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Subject[PATCH 4.14 272/496] perf/cgroup: Fix child event counting bug
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

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

From: Song Liu <songliubraving@fb.com>

[ 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@fb.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <jolsa@redhat.com>
Cc: <kernel-team@fb.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Link: http://lkml.kernel.org/r/20180312165943.1057894-1-songliubraving@fb.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/events/core.c | 21 ++++++++++++++++-----
1 file changed, 16 insertions(+), 5 deletions(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -642,9 +642,15 @@ 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)
@@ -672,6 +678,7 @@ 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
@@ -682,8 +689,12 @@ 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;
+ }
}

static DEFINE_PER_CPU(struct list_head, cgrp_cpuctx_list);

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