Messages in this thread | | | From | Namhyung Kim <> | Date | Mon, 10 Jan 2022 11:49:22 -0800 | Subject | Re: [PATCH v3] perf/core: Fix cgroup event list management |
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Hi Marco,
On Mon, Jan 10, 2022 at 12:58 AM Marco Elver <elver@google.com> wrote: > > On Tue, 14 Dec 2021 at 00:22, Namhyung Kim <namhyung@kernel.org> wrote: > > > > The active cgroup events are managed in the per-cpu cgrp_cpuctx_list. > > This list is only accessed from current cpu and not protected by any > > locks. But from the commit ef54c1a476ae ("perf: Rework > > perf_event_exit_event()"), it's possible to access (actually modify) > > the list from another cpu. > > > > In the perf_remove_from_context(), it can remove an event from the > > context without an IPI when the context is not active. This is not > > safe with cgroup events which can have some active events in the > > context even if ctx->is_active is 0 at the moment. The target cpu > > might be in the middle of list iteration at the same time. > > > > If the event is enabled when it's about to be closed, it might call > > perf_cgroup_event_disable() and list_del() with the cgrp_cpuctx_list > > on a different cpu. > > > > This resulted in a crash due to an invalid list pointer access during > > the cgroup list traversal on the cpu which the event belongs to. > > > > Let's fallback to IPI to access the cgrp_cpuctx_list from that cpu. > > Similarly, perf_install_in_context() should use IPI for the cgroup > > events too. > > > > Cc: Marco Elver <elver@google.com> > > Signed-off-by: Namhyung Kim <namhyung@kernel.org> > > The final version needs: > > Fixes: ef54c1a476ae ("perf: Rework perf_event_exit_event()") > > so stable kernels will see it, unless this has already been picked up > in which case we need to email stable.
Right, it should go to the stable tree.
Peter, do you want me to resend a new version?
Thanks, Namhyung
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