[PATCH 3.18 39/68] perf: Tighten (and fix) the grouping condition

Greg Kroah-Hartman
2017-05-05T18:49:16Z

From: Peter Zijlstra <peterz@infradead.org>

commit c3c87e770458aa004bd7ed3f29945ff436fd6511 upstream.

The fix from 9fc81d87420d ("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: 9fc81d87420d ("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>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/linux/perf_event.h | 6 ------
kernel/events/core.c | 15 +++++++++++++--
2 files changed, 13 insertions(+), 8 deletions(-)

--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -455,11 +455,6 @@ struct perf_event {
#endif /* CONFIG_PERF_EVENTS */
};

-enum perf_event_context_type {
- task_context,
- cpu_context,
-};
-
/**
* struct perf_event_context - event context structure
*
@@ -467,7 +462,6 @@ 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:
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6803,7 +6803,6 @@ 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);
@@ -7445,7 +7444,19 @@ 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)