linux-kernel - Re: [RFC] WRITE_ONCE

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Message-ID: <20200419182957.GA36919@carbon>
Date:   Sun, 19 Apr 2020 21:29:57 +0300
From:   Petko Manolov <petko.manolov@...sulko.com>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     "Paul E . McKenney" <paulmck@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] WRITE_ONCE_INC() and friends

On 20-04-19 18:02:50, David Laight wrote:
> From: Petko Manolov
> > Sent: 19 April 2020 10:45
> > Recently I started reading up on KCSAN and at some point I ran into stuff like:
> > 
> > WRITE_ONCE(ssp->srcu_lock_nesting[idx], ssp->srcu_lock_nesting[idx] + 1);
> > WRITE_ONCE(p->mm->numa_scan_seq, READ_ONCE(p->mm->numa_scan_seq) + 1);
> 
> If all the accesses use READ/WRITE_ONCE() why not just mark the structure 
> field 'volatile'?

This is a bit heavy.  I guess you've read this one: 

	https://lwn.net/Articles/233479/

And no, i am not sure all accesses are through READ/WRITE_ONCE().  If, for 
example, all others are from withing spin_lock/unlock pairs then we _may_ not 
need READ/WRITE_ONCE().

I merely proposed the _INC() variant for better readability.


		Petko