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Message-ID: <tip-864c2357ca898c6171fe5284f5ecc795c8ce27a8@git.kernel.org>
Date: Wed, 16 Nov 2016 00:36:49 -0800
From: tip-bot for David Carrillo-Cisneros <tipbot@...or.com>
To: linux-tip-commits@...r.kernel.org
Cc: kan.liang@...el.com, jolsa@...hat.com, pjt@...gle.com,
linux-kernel@...r.kernel.org, acme@...hat.com, hpa@...or.com,
peterz@...radead.org, alexander.shishkin@...ux.intel.com,
eranian@...gle.com, torvalds@...ux-foundation.org,
nilayvaish@...il.com, vegard.nossum@...il.com, mingo@...nel.org,
tglx@...utronix.de, davidcc@...gle.com
Subject: [tip:perf/urgent] perf/core: Do not set cpuctx->cgrp for
unscheduled cgroups
Commit-ID: 864c2357ca898c6171fe5284f5ecc795c8ce27a8
Gitweb: http://git.kernel.org/tip/864c2357ca898c6171fe5284f5ecc795c8ce27a8
Author: David Carrillo-Cisneros <davidcc@...gle.com>
AuthorDate: Tue, 1 Nov 2016 11:52:58 -0700
Committer: Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 15 Nov 2016 14:18:22 +0100
perf/core: Do not set cpuctx->cgrp for unscheduled cgroups
Commit:
db4a835601b7 ("perf/core: Set cgroup in CPU contexts for new cgroup events")
failed to verify that event->cgrp is actually the scheduled cgroup
in a CPU before setting cpuctx->cgrp. This patch fixes that.
Now that there is a different path for scheduled and unscheduled
cgroup, add a warning to catch when cpuctx->cgrp is still set after
the last cgroup event has been unsheduled.
To verify the bug:
# Create 2 cgroups.
mkdir /dev/cgroups/devices/g1
mkdir /dev/cgroups/devices/g2
# launch a task, bind it to a cpu and move it to g1
CPU=2
while :; do : ; done &
P=$!
taskset -pc $CPU $P
echo $P > /dev/cgroups/devices/g1/tasks
# monitor g2 (it runs no tasks) and observe output
perf stat -e cycles -I 1000 -C $CPU -G g2
# time counts unit events
1.000091408 7,579,527 cycles g2
2.000350111 <not counted> cycles g2
3.000589181 <not counted> cycles g2
4.000771428 <not counted> cycles g2
# note first line that displays that a task run in g2, despite
# g2 having no tasks. This is because cpuctx->cgrp was wrongly
# set when context of new event was installed.
# After applying the fix we obtain the right output:
perf stat -e cycles -I 1000 -C $CPU -G g2
# time counts unit events
1.000119615 <not counted> cycles g2
2.000389430 <not counted> cycles g2
3.000590962 <not counted> cycles g2
Signed-off-by: David Carrillo-Cisneros <davidcc@...gle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Kan Liang <kan.liang@...el.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Nilay Vaish <nilayvaish@...il.com>
Cc: Paul Turner <pjt@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Stephane Eranian <eranian@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Vegard Nossum <vegard.nossum@...il.com>
Link: http://lkml.kernel.org/r/1478026378-86083-1-git-send-email-davidcc@google.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
kernel/events/core.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 0e29213..ff230bb 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -902,6 +902,17 @@ list_update_cgroup_event(struct perf_event *event,
* this will always be called from the right CPU.
*/
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;
}
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