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Commit c44d70a3 authored by Ingo Molnar's avatar Ingo Molnar
Browse files

perf_counter: fix counter inheritance race 



Context rotation should not occur when we are in the middle of
walking the counter list when inheriting counters ...

[ Impact: fix occasionally incorrect perf stat results ]

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 33b2fb30

include/linux/perf_counter.h

+1 −0
Original line number Diff line number Diff line
@@ -508,6 +508,7 @@ struct perf_counter_context { 
	int			nr_counters;

	int			nr_active;

	int			is_active;

	int			rr_allowed;

	struct task_struct	*task;



	/*

kernel/perf_counter.c

+9 −1
Original line number Diff line number Diff line
@@ -1120,6 +1120,7 @@ void perf_counter_task_tick(struct task_struct *curr, int cpu) 
	__perf_counter_task_sched_out(ctx);



	rotate_ctx(&cpuctx->ctx);

	if (ctx->rr_allowed)

		rotate_ctx(ctx);



	perf_counter_cpu_sched_in(cpuctx, cpu);
@@ -3108,6 +3109,7 @@ __perf_counter_init_context(struct perf_counter_context *ctx, 
	mutex_init(&ctx->mutex);

	INIT_LIST_HEAD(&ctx->counter_list);

	INIT_LIST_HEAD(&ctx->event_list);

	ctx->rr_allowed = 1;

	ctx->task = task;

}
@@ -3348,6 +3350,9 @@ void perf_counter_init_task(struct task_struct *child) 
	 */

	mutex_lock(&parent_ctx->mutex);



	parent_ctx->rr_allowed = 0;

	barrier(); /* irqs */



	/*

	 * We dont have to disable NMIs - we are only looking at

	 * the list, not manipulating it:
@@ -3361,6 +3366,9 @@ void perf_counter_init_task(struct task_struct *child) 
			break;

	}



	barrier(); /* irqs */

	parent_ctx->rr_allowed = 1;



	mutex_unlock(&parent_ctx->mutex);

}