linux-kernel - Re: [PATCH RFC tip/core/rcu 05/14] rcu: Abstract sequence counting from synchronize_sched

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: <20150709083809.GA14145@mwanda>
Date:	Thu, 9 Jul 2015 11:42:49 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, rostedt@...dmis.org,
	dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
	fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH RFC tip/core/rcu 05/14] rcu: Abstract sequence counting
 from synchronize_sched_expedited()

On Wed, Jul 01, 2015 at 03:18:04PM -0700, Paul E. McKenney wrote:
> > > +/* Adjust sequence number for start of update-side operation. */
> > > +static void rcu_seq_start(unsigned long *sp)
> > > +{
> > > +	WRITE_ONCE(*sp, *sp + 1);
> > > +	smp_mb(); /* Ensure update-side operation after counter increment. */
> > > +	WARN_ON_ONCE(!(*sp & 0x1));
> > > +}
> > 
> > That wants to be an ACQUIRE, right?
> 
> I cannot put the acquire in the WARN_ON_ONCE() because there
> are configurations where WARN_ON_ONCE() is compiled out.

I think WARN_ON_ONCE() always evaulates the condition.  You are maybe
thinking of VM_WARN_ON_ONCE().

I'm on a different thread where we almost introduced a bug by using
VM_WARN_ONCE() instead of WARN_ONCE().  The VM_WARNING conditions had
long execute times so they are weird.

regards,
dan carpenter

--
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/