mdadm/super1: restore commit 45a87c2f31335 to fix clustered slot issue

Commit 9d67f6496c71 ("mdadm:check the nodes when operate clustered
array") modified assignment logic for st->nodes in write_bitmap1(),
which introduced bitmap slot issue:

load_super1 didn't set up supertype.nodes, which made spare disk only
have one slot info. Then it triggered kernel md_bitmap_load_sb to get
wrong bitmap slot data.

For fixing this issue, there are two methods:

1> revert the related code of commit 9d67f6496c71. and restore the code
   from former commit 45a87c2f31335 ("super1: add more checks for
   NodeNumUpdate option").
   st->nodes value would be 0 & 1 under current code logic. i.e.
   When adding a spare disk, there is no place to init st->nodes, and
   the value is ZERO.

2> keep 9d67f6496c71, add additional ->nodes handling in load_super1(),
   let load_super1 to set st->nodes when bitmap is BITMAP_MAJOR_CLUSTERED.
   Under current mdadm code logic, load_super1 will be called many
   times, any new code in load_super1 will cost mdadm running more time.
   And more reason is I prefer as much as possible to limit clustered
   code spreading in every corner.

So I used method <1> to fix this issue.

How to trigger:

dd if=/dev/zero bs=1M count=1 oflag=direct of=/dev/sda
dd if=/dev/zero bs=1M count=1 oflag=direct of=/dev/sdb
dd if=/dev/zero bs=1M count=1 oflag=direct of=/dev/sdc
mdadm -C /dev/md0 -b clustered -e 1.2 -n 2 -l mirror /dev/sda /dev/sdb
mdadm -a /dev/md0 /dev/sdc
mdadm /dev/md0 --fail /dev/sda
mdadm /dev/md0 --remove /dev/sda
mdadm -Ss
mdadm -A /dev/md0 /dev/sdb /dev/sdc

the output of current "mdadm -X /dev/sdc":
(there should be (by default) 4 slot info for correct output)
```
        Filename : /dev/sdc
           Magic : 6d746962
         Version : 5
            UUID : a74642f8:a6b1fba8:58e1f8db:cfe7b082
          Events : 29
  Events Cleared : 0
           State : OK
       Chunksize : 64 MB
          Daemon : 5s flush period
      Write Mode : Normal
       Sync Size : 306176 (299.00 MiB 313.52 MB)
          Bitmap : 5 bits (chunks), 5 dirty (100.0%)
```

And mdadm later operations will trigger kernel output error message:
(triggered by "mdadm -A /dev/md0 /dev/sdb /dev/sdc")
```
kernel: md0: invalid bitmap file superblock: bad magic
kernel: md_bitmap_copy_from_slot can't get bitmap from slot 1
kernel: md-cluster: Could not gather bitmaps from slot 1
kernel: md0: invalid bitmap file superblock: bad magic
kernel: md_bitmap_copy_from_slot can't get bitmap from slot 2
kernel: md-cluster: Could not gather bitmaps from slot 2
kernel: md0: invalid bitmap file superblock: bad magic
kernel: md_bitmap_copy_from_slot can't get bitmap from slot 3
kernel: md-cluster: Could not gather bitmaps from slot 3
kernel: md-cluster: failed to gather all resyn infos
kernel: md0: detected capacity change from 0 to 612352
```

Acked-by: Coly Li <colyli@suse.de>
Signed-off-by: Heming Zhao <heming.zhao@suse.com>
Signed-off-by: Jes Sorensen <jsorensen@fb.com>

1 files changed, 11 insertions, 1 deletions

diff --git a/super1.c b/super1.c
index e3e2f954..3a0c69fd 100644
--- a/super1.c
+++ b/super1.c
@@ -2674,7 +2674,17 @@ static int write_bitmap1(struct supertype *st, int fd, enum bitmap_update update
 		}
 
 		if (bms->version == BITMAP_MAJOR_CLUSTERED) {
-			if (__cpu_to_le32(st->nodes) < bms->nodes) {
+			if (st->nodes == 1) {
+				/* the parameter for nodes is not valid */
+				pr_err("Warning: cluster-md at least needs two nodes\n");
+				return -EINVAL;
+			} else if (st->nodes == 0) {
+				/*
+				 * parameter "--nodes" is not specified, (eg, add a disk to
+				 * clustered raid)
+				 */
+				break;
+			} else if (__cpu_to_le32(st->nodes) < bms->nodes) {
 				/*
 				 * Since the nodes num is not increased, no
 				 * need to check the space enough or not,