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

[Xiao Ni <xni@redhat.com>]

----- Original Message -----
> From: "NeilBrown" <neilb@suse.de>
> To: "Xiao Ni" <xni@redhat.com>
> Cc: linux-raid@vger.kernel.org, "Jes Sorensen" <jes.sorensen@redhat.com>
> Sent: Friday, August 8, 2014 1:45:06 PM
> Subject: Re: After reshaping raid1 to raid0 with bitmap, then stop md panic
> 
> On Thu, 7 Aug 2014 20:29:13 +1000 NeilBrown <neilb@suse.de> wrote:
> 
> > On Thu, 7 Aug 2014 06:03:37 -0400 (EDT) Xiao Ni <xni@redhat.com> wrote:
> > 
> > > 
> > > 
> > > ----- Original Message -----
> > > > From: "NeilBrown" <neilb@suse.de>
> > > > To: "Xiao Ni" <xni@redhat.com>
> > > > Cc: linux-raid@vger.kernel.org, "Jes Sorensen"
> > > > <jes.sorensen@redhat.com>
> > > > Sent: Wednesday, August 6, 2014 2:37:02 PM
> > > > Subject: Re: After reshaping raid1 to raid0 with bitmap, then stop md
> > > > panic
> > > > 
> > > > 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;
> > > > 
> > > 
> > > Hi Neil
> > > 
> > >    I have tried the patch, but it can reshape to raid0 still, then stop
> > >    the raid0, the system
> > > panics.
> > > 
> > >    What does pers->quiesce mean? I'm not familiar with md code.
> > > 
> > > Best Regards
> > > Xiao
> > 
> > 
> > "quiesce" is a function that makes the array "quiescent" - it stops all IO
> > from happening.
> > The set_bitmap_file() function has:
> > 
> > 	if (mddev->pers) {
> > 		if (!mddev->pers->quiesce)
> > 			return -EBUSY;
> > 
> > 
> > So I thought it was safe to assume that if there was a quiesce function
> > then
> > the personality handled bitmaps.  Obviously not.
> > I'll have to fix that up...
> 
> Can you confirm that this works please?
> Thanks.
> 
> NeilBrown
> 
> From a8461a61c241a25afedbe493c13d98a6e0cf4246 Mon Sep 17 00:00:00 2001
> From: NeilBrown <neilb@suse.de>
> Date: Wed, 6 Aug 2014 16:34:27 +1000
> Subject: [PATCH] md/raid0: check for bitmap compatability when changing raid
>  levels.
> 
> If an array has a bitmap, then it cannot be converted to raid0.
> 
> Reported-by: Xiao Ni <xni@redhat.com>
> Signed-off-by: NeilBrown <neilb@suse.de>
> 
> diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
> index 407a99e46f69..cf91f5910c7c 100644
> --- a/drivers/md/raid0.c
> +++ b/drivers/md/raid0.c
> @@ -685,6 +685,12 @@ static void *raid0_takeover(struct mddev *mddev)
>  	 *  raid10 - assuming we have all necessary active disks
>  	 *  raid1 - with (N -1) mirror drives faulty
>  	 */
> +
> +	if (mddev->bitmap) {
> +		printk(KERN_ERR "md/raid0: %s: cannot takeover array with bitmap\n",
> +		       mdname(mddev));
> +		return ERR_PTR(-EBUSY);
> +	}
>  	if (mddev->level == 4)
>  		return raid0_takeover_raid45(mddev);
>  
> 
> 
> 
Hi Neil

   The problem can be fixed by this patch.

Best Regards
Xiao