linux-kernel - Re: [PATCH 1/2] trace_events_filter: use rcu_assign_pointer() when setting ftrace_event

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Message-ID: <20111123161203.GC25780@google.com>
Date:	Wed, 23 Nov 2011 08:12:03 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...hat.com>,
	linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH 1/2] trace_events_filter: use rcu_assign_pointer() when
 setting ftrace_event_call->filter

On Wed, Nov 23, 2011 at 08:06:53AM -0800, Tejun Heo wrote:
> otherwise, it may fetch the old values from before the new area is
> initialized on archs where data dependency barrier isn't noop.

I think this can be a problem on archs where dd barrier is noop but
wmb is not.  dd barrier is implied on every read access but nothing
guarantees the updating CPU sends out write for the pointer assignment
before initialization of the new area.

Thanks.

-- 
tejun
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