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Commit c3c87e77 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
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perf: Tighten (and fix) the grouping condition 



The fix from 9fc81d87 ("perf: Fix events installation during
moving group") was incomplete in that it failed to recognise that
creating a group with events for different CPUs is semantically
broken -- they cannot be co-scheduled.

Furthermore, it leads to real breakage where, when we create an event
for CPU Y and then migrate it to form a group on CPU X, the code gets
confused where the counter is programmed -- triggered in practice
as well by me via the perf fuzzer.

Fix this by tightening the rules for creating groups. Only allow
grouping of counters that can be co-scheduled in the same context.
This means for the same task and/or the same cpu.

Fixes: 9fc81d87 ("perf: Fix events installation during moving group")
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20150123125834.090683288@infradead.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent ef454cae

include/linux/perf_event.h

+0 −6
Original line number Diff line number Diff line
@@ -450,11 +450,6 @@ struct perf_event { 
#endif /* CONFIG_PERF_EVENTS */

};



enum perf_event_context_type {

	task_context,

	cpu_context,

};



/**

 * struct perf_event_context - event context structure

 *
@@ -462,7 +457,6 @@ enum perf_event_context_type { 
 */

struct perf_event_context {

	struct pmu			*pmu;

	enum perf_event_context_type	type;

	/*

	 * Protect the states of the events in the list,

	 * nr_active, and the list:

kernel/events/core.c

+13 −2
Original line number Diff line number Diff line
@@ -6776,7 +6776,6 @@ int perf_pmu_register(struct pmu *pmu, const char *name, int type) 
		__perf_event_init_context(&cpuctx->ctx);

		lockdep_set_class(&cpuctx->ctx.mutex, &cpuctx_mutex);

		lockdep_set_class(&cpuctx->ctx.lock, &cpuctx_lock);

		cpuctx->ctx.type = cpu_context;

		cpuctx->ctx.pmu = pmu;



		__perf_cpu_hrtimer_init(cpuctx, cpu);
@@ -7420,7 +7419,19 @@ SYSCALL_DEFINE5(perf_event_open, 
		 * task or CPU context:

		 */

		if (move_group) {

			if (group_leader->ctx->type != ctx->type)

			/*

			 * Make sure we're both on the same task, or both

			 * per-cpu events.

			 */

			if (group_leader->ctx->task != ctx->task)

				goto err_context;



			/*

			 * Make sure we're both events for the same CPU;

			 * grouping events for different CPUs is broken; since

			 * you can never concurrently schedule them anyhow.

			 */

			if (group_leader->cpu != event->cpu)

				goto err_context;

		} else {

			if (group_leader->ctx != ctx)