[dm-devel] Re: [PATCH] Fix panic in 2.6 with bounced bio and dm

[Mark Haverkamp]

On Sat, 2005-02-26 at 13:39 +0100, Jens Axboe wrote:
> On Fri, Feb 25 2005, Linus Torvalds wrote:
> > 
> > 
> > On Fri, 25 Feb 2005, Andrew Morton wrote:
> > > 
> > > It seems very weird for dm to be shoving NULL page*'s into the middle of a
> > > bio's bvec array, so your fix might end up being a workaround pending a
> > > closer look at what's going on in there.
> > 
> > Yes. I don't see how this patch can be anything but bandaid to hide the 
> > real bug. Where do these "non-page" bvec's originate?
> 
> Yep that's the fishy part, there should not be NULL pages in the middle
> (or empty bios, for that matter) submitted for io.
> 
> Mark, what was the bug that triggered you to write this patch?

It happened when some pages of IO from a dm device were bounced.  It
looks to me when bio's are cloned in the dm code to split it for
physical devices that only the pointers to pages that apply to that
device are copied and th bi_idx is adjusted to point to the start,
leaving some NULL pointers at the start of the bio_vec.

Mark,


> 
-- 
Mark Haverkamp <markh at osdl.org>