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SubjectRe: [PATCH -v3] x86: do not free zero sized per cpu areas
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On Fri, 2010-03-19 at 23:24 +0000, Yinghai Lu wrote: 
> On 03/19/2010 03:21 PM, H. Peter Anvin wrote:
> > On 03/19/2010 03:18 PM, Yinghai Lu wrote:
> >> From: Ian Campbell <ian.campbell@citrix.com>
> >> This avoids an infinite loop in free_early_partial().
> >>
> >> Add a warning to free_early_partial to catch future problems.
> >>
> >> -v3: according to hpa, don't bother caller.
> >>
> >> Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
> >> Signed-off-by: Yinghai Lu <yinghai@kernel.org>
> >> Cc: Peter Zijlstra <peterz@infradead.org>
> >> Cc: Ingo Molnar <mingo@elte.hu>
> >> ---
> >> kernel/early_res.c | 5 +++++
> >> 1 files changed, 5 insertions(+), 0 deletions(-)
> >>
> >> diff --git a/kernel/early_res.c b/kernel/early_res.c
> >> index 3cb2c66..f3a861b 100644
> >> --- a/kernel/early_res.c
> >> +++ b/kernel/early_res.c
> >> @@ -333,6 +333,11 @@ void __init free_early_partial(u64 start, u64 end)
> >> struct early_res *r;
> >> int i;
> >>
> >> + if (WARN_ONCE(start >= end,
> >> + "free_early_partial got wrong start/end %#llx/%#llx\n",
> >> + start, end))
> >> + return;
> >> +
> >> try_next:
> >> i = find_overlapped_early(start, end);
> >> if (i >= max_early_res)
> >
> > No, that's wrong.
> >
> > The workaround is still needed for the case of equality to avoid the
> > infinite loop.
> >
> > So you need an:
> >
> > if (start == end)
> > return;
> >
>
> confused, do you mean like this
> if (start < end), find_overlapped_early will stop the loop.

I think Peter means:

if (start == end)
return;
if (WARN_ONCE(start < end, "blah"))
return;
i.e. silently ignore a zero sized region and verbosely ignore a
negatively sized one.

Ian.


> From: Ian Campbell <ian.campbell@citrix.com>
>
> This avoids an infinite loop in free_early_partial().
>
> Add a warning to free_early_partial to catch future problems.
>
> -v3: according to hpa, don't bother caller.
>
> Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
> Signed-off-by: Yinghai Lu <yinghai@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@elte.hu>
> ---
> kernel/early_res.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> Index: linux-2.6/kernel/early_res.c
> ===================================================================
> --- linux-2.6.orig/kernel/early_res.c
> +++ linux-2.6/kernel/early_res.c
> @@ -333,6 +333,14 @@ void __init free_early_partial(u64 start
> struct early_res *r;
> int i;
>
> + if (start >= end) {
> + WARN_ONCE(1,
> + "free_early_partial got wrong start/end %#llx/%#llx\n",
> + start, end);
> +
> + return;
> + }
> +
> try_next:
> i = find_overlapped_early(start, end);
> if (i >= max_early_res)




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