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

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Message-ID: <20111123173313.GB29639@google.com>
Date:	Wed, 23 Nov 2011 09:33:13 -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

Hello, Steven.

On Wed, Nov 23, 2011 at 12:06:40PM -0500, Steven Rostedt wrote:
> > So, synchronized_sched() being called after isn't relevant.  We want
> > smp_wmb() between data structure initialization and assignment of the
> > new pointer.
> 
> Ah, you're saying that we need to guarantee that the allocated filter is
> seen before we update the call->filter to point to it. OK, fair enough,
> this does look like a bug fix.
> 
> Is it big enough to be considered for stable?

It's unlikely to happen for x86 or arm and that probably is the
biggest reason there hasn't already been a bug report.  It isn't very
urgent but at the same time the change is almost trivial, so marking
it for stable is a pretty safe bet.  I lean toward marking it for
stable but the leaning isn't too strong. :)

Thanks.

-- 
tejun
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