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

[Jens Axboe]

On Mon, Feb 28 2005, Mark Haverkamp wrote:
> 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.

This should fix it.

Signed-off-by: Jens Axboe <axboe at suse.de>


===== mm/highmem.c 1.55 vs edited =====
--- 1.55/mm/highmem.c	2005-01-08 06:44:13 +01:00
+++ edited/mm/highmem.c	2005-02-28 16:50:59 +01:00
@@ -425,7 +425,7 @@
 	 * at least one page was bounced, fill in possible non-highmem
 	 * pages
 	 */
-	bio_for_each_segment(from, *bio_orig, i) {
+	__bio_for_each_segment(from, *bio_orig, i) {
 		to = bio_iovec_idx(bio, i);
 		if (!to->bv_page) {
 			to->bv_page = from->bv_page;

-- 
Jens Axboe