From: Peter Zijlstra <peterz@infradead.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Muchun Song <songmuchun@bytedance.com>,
mingo@kernel.org, juri.lelli@redhat.com,
vincent.guittot@linaro.org, linux-kernel@vger.kernel.org,
dietmar.eggemann@arm.com, rostedt@goodmis.org,
bsegall@google.com, mgorman@suse.de, joel@joelfernandes.org
Subject: Re: [PATCH] sched/fair: Fix call walk_tg_tree_from() without hold rcu_lock
Date: Tue, 21 Apr 2020 18:24:52 +0200 [thread overview]
Message-ID: <20200421162452.GV20730@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200421154312.GO17661@paulmck-ThinkPad-P72>
On Tue, Apr 21, 2020 at 08:43:12AM -0700, Paul E. McKenney wrote:
> On Tue, Apr 21, 2020 at 03:52:58PM +0200, Peter Zijlstra wrote:
> > On Mon, Apr 06, 2020 at 08:10:08PM +0800, Muchun Song wrote:
> > > The walk_tg_tree_from() caller must hold rcu_lock,
> >
> > Not quite; with the RCU unification done 'recently' having preemption
> > disabled is sufficient. AFAICT preemption is disabled.
> >
> > In fact; and I mentioned this to someone the other day, perhaps Joel; we
> > can go and delete a whole bunch of rcu_read_lock() from the scheduler --
> > basically undo all the work we did after RCU was split many years ago.
>
> "If only I knew then what I know now..."
>
> Then again, I suspect that we all have ample opportunity to use that
> particular old phrase. ;-)
Quite so; I'm just fearing that rcu-lockdep annotation stuff. IIRC that
doesn't (nor can it, in general) consider the implicit preempt-disable
from locks and such for !PREEMPT builds.
next prev parent reply other threads:[~2020-04-21 16:25 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-06 12:10 [PATCH] sched/fair: Fix call walk_tg_tree_from() without hold rcu_lock Muchun Song
2020-04-06 18:17 ` bsegall
2020-04-13 15:00 ` [External] " 宋牧春
2020-04-21 13:52 ` Peter Zijlstra
2020-04-21 15:43 ` Paul E. McKenney
2020-04-21 16:24 ` Peter Zijlstra [this message]
2020-04-21 17:39 ` Paul E. McKenney
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