linux-kernel - Re: [patch V2 11/16] x86/ioperm: Share I/O bitmap if identical

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Message-ID: <alpine.DEB.2.21.1911121051110.1833@nanos.tec.linutronix.de>
Date:   Tue, 12 Nov 2019 10:51:31 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Linus Torvalds <torvalds@...uxfoundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Willy Tarreau <w@....eu>, Juergen Gross <jgross@...e.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [patch V2 11/16] x86/ioperm: Share I/O bitmap if identical

On Tue, 12 Nov 2019, Peter Zijlstra wrote:
> On Mon, Nov 11, 2019 at 11:03:25PM +0100, Thomas Gleixner wrote:
> > @@ -59,8 +71,26 @@ long ksys_ioperm(unsigned long from, uns
> >  			return -ENOMEM;
> >  
> >  		memset(iobm->bits, 0xff, sizeof(iobm->bits));
> > +		refcount_set(&iobm->refcnt, 1);
> > +	}
> > +
> > +	/*
> > +	 * If the bitmap is not shared, then nothing can take a refcount as
> > +	 * current can obviously not fork at the same time. If it's shared
> > +	 * duplicate it and drop the refcount on the original one.
> > +	 */
> > +	if (refcount_read(&iobm->refcnt) > 1) {
> > +		iobm = kmemdup(iobm, sizeof(*iobm), GFP_KERNEL);
> > +		if (!iobm)
> > +			return -ENOMEM;
> > +		io_bitmap_exit();
> 		refcount_set(&iobm->refcnd, 1);

Indeed.