Re: After reshaping raid1 to raid0 with bitmap, then stop md panic

[NeilBrown <neilb@suse.de>]

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On Tue, 5 Aug 2014 03:03:06 -0400 (EDT) Xiao Ni <xni@redhat.com> wrote:

> Dear all
> 
> 
>    I faced one problem that the system panic after reshaping raid1 to raid0 with bitmap.
> The dmesg and calltrace information is like this:
> 
>    You can easily reproduce this by those steps:
>    1. mdadm -CR /dev/md0 -l1 -n2 /dev/loop[0-1] --bitmap=internal
>    2. mdadm --wait /dev/md0
>    3. mdadm --grow -l0 /dev/md0
>    4. mdadm -S /dev/md0
...
> 
> [ 1485.646746] BUG: unable to handle kernel NULL pointer dereference at 0000000000000038
> [ 1485.654724] IP: [<ffffffff8148db2e>] bitmap_daemon_work+0x24e/0x450

Yes, RAID0 doesn't support bitmaps, so this cannot possibly work.

Following patch should turn the crash into a clean failure.

Thanks for the report,
NeilBrown


From 1bdb20e16166240a4ca3b861c48defefaf218874 Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb@suse.de>
Date: Wed, 6 Aug 2014 16:34:27 +1000
Subject: [PATCH] md: check for bitmap compatability when changing raid levels.

If an array has a bitmap, then it cannot be converted to
a level which does not support bitmaps.

Reported-by: Xiao Ni <xni@redhat.com>
Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 1379b1a3b9ff..3bd13b276e45 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -3500,6 +3500,12 @@ level_store(struct mddev *mddev, const char *buf, size_t len)
 		       mdname(mddev), clevel);
 		return -EINVAL;
 	}
+	if (mddev->bitmap && !pers->quiesce) {
+		module_put(pers->owner);
+		printk(KERN_WARNING "md: %s: %s does not support a bitmap\n",
+		       mdname(mddev), clevel);
+		return -EINVAL;
+	}
 
 	rdev_for_each(rdev, mddev)
 		rdev->new_raid_disk = rdev->raid_disk;

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