linux-kernel - Re: [PATCH tip/core/rcu 08/10] rcu: Add a TINY_PREEMPT

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1282061199.3268.1519.camel@gandalf.stny.rr.com>
Date:	Tue, 17 Aug 2010 12:06:39 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	josh@...htriplett.org, dvhltc@...ibm.com, niv@...ibm.com,
	tglx@...utronix.de, peterz@...radead.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH tip/core/rcu 08/10] rcu: Add a TINY_PREEMPT_RCU

On Tue, 2010-08-17 at 12:04 -0400, Steven Rostedt wrote:

> > Then we could go for the simpler:
> > 
> >   	--t->rcu_read_lock_nesting;
> >  	barrier();
> >         if (t->rcu_read_lock_nesting == 0 &&
> >              unlikely((t->rcu_read_unlock_special))
> 
> Yeah, that's what I meant, I was too lazy to remove the ACCESS_ONCE()
> from the cut and paste I did.
> 
> > 
> > Which puts a constraint across all memory accesses. I'd be fine with
> > that if you are afraid of too much micro-optimization (e.g. my
> > barrier2(a, b) proposal).
> 
> Not afraid, but just too much code for a simple solution.

IOW,

I think just pulling out the '--' and adding the barrier() is the proper
solution here. Compiler barriers are rather cheap.

Can we all agree on this solution?

-- Steve


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/