perf/cgroup: Fix child event counting bug

[ Upstream commit c917e0f259908e75bd2a65877e25f9d90c22c848 ]

When a perf_event is attached to parent cgroup, it should count events
for all children cgroups:

   parent_group   <---- perf_event
     \
      - child_group  <---- process(es)

However, in our tests, we found this perf_event cannot report reliable
results. Here is an example case:

  # create cgroups
  mkdir -p /sys/fs/cgroup/p/c
  # start perf for parent group
  perf stat -e instructions -G "p"

  # on another console, run test process in child cgroup:
  stressapptest -s 2 -M 1000 & echo $! > /sys/fs/cgroup/p/c/cgroup.procs

  # after the test process is done, stop perf in the first console shows

       <not counted>      instructions              p

The instruction should not be "not counted" as the process runs in the
child cgroup.

We found this is because perf_event->cgrp and cpuctx->cgrp are not
identical, thus perf_event->cgrp are not updated properly.

This patch fixes this by updating perf_cgroup properly for ancestor
cgroup(s).

Reported-by: Ephraim Park <ephiepark@fb.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <jolsa@redhat.com>
Cc: <kernel-team@fb.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Link: http://lkml.kernel.org/r/20180312165943.1057894-1-songliubraving@fb.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 92d1f12..06bb884 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -419,9 +419,15 @@ static inline void __update_cgrp_time(struct perf_cgroup *cgrp)
 
 static inline void update_cgrp_time_from_cpuctx(struct perf_cpu_context *cpuctx)
 {
-       struct perf_cgroup *cgrp_out = cpuctx->cgrp;
-       if (cgrp_out)
-               __update_cgrp_time(cgrp_out);
+       struct perf_cgroup *cgrp = cpuctx->cgrp;
+       struct cgroup_subsys_state *css;
+
+       if (cgrp) {
+               for (css = &cgrp->css; css; css = css->parent) {
+                       cgrp = container_of(css, struct perf_cgroup, css);
+                       __update_cgrp_time(cgrp);
+               }
+       }
 }
 
 static inline void update_cgrp_time_from_event(struct perf_event *event)
@@ -449,6 +455,7 @@ perf_cgroup_set_timestamp(struct task_struct *task,
 {
        struct perf_cgroup *cgrp;
        struct perf_cgroup_info *info;
+       struct cgroup_subsys_state *css;
 
        /*
         * ctx->lock held by caller
@@ -459,8 +466,12 @@ perf_cgroup_set_timestamp(struct task_struct *task,
                return;
 
        cgrp = perf_cgroup_from_task(task, ctx);
-       info = this_cpu_ptr(cgrp->info);
-       info->timestamp = ctx->timestamp;
+
+       for (css = &cgrp->css; css; css = css->parent) {
+               cgrp = container_of(css, struct perf_cgroup, css);
+               info = this_cpu_ptr(cgrp->info);
+               info->timestamp = ctx->timestamp;
+       }
 }
 
 #define PERF_CGROUP_SWOUT      0x1 /* cgroup switch out every event */