[bug?] raid1 integrity checking is broken on 2.6.18-rc4

[Chuck Ebbert]

Doing this on a raid1 array:
        echo "check" >/sys/block/md0/md/sync_action

On 2.6.16.27:
        Activity lights on both mirrors show activity for a while,
        then the array status prints on the console.

On 2.6.18-rc4 + the below patch:
        Drive activity light blinks once on one drive, then the
        array status prints (obviously no checking takes place.)


Applied hotfix on 2.6.18-rc4:

--- .prev/drivers/md/md.c       2006-08-08 09:00:44.000000000 +1000
+++ ./drivers/md/md.c   2006-08-08 09:04:04.000000000 +1000
@@ -1597,6 +1597,19 @@ void md_update_sb(mddev_t * mddev)
 
 repeat:
        spin_lock_irq(&mddev->write_lock);
+
+       if (mddev->degraded && mddev->sb_dirty == 3)
+               /* If the array is degraded, then skipping spares is both
+                * dangerous and fairly pointless.
+                * Dangerous because a device that was removed from the array
+                * might have a event_count that still looks up-to-date,
+                * so it can be re-added without a resync.
+                * Pointless because if there are any spares to skip,
+                * then a recovery will happen and soon that array won't
+                * be degraded any more and the spare can go back to sleep then.
+                */
+               mddev->sb_dirty = 1;
+
        sync_req = mddev->in_sync;
        mddev->utime = get_seconds();
        if (mddev->sb_dirty == 3)
-- 
Chuck

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