Messages in this thread | | | Date | Mon, 13 Dec 2021 22:08:59 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2] perf/core: Fix cgroup event list management |
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On Sun, Dec 12, 2021 at 10:59:36PM -0800, Namhyung Kim wrote: > The active cgroup events are managed in the per-cpu cgrp_cpuctx_list. > This list is accessed from current cpu and not protected by any locks. > But from the commit ef54c1a476ae ("perf: Rework > perf_event_exit_event()"), this assumption does not hold true anymore. > > In the perf_remove_from_context(), it can remove an event from the > context without an IPI when the context is not active. I think it > assumes task event context, but it's possible for cpu event context
Yes, event_function_call() in general doesn't work, but for cpu events it does.
> only with cgroup events can be inactive at the moment - and it might > become active soon.
It can't, we're holding ctx->mutex and ctx->lock, and since it's a cpu event, that's cpuctx.
But yes, cgrp_cpuctx_list relies on being strictly per-cpu and I can't come up with a better solution either, doing those IPIs suck but...
But please, put in a comment like:
/* * Cgroup events are per-CPU events, and must IPI because of * cgrp_cpuctx_list. */ if (!ctx->is_active || !is_cgroup_event(event)) {
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