Re: [PATCH] cgroup, perf_event: Fix perf cgroup hierarchy support

[Peter Zijlstra]

On Sat, Oct 28, 2017 at 09:49:37AM -0700, Tejun Heo wrote:
> 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.

Right similar to:

  e6a5203399d1 ("perf/core: Fix cgroup time when scheduling descendants")


> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
> Fixes: 864c2357ca89 ("perf/core: Do not set cpuctx->cgrp for unscheduled cgroups")
> Cc: stable@xxxxxxxxxxxxxxx # v4.9+
> Cc: David Carrillo-Cisneros <davidcc@xxxxxxxxxx>

I think David left Google (I've had this email bounce), lets add
Stephane.

Cc: Stephane Eranian <eranian@xxxxxxxxx>


Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>

> ---
>  kernel/events/core.c |    7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 9d93db8..db2e630 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -901,9 +901,12 @@ 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;