linux-kernel - Re: [PATCH rcu] srcu: Guarantee non-negative return value from srcu_read

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Message-ID: <8b2552d8-0453-476a-8606-e8b761934783@paulmck-laptop>
Date: Tue, 22 Oct 2024 07:26:25 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Christoph Hellwig <hch@...radead.org>
Cc: Peter Zijlstra <peterz@...radead.org>, rcu@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel-team@...a.com,
	rostedt@...dmis.org, andrii@...nel.org
Subject: Re: [PATCH rcu] srcu: Guarantee non-negative return value from
 srcu_read_lock()

On Tue, Oct 22, 2024 at 12:13:12AM -0700, Christoph Hellwig wrote:
> On Tue, Oct 22, 2024 at 09:10:18AM +0200, Peter Zijlstra wrote:
> > Ah, well, the thing that got us here is that we (Andrii and me) wanted
> > to use -1 as an 'invalid' value to indicate SRCU is not currently in
> > use.
> > 
> > So it all being int is really rather convenient :-)
> 
> Then please document that use.  Maybe even with a symolic name for
> -1 that clearly describes these uses.

Would this work?

#define SRCU_INVALID_INDEX -1

Whatever the name, maybe Peter and Andrii define this under #ifndef
right now, and we get it into include/linux/srcu.h over time.

Or is there a better way?  Or name, for that matter.

							Thanx, Paul