From: Frederic Weisbecker <frederic@kernel.org>
To: Joel Fernandes <joelagnelf@nvidia.com>
Cc: linux-kernel@vger.kernel.org,
"Paul E. McKenney" <paulmck@kernel.org>,
Neeraj Upadhyay <neeraj.upadhyay@kernel.org>,
Josh Triplett <josh@joshtriplett.org>,
Boqun Feng <boqun.feng@gmail.com>,
Uladzislau Rezki <urezki@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Zqiang <qiang.zhang@linux.dev>, Jonathan Corbet <corbet@lwn.net>,
rcu@vger.kernel.org, linux-doc@vger.kernel.org
Subject: Re: [PATCH] rcu: Document concurrent quiescent state reporting for offline CPUs
Date: Mon, 7 Jul 2025 16:22:08 +0200 [thread overview]
Message-ID: <aGvYEFikpNdX-lGE@localhost.localdomain> (raw)
In-Reply-To: <20250707033208.361677-1-joelagnelf@nvidia.com>
Le Sun, Jul 06, 2025 at 11:32:08PM -0400, Joel Fernandes a écrit :
> The synchronization of CPU offlining with GP initialization is confusing
> to put it mildly (rightfully so as the issue it deals with is complex).
> Recent discussions brought up a question -- what prevents the
> rcu_implicit_dyntick_qs() from warning about QS reports for offline
> CPUs (missing QS reports for offline CPUs causing indefinite hangs).
>
> QS reporting for now-offline CPUs should only happen from:
> - gp_init()
> - rcutree_cpu_report_dead()
>
> Add some documentation on this and refer to it from comments in the code
> explaining how QS reporting is not missed when these functions are
> concurrently running.
>
> I referred heavily to this post [1] about the need for the ofl_lock.
> [1] https://lore.kernel.org/all/20180924164443.GF4222@linux.ibm.com/
>
> [ Applied paulmck feedback on moving documentation to Requirements.rst ]
>
> Link: https://lore.kernel.org/all/01b4d228-9416-43f8-a62e-124b92e8741a@paulmck-laptop/
> Co-developed-by: Paul E. McKenney <paulmck@kernel.org>
> Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Very nice and welcome!!!
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
--
Frederic Weisbecker
SUSE Labs
next prev parent reply other threads:[~2025-07-07 14:22 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-07-07 3:32 [PATCH] rcu: Document concurrent quiescent state reporting for offline CPUs Joel Fernandes
2025-07-07 14:22 ` Frederic Weisbecker [this message]
2025-07-07 14:27 ` Joel Fernandes
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