netdev - Re: [PATCH 2/8] bitmap: Introduce bitmap_set, bitmap_clear, bitmap_find_next_zero

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Date:	Sat, 17 Oct 2009 23:51:32 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	akinobu.mita@...il.com
Cc:	fujita.tomonori@....ntt.co.jp, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, davem@...emloft.net,
	sparclinux@...r.kernel.org, benh@...nel.crashing.org,
	paulus@...ba.org, linuxppc-dev@...abs.org, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, x86@...nel.org, gregkh@...e.de,
	LW@...o-electronics.de, linux-usb@...r.kernel.org,
	rolandd@...co.com, yevgenyp@...lanox.co.il, netdev@...r.kernel.org,
	tony.luck@...el.com, fenghua.yu@...el.com,
	linux-ia64@...r.kernel.org, linux-altix@....com
Subject: Re: [PATCH 2/8] bitmap: Introduce bitmap_set, bitmap_clear, 
	bitmap_find_next_zero_area

On Sat, 17 Oct 2009 23:43:56 +0900
Akinobu Mita <akinobu.mita@...il.com> wrote:

> 2009/10/17 FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>:
> > On Tue, 13 Oct 2009 18:10:17 +0900
> > Akinobu Mita <akinobu.mita@...il.com> wrote:
> >
> >> My user space testing exposed off-by-one error find_next_zero_area
> >> in iommu-helper. Some zero area cannot be found by this bug.
> >>
> >> Subject: [PATCH] Fix off-by-one error in find_next_zero_area
> >>
> >> Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
> >> ---
> >>  lib/iommu-helper.c |    2 +-
> >>  1 files changed, 1 insertions(+), 1 deletions(-)
> >>
> >> diff --git a/lib/iommu-helper.c b/lib/iommu-helper.c
> >> index 75dbda0..afc58bc 100644
> >> --- a/lib/iommu-helper.c
> >> +++ b/lib/iommu-helper.c
> >> @@ -19,7 +19,7 @@ again:
> >>       index = (index + align_mask) & ~align_mask;
> >>
> >>       end = index + nr;
> >> -     if (end >= size)
> >> +     if (end > size)
> >
> > I think that this is intentional; the last byte of the limit doesn't
> > work.
> 
> It looks ok to me. Without above change, find_next_zero_area cannot
> find a 64 bits zeroed area in next sample code.

I meant that we don't want to find such area for IOMMUs (IIRC, it code
came from POWER IOMMU).


>         unsigned long offset;
> 
>         DECLARE_BITMAP(map, 64);
> 
>         bitmap_clear(map, 0, 64);
>         offset = find_next_zero_area(map, 64, 0, 64, 0);
>         if (offset >= 64)
>                 printf("not found\n");
>         else
>                 printf("found\n");
> --
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