Re: [PATCH 12/24] s390/preempt: Enable HAS_SEPARATE_PREEMPT_RESCHED_BITS

[Heiko Carstens]

On Mon, Aug 03, 2026 at 01:40:32PM +0200, Peter Zijlstra wrote:
> On Fri, Jul 31, 2026 at 01:30:13PM -0700, Boqun Feng wrote:
> 
> > @@ -26,25 +23,25 @@
> >   */
> >  static __always_inline int preempt_count(void)
> >  {
> > -	unsigned long lc_preempt, count;
> > +	unsigned long lc_preempt;
> > +	int count;
> >  
> > -	BUILD_BUG_ON(sizeof_field(struct lowcore, preempt_count) != sizeof(int));
> > -	lc_preempt = offsetof(struct lowcore, preempt_count);
> > +	lc_preempt = offsetof(struct lowcore, preempt.count);
> >  	/* READ_ONCE(get_lowcore()->preempt_count) & ~PREEMPT_NEED_RESCHED */
> 
> If I'm not mistaken, this comment is no longer accurate, since
> NEED_RESCHED lives in the high word and you're only loading the low
> word.

True. Something like

  	/* READ_ONCE(get_lowcore()->preempt.count) (without PREEMPT_NEED_RESCHED) */

might be better.

> >  	asm_inline(
> > -		ALTERNATIVE("llgt	%[count],%[offzero](%%r0)\n",
> > -			    "llgt	%[count],%[offalt](%%r0)\n",
> > +		ALTERNATIVE("ly		%[count],%[offzero](%%r0)\n",
> > +			    "ly		%[count],%[offalt](%%r0)\n",
> >  			    ALT_FEATURE(MFEATURE_LOWCORE))
> >  		: [count] "=d" (count)
> >  		: [offzero] "i" (lc_preempt),
> >  		  [offalt] "i" (lc_preempt + LOWCORE_ALT_ADDRESS),
> > -		  "m" (((struct lowcore *)0)->preempt_count));
> > +		  "m" (((struct lowcore *)0)->preempt.count));
> >  	return count;
> >  }