linux-kernel - Re: 2.6.24-rc6-mm1

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Message-ID: <64bb37e0801061203l503f29f0hd922a1347f8169ac@mail.gmail.com>
Date:	Sun, 6 Jan 2008 21:03:42 +0100
From:	"Torsten Kaiser" <just.for.lkml@...glemail.com>
To:	"FUJITA Tomonori" <tomof@....org>
Cc:	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 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.

Thanks for looking into this.

Torsten
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