perf/cgroup: Fix perf cgroup hierarchy support

BugLink: http://bugs.launchpad.net/bugs/1731971
commit be96b316deff35e119760982c43af74e606fa143 upstream.

The following commit:

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

made list_update_cgroup_event() skip setting cpuctx->cgrp if no cgroup event
targets %current's cgroup.

This breaks perf_event's hierarchical support because events which target one
of the ancestors get ignored.

Fix it by using cgroup_is_descendant() test instead of equality.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: David Carrillo-Cisneros <davidcc@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: kernel-team@fb.com
Fixes: 864c2357ca89 ("perf/core: Do not set cpuctx->cgrp for unscheduled cgroups")
Link: http://lkml.kernel.org/r/20171028164237.GA972780@devbig577.frc2.facebook.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 9ca98cb7d420372c085dfe6026193b4c53919ad3..5d4398d1fa19680bb5fba97711dd476b842564a3 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -906,9 +906,11 @@ list_update_cgroup_event(struct perf_event *event,
        cpuctx_entry = &cpuctx->cgrp_cpuctx_entry;
        /* cpuctx->cgrp is NULL unless a cgroup event is active in this CPU .*/
        if (add) {
+               struct perf_cgroup *cgrp = perf_cgroup_from_task(current, ctx);
+
                list_add(cpuctx_entry, this_cpu_ptr(&cgrp_cpuctx_list));
-               if (perf_cgroup_from_task(current, ctx) == event->cgrp)
-                       cpuctx->cgrp = event->cgrp;
+               if (cgroup_is_descendant(cgrp->css.cgroup, event->cgrp->css.cgroup))
+                       cpuctx->cgrp = cgrp;
        } else {
                list_del(cpuctx_entry);
                cpuctx->cgrp = NULL;