Messages in this thread Patch in this message | | | Date | Wed, 16 Nov 2016 00:36:49 -0800 | From | tip-bot for David Carrillo-Cisneros <> | Subject | [tip:perf/urgent] perf/core: Do not set cpuctx->cgrp for unscheduled cgroups |
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Commit-ID: 864c2357ca898c6171fe5284f5ecc795c8ce27a8 Gitweb: http://git.kernel.org/tip/864c2357ca898c6171fe5284f5ecc795c8ce27a8 Author: David Carrillo-Cisneros <davidcc@google.com> AuthorDate: Tue, 1 Nov 2016 11:52:58 -0700 Committer: Ingo Molnar <mingo@kernel.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@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Kan Liang <kan.liang@intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Nilay Vaish <nilayvaish@gmail.com> Cc: Paul Turner <pjt@google.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Stephane Eranian <eranian@google.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vegard Nossum <vegard.nossum@gmail.com> Link: http://lkml.kernel.org/r/1478026378-86083-1-git-send-email-davidcc@google.com Signed-off-by: Ingo Molnar <mingo@kernel.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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