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

[Thomas Gleixner]

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.