Date: Thu, 12 Feb 2015 20:39:05 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Nicholas Mc Guire <der.herr@hofr.at>
Cc: Davidlohr Bueso <dave@stgolabs.net>, paulmck@linux.vnet.ibm.com,
        linux-kernel@vger.kernel.org, waiman.long@hp.com, peterz@infradead.org,
        raghavendra.kt@linux.vnet.ibm.com
Subject: Re: BUG: spinlock bad magic on CPU#0, migration/0/9
Message-ID: <20150212193905.GB28499@redhat.com>
References: <20150212003430.GA28656@linux.vnet.ibm.com> <1423710911.2046.50.camel@stgolabs.net> <20150212172805.GA20850@redhat.com> <20150212174144.GA21714@redhat.com> <20150212193210.GA7244@opentech.at>
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On 02/12, Nicholas Mc Guire wrote:
>
> On Thu, 12 Feb 2015, Oleg Nesterov wrote:
>
> > --- x/kernel/sched/completion.c
> > +++ x/kernel/sched/completion.c
> > @@ -274,7 +274,7 @@ bool try_wait_for_completion(struct comp
> >  	 * first without taking the lock so we can
> >  	 * return early in the blocking case.
> >  	 */
> > -	if (!ACCESS_ONCE(x->done))
> > +	if (!READ_ONCE(x->done))
> >  		return 0;
> >
> from looking at compiler.h I don't think that there would be a difference
> between ACCESS_ONCE() and READ_ONCE() in this case

Yes, this is unrelated "while at it" cosmetic change, now that we have
READ_ONCE() it makes more sense in this case.

Oleg.

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