linux-kernel - Re: [PATCH 3/7] sched: Use dl_bw

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Date:	Sat, 20 Sep 2014 21:32:12 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Kirill Tkhai <tkhai@...dex.ru>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Kirill Tkhai <ktkhai@...allels.com>
Subject: Re: [PATCH 3/7] sched: Use dl_bw_of() under RCU read lock

On Sat, Sep 20, 2014 at 11:25:39PM +0400, Kirill Tkhai wrote:
> On 20.09.2014 22:57, Peter Zijlstra wrote:
> > On Sat, Sep 20, 2014 at 08:51:28PM +0400, Kirill Tkhai wrote:
> >> From: Kirill Tkhai <ktkhai@...allels.com>
> >>
> >> dl_bw_of() dereferences rq->rd which has to have RCU read lock held.
> >> Probability of use-after-free and memory corruption aren't zero here.
> >>
> > 
> > Additionally we might want to add something like:
> > lockdep_assert_held_rcu() and put that in dl_bw_of() and other such
> > places.
> 
> Should we change (not now, in general) RCU-related pointers to use
> rcu_dereference() to have unlocked RCU warnings in dmesg? To catch
> a problems like that.
> 
> This may make code worse readable though.

Possibly, we should probably use rcu_assign_pointer() and
rcu_dereference() on rq->rd. Sometimes you can avoid that if you're
playing games with static objects, but I don't think that is true here.
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