linux-kernel - Re: [patch] slob: fix memory corruption

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Message-Id: <200711160725.13067.nickpiggin@yahoo.com.au>
Date:	Fri, 16 Nov 2007 07:25:12 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	David Miller <davem@...emloft.net>, mpm@...enic.com, rjw@...k.pl,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch] slob: fix memory corruption

On Thursday 15 November 2007 23:48, Ingo Molnar wrote:
> > From: Nick Piggin <npiggin@...e.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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