Date: Thu, 12 Nov 2015 11:32:03 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Stephane Eranian <eranian@google.com>
Cc: linux-kernel@vger.kernel.org, acme@redhat.com, mingo@elte.hu,
        ak@linux.intel.com, edumazet@google.com
Subject: Re: [PATCH v3 0/2] perf/core: rcu fixes
Message-ID: <20151112103203.GX17308@twins.programming.kicks-ass.net>
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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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