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perf: Tighten (and fix) the grouping condition

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The fix from 9fc81d8742 ("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: 9fc81d8742 ("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>
This commit is contained in:
Peter Zijlstra 2015-01-23 11:19:48 +01:00 committed by Ingo Molnar
parent ef454caeb7
commit c3c87e7704
2 changed files with 13 additions and 8 deletions
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6
include/linux/perf_event.h
View File

@ -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:

15
kernel/events/core.c
View File

@ -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)