linux-kernel - Re: [PATCH 1/4] s390: convert debug_info.ref_count from atomic_t to refcount

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Message-ID: <20170220133914.GQ6500@twins.programming.kicks-ass.net>
Date:   Mon, 20 Feb 2017 14:39:14 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Heiko Carstens <heiko.carstens@...ibm.com>
Cc:     Elena Reshetova <elena.reshetova@...el.com>,
        linux-kernel@...r.kernel.org, linux-edac@...r.kernel.org,
        x86@...nel.org, sparclinux@...r.kernel.org,
        linux-s390@...r.kernel.org, kvm@...r.kernel.org,
        gregkh@...uxfoundation.org, davem@...emloft.net,
        tglx@...utronix.de, mingo@...hat.com, tony.luck@...el.com,
        hpa@...or.com, Hans Liljestrand <ishkamiel@...il.com>,
        Kees Cook <keescook@...omium.org>,
        David Windsor <dwindsor@...il.com>
Subject: Re: [PATCH 1/4] s390: convert debug_info.ref_count from atomic_t to
 refcount_t

On Mon, Feb 20, 2017 at 02:24:24PM +0100, Heiko Carstens wrote:
> On Mon, Feb 20, 2017 at 01:06:18PM +0200, Elena Reshetova wrote:

> > @@ -361,7 +361,7 @@ debug_info_create(const char *name, int pages_per_area, int nr_areas,
> >          debug_area_last = rc;
> >          rc->next = NULL;
> >  
> > -	debug_info_get(rc);
> > +	refcount_set(&rc->ref_count, 1);
> 
> This is not wrong, but I will remove this hunk before applying your patch,
> since this doesn't look like an obvious correct change at first glance.

I suspect; but have not looked at the code; that this would otherwise
attempt to do a 0 -> 1 increment, which refcount_inc() will refuse (and
WARN) over.