linux-kernel - Re: [PATCH 22/45] percpu_counter: Use get/put_online_cpus

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: <20130624180636.GB1918@mtj.dyndns.org>
Date:	Mon, 24 Jun 2013 11:06:36 -0700
From:	Tejun Heo <tj@...nel.org>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	tglx@...utronix.de, peterz@...radead.org, oleg@...hat.com,
	paulmck@...ux.vnet.ibm.com, rusty@...tcorp.com.au,
	mingo@...nel.org, akpm@...ux-foundation.org, namhyung@...nel.org,
	walken@...gle.com, vincent.guittot@...aro.org,
	laijs@...fujitsu.com, rostedt@...dmis.org,
	wangyun@...ux.vnet.ibm.com, xiaoguangrong@...ux.vnet.ibm.com,
	sbw@....edu, fweisbec@...il.com, zhong@...ux.vnet.ibm.com,
	nikunj@...ux.vnet.ibm.com, linux-pm@...r.kernel.org,
	linux-arch@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 22/45] percpu_counter: Use get/put_online_cpus_atomic()
 to prevent CPU offline

On Mon, Jun 24, 2013 at 10:55:35AM -0700, Tejun Heo wrote:
> > @@ -105,6 +106,7 @@ s64 __percpu_counter_sum(struct percpu_counter *fbc)
> >  		ret += *pcount;
> >  	}
> >  	raw_spin_unlock(&fbc->lock);
> > +	put_online_cpus_atomic();
> 
> I don't think this is necessary.  CPU on/offlining is explicitly
> handled via the hotplug callback which synchronizes through fbc->lock.
> __percpu_counter_sum() racing with actual on/offlining doesn't affect
> correctness and adding superflous get_online_cpus_atomic() around it
> can be misleading.

Ah, okay, so you added a debug feature which triggers warning if
online mask is accessed without synchronization.  Yeah, that makes
sense and while the above is not strictly necessary, it probably is
better to just add it rather than suppressing the warning in a
different way.  Can you please at least add a comment explaining that?

Thanks.

-- 
tejun
--
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/