&mddev->lock);
		if (!test_bit(MD_RECOVERY_INTR, &mddev->recovery)) {
		@@ -8502,6 +8496,11 @@ void md_reap_sync_thread(struct mddev *mddev)
		rdev->saved_raid_disk = -1;

		md_update_sb(mddev, 1);
		/* MD_CHANGE_PENDING should be cleared by md_update_sb, so we can
		* call resync_finish here if MD_CLUSTER_RESYNC_LOCKED is set by
		* clustered raid */
		if (test_and_clear_bit(MD_CLUSTER_RESYNC_LOCKED, &mddev->flags))
		md_cluster_ops->resync_finish(mddev);
		clear_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
		clear_bit(MD_RECOVERY_DONE, &mddev->recovery);
		clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);

drivers/md/md.h

+3 −0

Original line number	Diff line number	Diff line
		@@ -204,6 +204,9 @@ struct mddev {
		#define MD_RELOAD_SB 7 /* Reload the superblock because another node
		* updated it.
		*/
		#define MD_CLUSTER_RESYNC_LOCKED 8 /* cluster raid only, which means node
		* already took resync lock, need to
		* release the lock */

		int suspended;
		atomic_t active_io;

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