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From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Ingo Molnar <mingo@elte.hu>
Subject: Re: [patch] slob: fix memory corruption
Date: Fri, 16 Nov 2007 07:25:12 +1100
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Cc: David Miller <davem@davemloft.net>, mpm@selenic.com, rjw@sisk.pl,
       linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
       torvalds@linux-foundation.org, Thomas Gleixner <tglx@linutronix.de>
References: <20071114225335.GV19691@waste.org> <20071115113204.GA24463@elte.hu> <20071115124844.GA6606@elte.hu>
In-Reply-To: <20071115124844.GA6606@elte.hu>
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On Thursday 15 November 2007 23:48, Ingo Molnar wrote:
> > From: Nick Piggin <npiggin@suse.de>
> >
> > -		if (free_slob_pages.next != prev->next)
> > +		if (prev != free_slob_pages.prev &&
> > +				free_slob_pages.next != prev->next)
> >  			list_move_tail(&free_slob_pages, prev->next);
>
> btw., exactly how did you find this bug? User-space simulation of SLOB?

Yes. It was very useful in developing the improvements to the freelist
handling. The only reason why I don't release/run the code more often
is that my test harness work is pretty ugly (ie. it isn't just a simple
cp mm/slob.c ../blah/).

After that, just a loop of N iterations, within each iteration, there is
a chance of a single allocation of a random size, a single free of a
random outstanding allocation, a run of allocating MAX allocations, or
a run of freeing all previously allocated memory. It's a bit crude, but
it showed up your list head corruption in a second or two.
-
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