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>

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 866825f..25d4542 100644 (file)
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -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_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);
+       /* 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));
 
        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);

diff --git a/drivers/md/md.h b/drivers/md/md.h
index b5c4be7..03b19aa 100644 (file)
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -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;