Re: [PATCH -v3] x86: do not free zero sized per cpu areas

[Ian Campbell]

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@xxxxxxxxxx>
> >>
> >> 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@xxxxxxxxxx>
> >> Signed-off-by: Yinghai Lu <yinghai@xxxxxxxxxx>
> >> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> >> Cc: Ingo Molnar <mingo@xxxxxxx>
> >> ---
> >>  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@xxxxxxxxxx>
> 
> 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@xxxxxxxxxx>
> Signed-off-by: Yinghai Lu <yinghai@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxx>
> ---
>  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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