[PATCH 4.9 206/329] perf/cgroup: Fix child event counting bug

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Song Liu <songliubraving@xxxxxx>

[ Upstream commit c917e0f259908e75bd2a65877e25f9d90c22c848 ]

When a perf_event is attached to parent cgroup, it should count events
for all children cgroups:

   parent_group   <---- perf_event
     \
      - child_group  <---- process(es)

However, in our tests, we found this perf_event cannot report reliable
results. Here is an example case:

  # create cgroups
  mkdir -p /sys/fs/cgroup/p/c
  # start perf for parent group
  perf stat -e instructions -G "p"

  # on another console, run test process in child cgroup:
  stressapptest -s 2 -M 1000 & echo $! > /sys/fs/cgroup/p/c/cgroup.procs

  # after the test process is done, stop perf in the first console shows

       <not counted>      instructions              p

The instruction should not be "not counted" as the process runs in the
child cgroup.

We found this is because perf_event->cgrp and cpuctx->cgrp are not
identical, thus perf_event->cgrp are not updated properly.

This patch fixes this by updating perf_cgroup properly for ancestor
cgroup(s).

Reported-by: Ephraim Park <ephiepark@xxxxxx>
Signed-off-by: Song Liu <songliubraving@xxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: <jolsa@xxxxxxxxxx>
Cc: <kernel-team@xxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vince Weaver <vincent.weaver@xxxxxxxxx>
Link: http://lkml.kernel.org/r/20180312165943.1057894-1-songliubraving@xxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 kernel/events/core.c |   21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -634,9 +634,15 @@ static inline void __update_cgrp_time(st
 
 static inline void update_cgrp_time_from_cpuctx(struct perf_cpu_context *cpuctx)
 {
-	struct perf_cgroup *cgrp_out = cpuctx->cgrp;
-	if (cgrp_out)
-		__update_cgrp_time(cgrp_out);
+	struct perf_cgroup *cgrp = cpuctx->cgrp;
+	struct cgroup_subsys_state *css;
+
+	if (cgrp) {
+		for (css = &cgrp->css; css; css = css->parent) {
+			cgrp = container_of(css, struct perf_cgroup, css);
+			__update_cgrp_time(cgrp);
+		}
+	}
 }
 
 static inline void update_cgrp_time_from_event(struct perf_event *event)
@@ -664,6 +670,7 @@ perf_cgroup_set_timestamp(struct task_st
 {
 	struct perf_cgroup *cgrp;
 	struct perf_cgroup_info *info;
+	struct cgroup_subsys_state *css;
 
 	/*
 	 * ctx->lock held by caller
@@ -674,8 +681,12 @@ perf_cgroup_set_timestamp(struct task_st
 		return;
 
 	cgrp = perf_cgroup_from_task(task, ctx);
-	info = this_cpu_ptr(cgrp->info);
-	info->timestamp = ctx->timestamp;
+
+	for (css = &cgrp->css; css; css = css->parent) {
+		cgrp = container_of(css, struct perf_cgroup, css);
+		info = this_cpu_ptr(cgrp->info);
+		info->timestamp = ctx->timestamp;
+	}
 }
 
 #define PERF_CGROUP_SWOUT	0x1 /* cgroup switch out every event */