linux-kernel - Re: [PATCH] arm: smp: Avoid false positive CPU hotplug Lockdep-RCU splat

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Message-ID: <c567c622-1ee1-4828-8730-62bf6bfc2ecc@nokia.com>
Date: Fri, 8 Mar 2024 11:20:58 +0100
From: Stefan Wiehler <stefan.wiehler@...ia.com>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Russell King <linux@...linux.org.uk>,
 "Paul E. McKenney" <paulmck@...nel.org>,
 Joel Fernandes <joel@...lfernandes.org>,
 Josh Triplett <josh@...htriplett.org>, Steven Rostedt <rostedt@...dmis.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Lai Jiangshan <jiangshanlai@...il.com>, Zqiang <qiang.zhang1211@...il.com>,
 linux-arm-kernel@...ts.infradead.org, rcu@...r.kernel.org,
 linux-kernel@...r.kernel.org, Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [PATCH] arm: smp: Avoid false positive CPU hotplug Lockdep-RCU
 splat

> I'm not sure this is a false-positive: if you traverse an RCU-list
> without RCU watching the CPU, then a grace period may pass, the next
> list can be garbage and you can go anywhere from the list. Or am I
> missing something that a CPU hotplug can block a grace period?
Thanks for the feedback! Yes, calling it a false positive is probably not
correct, I will remove that. However, as Russell has explained in a previous
email, the spinlock is fundamental for ASID handling and cannot be removed.

@Russell, I will submit to the patch tracking system then.