On Wed, 30 Jul 2008, Theodore Tso wrote:
On Tue, Jul 29, 2008 at 10:03:38PM -0500, Eric Sandeen wrote:
Theodore Tso wrote:
Hmm... disassembling the code, it's pretty clear the problem is here
in do_split(), around line 1208:
map = (struct dx_map_entry *) (data2 + blocksize);
count = dx_make_map ((struct ext3_dir_entry_2 *) data1,
blocksize, hinfo, map);
map -= count;
dx_sort_map (map, count);
/* Split the existing block in the middle, size-wise */
size = 0;
move = 0;
for (i = count-1; i >= 0; i--) {
/* is more than half of this entry in 2nd half of the block? */
if (size + map[i].size/2 > blocksize/2) <====
You sure this isn't our old friend
https://bugzilla.redhat.com/show_bug.cgi?id=451068 ?
which version of gcc compiled this?
As we discussed on IRC, I think you're theory is dead on. %ecx is at
the very end of the page-2, which would correspond to
map[count-1].size. And size (%esi) is zero, which rules out my scenario.
This very much looks like a GCC bug. Asheesh, can you confirm which
version of GCC you used to build your kernel?
gcc --version indicates:
gcc (Debian 4.3.1-2) 4.3.1
dpkg -l gcc reports:
ii gcc 4:4.3.1-1 The GNU C compiler
Longer term, do_split() was coded in a very non-robust fashion.
Looking at do_split(), it was pretty easy to imagine corrupted
directory blocks that might force count to be 0 (causing the for loop
to do something insane, since i is unsigned), and adding some checks
to make sure that the split variable is neither 0 nor equal to count
might also be a really good idea.
Thanks for the speedy replies, all. I guess then you're not interested in
those e2image dumps I took, then.
I'm recompiling with GCC 4.2 now; is there a straightforward(ish) test
you've seen that can indicate if the GCC 4.3 in Debian unstable or Debian
testing still has this bug? FWIW their changelogs are at
http://packages.debian.org/changelogs/pool/main/g/gcc-4.3/gcc-4.3_4.3.1-8/changelog
.
-- Asheesh.
--
He is a man capable of turning any colour into grey.
-- John LeCarre
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