linux-kernel - Re: [PATCH v2] srcu: Improve comments about acceleration leak

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Date: Mon, 18 Dec 2023 13:13:30 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: Joel Fernandes <joel@...lfernandes.org>
Cc: linux-kernel@...r.kernel.org, Lai Jiangshan <jiangshanlai@...il.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Josh Triplett <josh@...htriplett.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Neeraj Upadhyay <neeraj.iitr10@...il.com>, rcu@...r.kernel.org
Subject: Re: [PATCH v2] srcu: Improve comments about acceleration leak

Le Sun, Dec 17, 2023 at 09:00:15PM -0500, Joel Fernandes a écrit :
> "Acceleration can never fail because the state of gp_seq value used
> for acceleration is <= the state of gp_seq used for advancing."
> 
> Does that sound correct now?

That can be confusing since acceleration relies on rcu_seq_snap() while
advance relies on rcu_seq_current(). And rcu_seq_snap() returns a snapshot
that may be above the subsequent rcu_seq_current() return value.

So it should rather be something like:

"The base current gp_seq value used to produce the snapshot has to
be <= the gp_seq used for advancing."

Thanks.