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Subject: Re: [RFC PATCH] kmemleak: Scan all thread stacks
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Ingo Molnar <mingo@elte.hu>, "Paul E. McKenney" <paulmck@us.ibm.com>,
       linux-kernel@vger.kernel.org
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Date: Fri, 17 Jul 2009 19:01:09 +0200
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On Fri, 2009-07-17 at 17:57 +0100, Catalin Marinas wrote:
> On Fri, 2009-07-17 at 18:43 +0200, Ingo Molnar wrote:
> > * Catalin Marinas <catalin.marinas@arm.com> wrote:
> > > 2. Is it safe to use rcu_read_lock() and task_lock() when scanning the
> > >    corresponding kernel stack (thread_info structure)? The loop doesn't
> > >    do any modification to the task list. The reason for this is to
> > >    allow kernel preemption when scanning the stacks.
> > 
> > you cannot generally preempt while holding the RCU read-lock.
> 
> This may work with rcupreempt enabled. But, with classic RCU is it safe
> to call schedule (or cond_resched) while holding the RCU read-lock?

No.