Re: md: md6_raid5 crash 2.6.20

[Marc Marais]

On Mon, 12 Feb 2007 09:02:33 +1100, Neil Brown wrote
> On Sunday February 11, marcm@xxxxxxxxxxxxxxxx wrote:
> > Greetings,
> > 
> > I've been running md on my server for some time now and a few days ago one of
> > the (3) drives in the raid5 array starting giving read errors. The result was
> > usually system hangs and this was with kernel 2.6.17.13. I upgraded to the
> > latest production 2.6.20 kernel and experienced the same behaviour.
> 
> System hangs suggest a problem with the drive controller.  However
> this "kernel BUG" is something newly introduced in 2.6.20 which 
> should be fixed in 2.6.20.1.  Patch is below.
> 
> If you still get hangs with this patch installed, then please report
> detail, and probably copy to linux-ide@xxxxxxxxxxxxxxxx
> 
> NeilBrown
> 
> Fix various bugs with aligned reads in RAID5.
> 
> It is possible for raid5 to be sent a bio that is too big
> for an underlying device.  So if it is a READ that we
> pass stright down to a device, it will fail and confuse
> RAID5.
> 
> So in 'chunk_aligned_read' we check that the bio fits within the
> parameters for the target device and if it doesn't fit, fall back
> on reading through the stripe cache and making lots of one-page
> requests.
> 
> Note that this is the earliest time we can check against the device
> because earlier we don't have a lock on the device, so it could 
> change underneath us.
> 
> Also, the code for handling a retry through the cache when a read
> fails has not been tested and was badly broken.  This patch fixes 
> that code.
> 
> Signed-off-by: Neil Brown <neilb@xxxxxxx>
> 

Thanks for the quick response Neil unfortunately the kernel doesn't build with
this patch due to a missing symbol:

WARNING: "blk_recount_segments" [drivers/md/raid456.ko] undefined!

Is that in another file that needs patching or within raid5.c?

Marc

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