[tip:perf/urgent] perf/core: Remove invalid warning from list_update_cgroup_even()t

[tip-bot for David Carrillo-Cisneros]

Commit-ID:  8fc31ce8896fc3cea1d79688c8ff950ad4e73afe
Gitweb:     http://git.kernel.org/tip/8fc31ce8896fc3cea1d79688c8ff950ad4e73afe
Author:     David Carrillo-Cisneros <davidcc@xxxxxxxxxx>
AuthorDate: Sun, 4 Dec 2016 00:46:17 -0800
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 6 Dec 2016 09:44:29 +0100

perf/core: Remove invalid warning from list_update_cgroup_even()t

The warning introduced in commit:

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

assumed that a cgroup switch always precedes list_del_event. This is
not the case. Remove warning.

Make sure that cpuctx->cgrp is NULL until a cgroup event is sched in
or ctx->nr_cgroups == 0.

Signed-off-by: David Carrillo-Cisneros <davidcc@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Kan Liang <kan.liang@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Cc: Nilay Vaish <nilayvaish@xxxxxxxxx>
Cc: Paul Turner <pjt@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ravi V Shankar <ravi.v.shankar@xxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vegard Nossum <vegard.nossum@xxxxxxxxx>
Cc: Vikas Shivappa <vikas.shivappa@xxxxxxxxxxxxxxx>
Cc: Vince Weaver <vincent.weaver@xxxxxxxxx>
Link: http://lkml.kernel.org/r/1480841177-27299-1-git-send-email-davidcc@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 kernel/events/core.c | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 6ee1feb..02c8421 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -903,17 +903,14 @@ list_update_cgroup_event(struct perf_event *event,
 	 */
 	cpuctx = __get_cpu_context(ctx);
 
-	/* Only set/clear cpuctx->cgrp if current task uses event->cgrp. */
-	if (perf_cgroup_from_task(current, ctx) != event->cgrp) {
-		/*
-		 * We are removing the last cpu event in this context.
-		 * If that event is not active in this cpu, cpuctx->cgrp
-		 * should've been cleared by perf_cgroup_switch.
-		 */
-		WARN_ON_ONCE(!add && cpuctx->cgrp);
-		return;
-	}
-	cpuctx->cgrp = add ? event->cgrp : NULL;
+	/*
+	 * cpuctx->cgrp is NULL until a cgroup event is sched in or
+	 * ctx->nr_cgroup == 0 .
+	 */
+	if (add && perf_cgroup_from_task(current, ctx) == event->cgrp)
+		cpuctx->cgrp = event->cgrp;
+	else if (!add)
+		cpuctx->cgrp = NULL;
 }
 
 #else /* !CONFIG_CGROUP_PERF */