From: Joel Fernandes <joel@joelfernandes.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: linux-kernel@vger.kernel.org,
Neeraj Upadhyay <neeraju@codeaurora.org>,
Josh Triplett <josh@joshtriplett.org>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
rcu@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH 1/2] rcu/tree: Add a warning if CPU being onlined did not report QS already
Date: Fri, 7 Aug 2020 11:37:32 -0400 [thread overview]
Message-ID: <20200807153732.GA2865655@google.com> (raw)
In-Reply-To: <20200731034825.GI9247@paulmck-ThinkPad-P72>
Hi Paul,
On Thu, Jul 30, 2020 at 08:48:25PM -0700, Paul E. McKenney wrote:
[...]
> > And I could make the comment here as:
> > /*
> > * Delete QS reporting from here, by June 2021, if the warning does not
> > * fire. Leave the warning indefinitely. Check RCU design requirements
> > * in Documentation/RCU/ about CPU hotplug requirements.
> > */
>
> Rather than decide for our future selves, could we please just suggest
> reviewing this on June 2021? Or, given enterprise distro schedules,
> 2024. :-/
I am replacing it with the following, let me know if any objections, thanks:
+ * XXX: The following rcu_report_qs_rnp() is redundant. If the below
+ * warning does not fire, consider replacing it with the "else" block,
+ * by June 2021 or so. The rationale for this is as follows: The CPU
+ * onlining path does not need to report QS for an offline CPU. Either
+ * the QS should have reported during CPU offlining, or during
+ * rcu_gp_init() if it detected a race with either CPU offlining or
+ * task unblocking on previously offlined CPUs. To avoid deadlocks
+ * related to waiting on timers or cpu hotplug locks, only those paths
+ * do the QS reporting for offline CPUs.
thanks,
- Joel
>
> Thanx, Paul
>
> > I will post my v3 with changes to the requirements document.
> >
> > Let me know any other comments, thanks,
> >
> > - Joel
> >
next prev parent reply other threads:[~2020-08-07 15:37 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-30 3:02 [PATCH 1/2] rcu/tree: Add a warning if CPU being onlined did not report QS already Joel Fernandes (Google)
2020-07-30 3:02 ` [PATCH 2/2] rcu/tree: Clarify comments about FQS loop reporting quiescent states Joel Fernandes (Google)
2020-07-30 3:25 ` Joel Fernandes
2020-07-30 16:35 ` Paul E. McKenney
2020-07-31 1:21 ` Joel Fernandes
2020-07-31 1:34 ` Paul E. McKenney
2020-07-30 16:21 ` [PATCH 1/2] rcu/tree: Add a warning if CPU being onlined did not report QS already Paul E. McKenney
2020-07-31 1:08 ` Joel Fernandes
2020-07-31 1:42 ` Joel Fernandes
2020-07-31 3:48 ` Paul E. McKenney
2020-08-07 15:37 ` Joel Fernandes [this message]
2020-08-07 15:45 ` Joel Fernandes
-- strict thread matches above, loose matches on Subject: below --
2020-09-29 19:29 Joel Fernandes (Google)
2020-10-02 4:39 ` Paul E. McKenney
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