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SubjectRe: [PATCH] kmmio/mmiotrace: fix double free of kmmio_fault_pages
On Sat, 5 Jun 2010 21:33:01 +0200
Marcin Slusarz <marcin.slusarz@gmail.com> wrote:

> On Sat, Jun 05, 2010 at 06:49:42PM +0200, Marcin Slusarz wrote:
> > After every iounmap mmiotrace has to free kmmio_fault_pages,
> > but it can't do it directly, so it defers freeing by RCU.
> >
> > It usually works, but when mmiotraced code calls ioremap-iounmap
> > multiple times without sleeping between (so RCU won't kick in
> > and start freeing) it can be given the same virtual address, so
> > at every iounmap mmiotrace will schedule the same pages for
> > release. Obviously it will explode on second free.
> >
> > Fix it by marking kmmio_fault_pages which are scheduled for
> > release and not adding them second time.
> >
>
> Attached patch for mmiotrace testing module allows to reliably
> reproduce the bug. It can be folded into the main patch.
>
> ---
> diff --git a/arch/x86/mm/testmmiotrace.c
> b/arch/x86/mm/testmmiotrace.c index 8565d94..5f0937b 100644
> --- a/arch/x86/mm/testmmiotrace.c
> +++ b/arch/x86/mm/testmmiotrace.c
> @@ -90,6 +90,19 @@ static void do_test(unsigned long size)
> iounmap(p);
> }
>
> +static void do_test2(void)
> +{
> + void __iomem *p;
> + int i;
> +
> + for (i = 0; i < 10; ++i) {
> + p = ioremap_nocache(mmio_address, 4096);
> + if (p)
> + iounmap(p);
> + }
> + synchronize_rcu(); /* will freeing work? */
> +}
> +
> static int __init init(void)
> {
> unsigned long size = (read_far) ? (8 << 20) : (16 << 10);
> @@ -104,6 +117,7 @@ static int __init init(void)
> "and writing 16 kB of rubbish in there.\n",
> size >> 10, mmio_address);
> do_test(size);
> + do_test2();
> pr_info("All done.\n");
> return 0;
> }

Acked-by: Pekka Paalanen <pq@iki.fi>

--
Pekka Paalanen
http://www.iki.fi/pq/


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