perf: Tighten (and fix) the grouping condition (c3c87e77) · Commits · 戴 / test

The fix from ("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: ("perf: Fix events installation during moving group") Signed-off-by:

Peter 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:

Ingo Molnar <mingo@kernel.org>

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 @@ skip_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)

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