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SubjectRe: [PATCH] Fix infinite loop in ARM user perf_event backtrace code
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Hi Sonny,

On Sat, 2011-04-16 at 04:27 +0100, Sonny Rao wrote:
> The ARM user backtrace code can get into an infinite loop if it
> runs into an invalid stack frame which points back to itself.
> This situation has been observed in practice. Fix it by capping
> the number of entries in the backtrace. This is also what other
> architectures do in their backtrace code.
>
> Signed-off-by: Sonny Rao <sonnyrao@chromium.org>
> ---
> arch/arm/kernel/perf_event.c | 3 ++-
> 1 files changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c
> index 69cfee0..1e61d60 100644
> --- a/arch/arm/kernel/perf_event.c
> +++ b/arch/arm/kernel/perf_event.c
> @@ -746,7 +746,8 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs)
>
> tail = (struct frame_tail __user *)regs->ARM_fp - 1;
>
> - while (tail && !((unsigned long)tail & 0x3))
> + while ((entry->nr < PERF_MAX_STACK_DEPTH) &&
> + tail && !((unsigned long)tail & 0x3))
> tail = user_backtrace(tail, entry);
> }

Ok. Please can you put this into Russell's patch system?

Will



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