From 864c2357ca898c6171fe5284f5ecc795c8ce27a8 Mon Sep 17 00:00:00 2001 From: David Carrillo-Cisneros Date: Tue, 1 Nov 2016 11:52:58 -0700 Subject: 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 cycles g2 3.000589181 cycles g2 4.000771428 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 cycles g2 2.000389430 cycles g2 3.000590962 cycles g2 Signed-off-by: David Carrillo-Cisneros Signed-off-by: Peter Zijlstra (Intel) Cc: Alexander Shishkin Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Kan Liang Cc: Linus Torvalds Cc: Nilay Vaish Cc: Paul Turner Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vegard Nossum Link: http://lkml.kernel.org/r/1478026378-86083-1-git-send-email-davidcc@google.com Signed-off-by: Ingo Molnar --- kernel/events/core.c | 11 +++++++++++ 1 file changed, 11 insertions(+) (limited to 'kernel') diff --git a/kernel/events/core.c b/kernel/events/core.c index 0e292132efac..ff230bb4a02e 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; } -- cgit v1.2.3