linux-kernel - Re: [PATCH] rcutorture: Fix rcu_torture_pipe_update_one()/rcu_torture

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Date: Tue,  5 Mar 2024 14:24:20 +0800
From: linke li <lilinke99@...com>
To: joel@...lfernandes.org
Cc: boqun.feng@...il.com,
	dave@...olabs.net,
	frederic@...nel.org,
	jiangshanlai@...il.com,
	josh@...htriplett.org,
	lilinke99@...com,
	linux-kernel@...r.kernel.org,
	mathieu.desnoyers@...icios.com,
	paulmck@...nel.org,
	qiang.zhang1211@...il.com,
	quic_neeraju@...cinc.com,
	rcu@...r.kernel.org,
	rostedt@...dmis.org
Subject: Re: [PATCH] rcutorture: Fix rcu_torture_pipe_update_one()/rcu_torture_writer() data race and concurrency bug

> Anyway, a slightly related/different question:
> 
> Should that:
> WRITE_ONCE(rp->rtort_pipe_count, rp->rtort_pipe_count + 1);
> 
> Be:
> WRITE_ONCE(rp->rtort_pipe_count, READ_ONCE(rp->rtort_pipe_count) + 1);
> 
> ?

Hi, Joel. Sorry, I am not very sure about this. I do a little research on
it.

I looked through all code in kernel that looks like this, both kinds are
used. I also try to compile this file with and without the READ_ONCE in
WRITE_ONCE using gcc-9. Their binary is just the same. 

Thus I think in the current compiler version, they do not have a big
difference, but if the compiler wants to optimize more, maybe the latter
one is better.