[PATCH v2] md/cluster: block reshape requests with resync job initiated from remote node

[Zhao Heming <heming.zhao@suse.com>]

In cluster env, a node can start resync job when the resync cmd was
executed on a different node. Reshape requests should be blocked for
resync job initiated by any node. Current code only checks local resync
condition to block reshape requests. This results in a chaos result when
resync was doing on different node. 

Fix this by adding the extra check MD_RESYNCING_REMOTE.


*** Repro steps ***

Test env

node A & B share 3 iSCSI luns: sdg/sdh/sdi. Each lun size is 1GB. The
disk size is more large the issue is more likely to trigger. 
(more resync time, more easily trigger issue)

Test script

```
ssh root@node2 "mdadm -S --scan"
mdadm -S --scan
mdadm --zero-superblock /dev/sd{g,h,i}
for i in {g,h,i};do dd if=/dev/zero of=/dev/sd$i oflag=direct bs=1M \
count=20; done

echo "mdadm create array"
mdadm -C /dev/md0 -b clustered -e 1.2 -n 2 -l mirror /dev/sdg /dev/sdh
echo "set up array on node2"
ssh root@node2 "mdadm -A /dev/md0 /dev/sdg /dev/sdh"

sleep 5

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 --wait /dev/md0
mdadm --grow --raid-devices=2 /dev/md0
```

There is a workaround:
when adding the --wait before second --grow, the issue will disappear.

Test results

Every cmd line in test script can be finish, but array status is wrong.
There are 3 results.  (part of output by: mdadm -D /dev/md0)

<case 1> : normal test result.
```
    Number   Major   Minor   RaidDevice State
       1       8      112        0      active sync   /dev/sdh
       2       8      128        1      active sync   /dev/sdi
```

<case 2> : "--faulty" data still exist on disk metadata area.
```
    Number   Major   Minor   RaidDevice State
       -       0        0        0      removed
       1       8      112        1      active sync   /dev/sdh
       2       8      128        2      active sync   /dev/sdi

       0       8       96        -      faulty   /dev/sdg
```

<case 3> : "--remove" data still exist on disk metadata area.
```
    Number   Major   Minor   RaidDevice State
       -       0        0        0      removed
       1       8      112        1      active sync   /dev/sdh
       2       8      128        2      active sync   /dev/sdi
```

*** Analysis ***

code flow of the problem scenario

```
  node A                           node B
------------------------------   ---------------
mdadm --grow -n 3 md0
 + raid1_reshape
    mddev->raid_disks: 2=>3
                                 start resync job, it will block A resync job
                                 mddev->raid_disks: 2=>3

mdadm md0 --fail sdg
 + update disk: array sb & bitmap sb
 + send METADATA_UPDATE
 (resync job blocking)
                                 (B continue doing "--grow -n 3" resync job)
                                 recv METADATA_UPDATE
                                  + read disk metadata
                                  + raid1_error
                                  + set MD_RECOVERY_INTR to break resync
                                 ... ...
                                 md_check_recovery
                                  + remove_and_add_spares return 1
                                  + set MD_RECOVERY_RECOVER, later restart resync

mdadm md0 --remove sdg
 + md_cluster_ops->remove_disk
 |  + send REMOVE
 + md_kick_rdev_from_array
 + update disk: array sb & bitmap sb
 (resync job blocking)
                                 (B continue doing "--grow -n 3" resync job)
                                 recv REMOVE
                                  + process_remove_disk doesn't set mddev->sb_flags, 
                                     so it doesn't update disk sb & bitmap sb.
                                 ......
                                 md_check_recovery
                                  + md_kick_rdev_from_array 

mdadm --grow -n 2 md0
 + raid1_reshape
 |  mddev->raid_disks: 3=>2
 + send METADATA_UPDATED

                                 (B continue doing "--grow -n 3" resync job)
                                 recv METADATA_UPDATE
                                  + check_sb_changes
                                     update_raid_disks return -EBUSY
                                     update failed for mddev->raid_disks: 3=>2


                                (B never successfully update mddev->raid_disks: 3=>2)
                                when B finish "--grow -n 3" resync job
                                 + use mddev->raid_disks:3 to update array sb & bitmap sb
                                 + send METADATA_UPDATED

recv METADATA_UPDATED
 + read wrong raid_disks to update
   kernel data.
```

Signed-off-by: Zhao Heming <heming.zhao@suse.com>
---
v2:
- for clearly, split patch-v1 into two single patch to review.
- revise patch subject & comments. 
- add test result in comments.

v1:
- add cover-letter
- add more descriptions in commit log

v0:
- create 2 patches, patch 1/2 is this patch.

---
 drivers/md/md.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 98bac4f304ae..74280e353b8f 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -7278,6 +7278,7 @@ static int update_raid_disks(struct mddev *mddev, int raid_disks)
 		return -EINVAL;
 	if (mddev->sync_thread ||
 	    test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) ||
+		test_bit(MD_RESYNCING_REMOTE, &mddev->recovery) ||
 	    mddev->reshape_position != MaxSector)
 		return -EBUSY;
 
@@ -9662,8 +9663,11 @@ static void check_sb_changes(struct mddev *mddev, struct md_rdev *rdev)
 		}
 	}
 
-	if (mddev->raid_disks != le32_to_cpu(sb->raid_disks))
-		update_raid_disks(mddev, le32_to_cpu(sb->raid_disks));
+	if (mddev->raid_disks != le32_to_cpu(sb->raid_disks)) {
+		ret = update_raid_disks(mddev, le32_to_cpu(sb->raid_disks));
+		if (ret)
+			pr_warn("md: updating array disks failed. %d\n", ret);
+	}
 
 	/*
 	 * Since mddev->delta_disks has already updated in update_raid_disks,
-- 
2.27.0