linux-kernel - Re: 2.6.24-rc6-mm1

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Message-Id: <20080107151639P.fujita.tomonori@lab.ntt.co.jp>
Date:	Mon, 07 Jan 2008 15:16:39 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	just.for.lkml@...glemail.com
Cc:	tomof@....org, akpm@...ux-foundation.org, jarkao2@...il.com,
	herbert@...dor.apana.org.au, linux-kernel@...r.kernel.org,
	neilb@...e.de, bfields@...ldses.org, netdev@...r.kernel.org,
	tom@...ngridcomputing.com, fujita.tomonori@....ntt.co.jp
Subject: Re: 2.6.24-rc6-mm1

On Sun, 6 Jan 2008 21:03:42 +0100
"Torsten Kaiser" <just.for.lkml@...glemail.com> wrote:

> On Jan 6, 2008 2:33 PM, FUJITA Tomonori <tomof@....org> wrote:
> > On Sun, 6 Jan 2008 12:35:35 +0100
> > "Torsten Kaiser" <just.for.lkml@...glemail.com> wrote:
> > > On Jan 6, 2008 12:23 PM, FUJITA Tomonori <tomof@....org> wrote:
> > > > On Sun, 6 Jan 2008 11:41:10 +0100
> > > > "Torsten Kaiser" <just.for.lkml@...glemail.com> wrote:
> > > > > I will applie your patch and see if this hunk from
> > > > > find_next_zero_area() makes a difference:
> > > > >
> > > > >        end = index + nr;
> > > > > -       if (end > size)
> > > > > +       if (end >= size)
> > > > >                 return -1;
> 
> -> that might still have made a difference, but ...
> 
> > > > > -       for (i = index + 1; i < end; i++) {
> > > > > +       for (i = index; i < end; i++) {
> 
> ... as you say below, the test for the index position is only needed
> if index is modified after find_next_zero_bit().
> 
> > > > >                 if (test_bit(i, map)) {
> > > >
> > > > The patch should not make a difference for X86_64.
> > >
> > > Hmm...
> > > arch/x86/kernel/pci-gart_64.c:
> > > alloc_iommu() calls iommu_area_alloc()
> > > lib/iommu-helper.c:
> > > iommu_area_alloc() calls find_next_zero_area()
> > > -> so the above code should be called even on X86_64
> >
> > Oops, I meant that the patch fixes the align allocation (non zero
> > align_mask case). X86_64 doesn't use the align allocation.
> >
> >
> > > And the change in the for loop means that 'index' will now be tested,
> > > but with the old code it was not.
> >
> > With the old code, 'index' is tested by find_next_zero_bit.
> >
> > With the new code and non zero align_mask case, 'index' is not tested
> > by find_next_zero_bit. So test_bit needs to start with 'index'.
> >
> > So If I understand the correctly, this patch should not make a
> > difference for x86_64 though I might miss something.
> 
> You did not miss anything.
> After 18 packages my system crashed again.
> 
> > > And double using something does fit with the errors I'm seeing...
> > >
> > > > Can you try the patch to revert my IOMMU changes?
> > > >
> > > > http://www.mail-archive.com/linux-scsi@vger.kernel.org/msg12694.html
> > >
> > > Testing for this bug is a little bit slow, as I'm compiling ~100
> > > packages trying to trigger it.
> > > If my current testrun with the patch from
> > > http://www.mail-archive.com/linux-scsi@vger.kernel.org/msg12702.html
> > > crashes, I will revert the hole IOMMU changes with above patch and try again.
> >
> > Thanks for testing,
> 
> OK, I'm still testing this, but after 95 completed packages I'm rather
> certain that reverting the IOMMU changes with this patch fixes my
> problem.
> I didn't have time to look more into this, so I can't offer any
> concrete ideas where the bug is.
> 
> If you send more patches, I'm willing to test them, but it might take
> some more time during the next week.

Can you try 2.6.24-rc7 + the IOMMU changes?

The patches are available at:

http://www.kernel.org/pub/linux/kernel/people/tomo/iommu/

Or if you prefer the git tree:

git://git.kernel.org/pub/scm/linux/kernel/git/tomo/linux-2.6-misc.git iommu-sg-fixes



I've looked at the changes to GART but they are straightforward and
don't look wrong...


Thanks,
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