linux-kernel - [tip:perf/urgent] perf/cgroup: Fix perf cgroup hierarchy support

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Date:   Mon, 30 Oct 2017 04:26:03 -0700
From:   tip-bot for Tejun Heo <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org, acme@...nel.org,
        peterz@...radead.org, davidcc@...gle.com,
        torvalds@...ux-foundation.org, tglx@...utronix.de, tj@...nel.org,
        hpa@...or.com
Subject: [tip:perf/urgent] perf/cgroup: Fix perf cgroup hierarchy support

Commit-ID:  be96b316deff35e119760982c43af74e606fa143
Gitweb:     https://git.kernel.org/tip/be96b316deff35e119760982c43af74e606fa143
Author:     Tejun Heo <tj@...nel.org>
AuthorDate: Sat, 28 Oct 2017 09:49:37 -0700
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Mon, 30 Oct 2017 11:58:51 +0100

perf/cgroup: Fix perf cgroup hierarchy support

The following commit:

  864c2357ca89 ("perf/core: Do not set cpuctx->cgrp for unscheduled cgroups")

made list_update_cgroup_event() skip setting cpuctx->cgrp if no cgroup event
targets %current's cgroup.

This breaks perf_event's hierarchical support because events which target one
of the ancestors get ignored.

Fix it by using cgroup_is_descendant() test instead of equality.

Signed-off-by: Tejun Heo <tj@...nel.org>
Acked-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: David Carrillo-Cisneros <davidcc@...gle.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: kernel-team@...com
Cc: stable@...r.kernel.org # v4.9+
Fixes: 864c2357ca89 ("perf/core: Do not set cpuctx->cgrp for unscheduled cgroups")
Link: http://lkml.kernel.org/r/20171028164237.GA972780@devbig577.frc2.facebook.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/events/core.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 9d93db8..10cdb9c 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -901,9 +901,11 @@ list_update_cgroup_event(struct perf_event *event,
 	cpuctx_entry = &cpuctx->cgrp_cpuctx_entry;
 	/* cpuctx->cgrp is NULL unless a cgroup event is active in this CPU .*/
 	if (add) {
+		struct perf_cgroup *cgrp = perf_cgroup_from_task(current, ctx);
+
 		list_add(cpuctx_entry, this_cpu_ptr(&cgrp_cpuctx_list));
-		if (perf_cgroup_from_task(current, ctx) == event->cgrp)
-			cpuctx->cgrp = event->cgrp;
+		if (cgroup_is_descendant(cgrp->css.cgroup, event->cgrp->css.cgroup))
+			cpuctx->cgrp = cgrp;
 	} else {
 		list_del(cpuctx_entry);
 		cpuctx->cgrp = NULL;