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SubjectRe: [PATCH v2] perf/core: Fix installing cgroup event into cpu
On Wed, Jan 24, 2018 at 03:50:10PM +0800, linxiulei@gmail.com wrote:
> From: "leilei.lin" <leilei.lin@alibaba-inc.com>
>
> Do not install cgroup event into the CPU context if the cgroup
> is not running on this CPU
>
> While there is no task of cgroup running specified CPU, current
> kernel still install cgroup event into CPU context, that causes
> another cgroup event can't be installed into this CPU.

This changelog doesn't really cover the extend of the changes done.


> Signed-off-by: leilei.lin <leilei.lin@alibaba-inc.com>
> ---
> kernel/events/core.c | 44 +++++++++++++++++++++++++++++++-------------
> 1 file changed, 31 insertions(+), 13 deletions(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 4df5b69..f766b60 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -933,31 +933,36 @@ list_update_cgroup_event(struct perf_event *event,
> {
> struct perf_cpu_context *cpuctx;
> struct list_head *cpuctx_entry;
> + struct perf_cgroup *cgrp;
>
> if (!is_cgroup_event(event))
> return;
>
> /*
> * Because cgroup events are always per-cpu events,
> * this will always be called from the right CPU.
> */
> cpuctx = __get_cpu_context(ctx);
> + cgrp = perf_cgroup_from_task(current, ctx);
>
> + /* cpuctx->cgrp is NULL unless a cgroup event is running in this CPU .*/
> + if (cgroup_is_descendant(cgrp->css.cgroup, event->cgrp->css.cgroup)) {
> + if (add)
> cpuctx->cgrp = cgrp;
> + else
> + cpuctx->cgrp = NULL;
> }
> +
> + if (add && ctx->nr_cgroups++)
> + return;
> + else if (!add && --ctx->nr_cgroups)
> + return;
> +
> + cpuctx_entry = &cpuctx->cgrp_cpuctx_entry;
> + if (add)
> + list_add(cpuctx_entry, this_cpu_ptr(&cgrp_cpuctx_list));
> + else
> + list_del(cpuctx_entry);
> }

I'm a little confused; you unconditionally set cpuctx->cgrp for every
add/delete.

So if we have >1 cgroup events on, and we remove one, you still clear
cpuctx->cgrp, that seems wrong.

Why did you change that? The Changelog doesn't include enough clues for
me to know what you were trying to do.

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