linux-kernel - Re: [RFC PATCH] kmemleak: Scan all thread stacks

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Message-ID: <20090722161809.GH6757@linux.vnet.ibm.com>
Date:	Wed, 22 Jul 2009 09:18:09 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] kmemleak: Scan all thread stacks

On Fri, Jul 17, 2009 at 07:01:09PM +0200, Peter Zijlstra wrote:
> 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@....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.

What Peter said!  ;-)

However, you might be able to use SRCU (http://lwn.net/Articles/202847/),
which does allow blocking within read-side critical sections.

							Thanx, Paul
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