hi,
any feedback?
thanks,
jirka
On Wed, Jun 25, 2014 at 08:44:35PM +0200, Jiri Olsa wrote:
> From: Jiri Olsa <jo...@redhat.com>
>
> While iterating siblings in perf_output_read_group we could
> race with addition and removal of sibling in perf_group_attach
> and perf_group_detach respective.
>
> While in perf_output_read_group we are under active context,
> so the only sibling_list modification could come via IPI in:
> perf_install_in_context or perf_remove_from_context
>
> Disable interrupts before iterating siblings to prevent
> this race.
>
> Cc: Arnaldo Carvalho de Melo <a...@kernel.org>
> Cc: Corey Ashford <cjash...@linux.vnet.ibm.com>
> Cc: Frederic Weisbecker <fweis...@gmail.com>
> Cc: Ingo Molnar <mi...@kernel.org>
> Cc: Paul Mackerras <pau...@samba.org>
> Cc: Peter Zijlstra <a.p.zijls...@chello.nl>
> Signed-off-by: Jiri Olsa <jo...@kernel.org>
> ---
> kernel/events/core.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index a33d9a2b..66649d3 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -4509,6 +4509,7 @@ static void perf_output_read_group(struct
> perf_output_handle *handle,
> {
> struct perf_event *leader = event->group_leader, *sub;
> u64 read_format = event->attr.read_format;
> + unsigned long flags;
> u64 values[5];
> int n = 0;
>
> @@ -4529,6 +4530,15 @@ static void perf_output_read_group(struct
> perf_output_handle *handle,
>
> __output_copy(handle, values, n * sizeof(u64));
>
> + /*
> + * We are now under active context, so the only sibling_list
> + * modification could come via IPI in:
> + * perf_install_in_context and perf_remove_from_context
> + *
> + * Disable interrupts to prevent this race.
> + */
> + local_irq_save(flags);
> +
> list_for_each_entry(sub, &leader->sibling_list, group_entry) {
> n = 0;
>
> @@ -4542,6 +4552,7 @@ static void perf_output_read_group(struct
> perf_output_handle *handle,
>
> __output_copy(handle, values, n * sizeof(u64));
> }
> + local_irq_restore(flags);
> }
>
> #define PERF_FORMAT_TOTAL_TIMES (PERF_FORMAT_TOTAL_TIME_ENABLED|\
> --
> 1.8.3.1
>
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