From: Jaswinder Singh Rajput <jaswinder@kernel.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Joerg Roedel <joerg.roedel@amd.com>
Subject: Re: [PATCH] dma-debug: Fix the overlap() function to be correct and readable
Date: Tue, 14 Jul 2009 16:22:15 +0530 [thread overview]
Message-ID: <1247568735.2473.26.camel@ht.satnam> (raw)
In-Reply-To: <1247567822.2473.21.camel@ht.satnam>
On Tue, 2009-07-14 at 16:07 +0530, Jaswinder Singh Rajput wrote:
> On Tue, 2009-07-14 at 15:45 +0530, Jaswinder Singh Rajput wrote:
> > > >From 35c89da82e969a2fd157478940e7ecde1e19ccc4 Mon Sep 17 00:00:00 2001
> > > From: Ingo Molnar <mingo@elte.hu>
> > > Date: Fri, 10 Jul 2009 21:38:02 +0200
> > > Subject: [PATCH] dma-debug: Fix the overlap() function to be correct and readable
> > >
> > > Linus noticed how unclean and buggy the overlap() function is:
> > >
> > > - It uses convoluted (and bug-causing) positive checks for
> > > range overlap - instead of using a more natural negative
> > > check.
> > >
> > > - Even the positive checks are buggy: a positive intersection
> > > check has four natural cases while we checked only for three,
> > > missing the (addr < start && addr2 == end) case for example.
> > >
> > > - The variables are mis-named, making it non-obvious how the
> > > check was done.
> > >
> > > - It needlessly uses u64 instead of unsigned long. Since these
> > > are kernel memory pointers and we explicitly exclude highmem
> > > ranges anyway we cannot ever overflow 32 bits, even if we
> > > could. (and on 64-bit it doesnt matter anyway)
> > >
> > > All in one, this function needs a total revamp. I used Linus's
> > > suggestions minus the paranoid checks (we cannot overflow really
> > > because if we get totally bad DMA ranges passed far more things
> > > break in the systems than just DMA debugging). I also fixed a
> > > few other small details i noticed.
> > >
> > > Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
> > > Cc: Joerg Roedel <joerg.roedel@amd.com>
> > > Signed-off-by: Ingo Molnar <mingo@elte.hu>
> > > ---
> > > lib/dma-debug.c | 24 ++++++++++++------------
> > > 1 files changed, 12 insertions(+), 12 deletions(-)
> > >
> > > diff --git a/lib/dma-debug.c b/lib/dma-debug.c
> > > index c9187fe..02fed52 100644
> > > --- a/lib/dma-debug.c
> > > +++ b/lib/dma-debug.c
> > > @@ -856,22 +856,21 @@ static void check_for_stack(struct device *dev, void *addr)
> > > "stack [addr=%p]\n", addr);
> > > }
> > >
> > > -static inline bool overlap(void *addr, u64 size, void *start, void *end)
> > > +static inline bool overlap(void *addr, unsigned long len, void *start, void *end)
> > > {
> > > - void *addr2 = (char *)addr + size;
> > > + unsigned long a1 = (unsigned long)addr;
> > > + unsigned long b1 = a1 + len;
> > > + unsigned long a2 = (unsigned long)start;
> > > + unsigned long b2 = (unsigned long)end;
> > >
> > > - return ((addr >= start && addr < end) ||
> > > - (addr2 >= start && addr2 < end) ||
> > > - ((addr < start) && (addr2 > end)));
> > > + return !(b1 <= a2 || a1 >= b2);
> > > }
> > >
> >
> > If b1 = a2 (overlap) then this function will say 0
> > If a1 = b2 (overlap) then this function will say 0
> >
> > if b1 > (a2 + infinite) which is not overlap this function will say 1
> >
> > I think we need to test both edges.
> >
> > So it should be :
> >
> > return ((a2 <= b1 && b2 >= a1) || (a1 <= b2 && a2 <= b1));
> >
>
> We can make it more beautiful like :
>
> return ((a2 <= b1 && b2 >= a1) || (a1 <= b2 && b1 >= a2));
>
In above case I tested overlapping on both side : left and right.
but result is same so (x || x) = x, so in simplified version we can
write :
return a1 <= b2 && b1 >= a2;
Thanks,
--
JSR
next prev parent reply other threads:[~2009-07-14 10:53 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-07-10 16:28 [GIT PULL] core kernel fixes Ingo Molnar
2009-07-10 19:06 ` Linus Torvalds
2009-07-10 19:31 ` Ingo Molnar
2009-07-10 19:51 ` [PATCH] dma-debug: Fix the overlap() function to be correct and readable Ingo Molnar
2009-07-10 20:07 ` Linus Torvalds
2009-07-10 20:34 ` Ingo Molnar
2009-07-14 10:15 ` Jaswinder Singh Rajput
2009-07-14 10:37 ` Jaswinder Singh Rajput
2009-07-14 10:52 ` Jaswinder Singh Rajput [this message]
2009-07-10 19:52 ` [GIT PULL] core kernel fixes Linus Torvalds
2009-07-10 20:02 ` Ingo Molnar
2009-07-10 20:36 ` [GIT PULL, v2] " Ingo Molnar
2009-07-13 14:52 ` [GIT PULL] " Joerg Roedel
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