RE: Software raid0 will crash the file-system, when each disk is 5TB

[Neil Brown]

On Friday May 18, [EMAIL PROTECTED] wrote:
>  Fix confirmed, filled the whole 11T hard disk, without crashing.
> I presume this would go into 2.6.22

Yes, and probably 2.6.21.y, though the patch will be slightly
different, see below.
> 
> Thanks again.

And thank-you for pursuing this with me.

NeilBrown


---
Avoid overflow in raid0 calculation with large components.

If a raid0 has a component device larger than 4TB, and is accessed on
a 32bit machines, then as 'chunk' is unsigned lock,
   chunk << chunksize_bits
can overflow (this can be as high as the size of the device in KB).
chunk itself will not overflow (without triggering a BUG).

So change 'chunk' to be 'sector_t, and get rid of the 'BUG' as it becomes
impossible to hit.

Cc: "Jeff Zheng" <[EMAIL PROTECTED]>
Signed-off-by: Neil Brown <[EMAIL PROTECTED]>

### Diffstat output
 ./drivers/md/raid0.c |3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff .prev/drivers/md/raid0.c ./drivers/md/raid0.c
--- .prev/drivers/md/raid0.c2007-05-17 10:33:30.0 +1000
+++ ./drivers/md/raid0.c2007-05-17 16:14:12.0 +1000
@@ -415,7 +415,7 @@ static int raid0_make_request (request_q
raid0_conf_t *conf = mddev_to_conf(mddev);
struct strip_zone *zone;
mdk_rdev_t *tmp_dev;
-   unsigned long chunk;
+   sector_t chunk;
sector_t block, rsect;
const int rw = bio_data_dir(bio);
 
@@ -470,7 +470,6 @@ static int raid0_make_request (request_q
 
sector_div(x, zone->nb_dev);
chunk = x;
-   BUG_ON(x != (sector_t)chunk);
 
x = block >> chunksize_bits;
tmp_dev = zone->dev[sector_div(x, zone->nb_dev)];
-
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RE: Software raid0 will crash the file-system, when each disk is 5TB

[Jeff Zheng]

 Fix confirmed, filled the whole 11T hard disk, without crashing.
I presume this would go into 2.6.22

Thanks again.

Jeff

> -Original Message-
> From: [EMAIL PROTECTED] 
> [mailto:[EMAIL PROTECTED] On Behalf Of Jeff Zheng
> Sent: Thursday, 17 May 2007 5:39 p.m.
> To: Neil Brown; [EMAIL PROTECTED]; Michal Piotrowski; Ingo 
> Molnar; linux-raid@vger.kernel.org; 
> [EMAIL PROTECTED]; [EMAIL PROTECTED]
> Subject: RE: Software raid0 will crash the file-system, when 
> each disk is 5TB
> 
> 
> Yeah, seems you've locked it down, :D. I've written 600GB of 
> data now, and anything is still fine.
> Will let it run overnight, and fill the whole 11T. I'll post 
> the result tomorrow
> 
> Thanks a lot though.
> 
> Jeff 
> 
> > -Original Message-
> > From: Neil Brown [mailto:[EMAIL PROTECTED]
> > Sent: Thursday, 17 May 2007 5:31 p.m.
> > To: [EMAIL PROTECTED]; Jeff Zheng; Michal Piotrowski; Ingo Molnar; 
> > linux-raid@vger.kernel.org; [EMAIL PROTECTED]; 
> > [EMAIL PROTECTED]
> > Subject: RE: Software raid0 will crash the file-system, 
> when each disk 
> > is 5TB
> > 
> > On Thursday May 17, [EMAIL PROTECTED] wrote:
> > > 
> > > Uhm, I just noticed something.
> > > 'chunk' is unsigned long, and when it gets shifted up, we
> > might lose
> > > bits.  That could still happen with the 4*2.75T 
> arrangement, but is 
> > > much more likely in the 2*5.5T arrangement.
> > 
> > Actually, it cannot be a problem with the 4*2.75T arrangement.
> >   chuck << chunksize_bits
> > 
> > will not exceed the size of the underlying device *in*kilobytes*.
> > In that case that is 0xAE9EC800 which will git in a 32bit long.
> > We don't double it to make sectors until after we add
> > zone->dev_offset, which is "sector_t" and so 64bit 
> arithmetic is used.
> > 
> > So I'm quite certain this bug will cause exactly the problems 
> > experienced!!
> > 
> > > 
> > > Jeff, can you try this patch?
> > 
> > Don't bother about the other tests I mentioned, just try this one.
> > Thanks.
> > 
> > NeilBrown
> > 
> > > Signed-off-by: Neil Brown <[EMAIL PROTECTED]>
> > > 
> > > ### Diffstat output
> > >  ./drivers/md/raid0.c |2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff .prev/drivers/md/raid0.c ./drivers/md/raid0.c
> > > --- .prev/drivers/md/raid0.c  2007-05-17 
> > 10:33:30.0 +1000
> > > +++ ./drivers/md/raid0.c  2007-05-17 15:02:15.0 +1000
> > > @@ -475,7 +475,7 @@ static int raid0_make_request (request_q
> > >   x = block >> chunksize_bits;
> > >   tmp_dev = zone->dev[sector_div(x, zone->nb_dev)];
> > >   }
> > > - rsect = (((chunk << chunksize_bits) + zone->dev_offset)<<1)
> > > + rsect = sector_t)chunk << chunksize_bits) +
> > > +zone->dev_offset)<<1)
> > >   + sect_in_chunk;
> > >   
> > >   bio->bi_bdev = tmp_dev->bdev;
> > 
> -
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> 
-
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