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Message-ID: <1332409996.18960.511.camel@twins>
Date: Thu, 22 Mar 2012 10:53:16 +0100
From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
To: Ari Savolainen <ari.m.savolainen@...il.com>
Cc: Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf: Fix RCU dereference check in perf_event_comm
On Thu, 2012-03-22 at 01:43 +0200, Ari Savolainen wrote:
> The warning below is printed when executing a command like
> sudo perf record su - user -c "echo hello"
>
> It's fixed by moving the call of perf_event_comm to be protected
> by the task lock.
That seems like a rather poor solution since it increases the lock hold
time for no explained reason.
> include/linux/cgroup.h:567 suspicious rcu_dereference_check() usage!
> [<ffffffff8109be55>] lockdep_rcu_suspicious+0xe5/0x100
> [<ffffffff811131fa>] perf_event_comm+0x37a/0x4d0
So where exactly is this, perf_event_comm_event() takes rcu_read_lock()
so I presume its before that.
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