From: Steven Rostedt <rostedt@goodmis.org>
To: John Stultz <john.stultz@linaro.org>
Cc: paulmck@kernel.org, Josh Triplett <josh@joshtriplett.org>,
lkml <linux-kernel@vger.kernel.org>,
Bjorn Andersson <bjorn.andersson@linaro.org>,
Saravana Kannan <saravanak@google.com>,
Todd Kjos <tkjos@google.com>, Stephen Boyd <sboyd@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: On trace_*_rcuidle functions in modules
Date: Wed, 15 Apr 2020 17:49:18 -0400 [thread overview]
Message-ID: <20200415174918.154a86d0@gandalf.local.home> (raw)
In-Reply-To: <CALAqxLW6jqr38bk8pp-Hom2=MLm3coTmzCP8MMfrDvMfx388=Q@mail.gmail.com>
On Wed, 15 Apr 2020 14:02:04 -0700
John Stultz <john.stultz@linaro.org> wrote:
>
> So in my case your concerns may not be a problem, but I guess
> generally it might. Though I'd hope the callback would be unregistered
> (and whatever waiting for the grace period to complete be done) before
> the module removal is complete. But maybe I'm still missing your
> point?
Hmm, you may have just brought up a problem here...
You're saying that cpu_pm_register_notifier() callers are called from non
RCU watching context? If that's the case, we have this:
int cpu_pm_unregister_notifier(struct notifier_block *nb)
{
return atomic_notifier_chain_unregister(&cpu_pm_notifier_chain, nb);
}
And this:
int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,
struct notifier_block *n)
{
unsigned long flags;
int ret;
spin_lock_irqsave(&nh->lock, flags);
ret = notifier_chain_unregister(&nh->head, n);
spin_unlock_irqrestore(&nh->lock, flags);
synchronize_rcu();
return ret;
}
Which means that if something registered a cpu_pm notifier, then
unregistered it, and freed whatever the notifier accesses, then there's a
chance that the synchronize_rcu() can return before the called notifier
finishes, and anything that notifier accesses could have been freed.
I believe that module code should not be able to be run in RCU non watching
context, and neither should notifiers. I think we just stumbled on a bug.
Paul?
-- Steve
next prev parent reply other threads:[~2020-04-15 21:49 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-15 2:20 On trace_*_rcuidle functions in modules John Stultz
2020-04-15 2:57 ` Paul E. McKenney
2020-04-15 3:47 ` John Stultz
2020-04-15 13:12 ` Paul E. McKenney
2020-04-15 12:53 ` Steven Rostedt
2020-04-15 19:56 ` John Stultz
2020-04-15 20:14 ` Steven Rostedt
2020-04-15 20:17 ` John Stultz
2020-04-15 20:41 ` Steven Rostedt
2020-04-15 21:02 ` John Stultz
2020-04-15 21:49 ` Steven Rostedt [this message]
2020-04-15 22:04 ` Paul E. McKenney
2020-04-15 22:42 ` Peter Zijlstra
2020-04-15 22:53 ` Steven Rostedt
2020-04-15 22:53 ` Paul E. McKenney
2020-04-15 22:51 ` Steven Rostedt
2020-04-15 22:54 ` Paul E. McKenney
2020-04-16 0:06 ` John Stultz
2020-04-16 0:48 ` Steven Rostedt
2020-04-16 1:02 ` Bjorn Andersson
2020-04-16 1:24 ` Steven Rostedt
2020-04-16 2:17 ` John Stultz
2020-04-15 22:07 ` John Stultz
2020-04-15 22:40 ` Peter Zijlstra
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