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[PATCH v3 0/2] perf/core: rcu fixes

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  [PATCH v3 0/2] perf/core: rcu fixes Stephane Eranian <eranian@google.com> - 2015-11-12 11:10 +0100
    Re: [PATCH v3 0/2] perf/core: rcu fixes Peter Zijlstra <peterz@infradead.org> - 2015-11-12 11:40 +0100

#1267779 — [PATCH v3 0/2] perf/core: rcu fixes

This short patch series fixes some issues with RCU locking in the generic
perf layer.

Patch 1 fixes cgroup switching rcu issues related to the fact that
perf_cgroup_sched_out() and perf_cgroup_sched_in() were missing some
rcu read lock to protect the reference to the cgroup. Consequently,
we moved the rcu readlock out of perf_cgroup_switch() to avoid double
calls.

Patch 2 reinforces the testing for the rcu locking in perf cgorup code.
Either we have to hold the rcu read lock or we must have the ctx->lock
which guarantees the task cannot leave the cgroup.

Thanks to Peter and Eric from their suggestions on how to fix this correctly.

Stephane Eranian (2):
  perf/core: fix RCU problem with cgroup context switching code
  perf/core: robustify perf_cgroup_from_task rcu checks

 arch/x86/kernel/cpu/perf_event_intel_cqm.c |  2 +-
 include/linux/perf_event.h                 |  6 ++++--
 kernel/events/core.c                       | 31 ++++++++++++++++++++----------
 3 files changed, 26 insertions(+), 13 deletions(-)

-- 
2.5.0

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#1267803

On Thu, Nov 12, 2015 at 11:00:02AM +0100, Stephane Eranian wrote:
> 
> This short patch series fixes some issues with RCU locking in the generic
> perf layer.
> 
> Patch 1 fixes cgroup switching rcu issues related to the fact that
> perf_cgroup_sched_out() and perf_cgroup_sched_in() were missing some
> rcu read lock to protect the reference to the cgroup. Consequently,
> we moved the rcu readlock out of perf_cgroup_switch() to avoid double
> calls.
> 
> Patch 2 reinforces the testing for the rcu locking in perf cgorup code.
> Either we have to hold the rcu read lock or we must have the ctx->lock
> which guarantees the task cannot leave the cgroup.
> 
> Thanks to Peter and Eric from their suggestions on how to fix this correctly.
> 
> Stephane Eranian (2):
>   perf/core: fix RCU problem with cgroup context switching code
>   perf/core: robustify perf_cgroup_from_task rcu checks

Thanks!
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