Re: [PATCH v2 12/12] s390/preempt: Enable HAS_SEPARATE_PREEMPT_RESCHED_BITS

[Peter Zijlstra <peterz@infradead.org>]

On Tue, May 26, 2026 at 08:21:48AM -0700, Boqun Feng wrote:
> From: Heiko Carstens <hca@linux.ibm.com>
> 
> Convert s390's preempt_count to 64 bit, and change the preempt
> primitives accordingly.
> 
> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
> Signed-off-by: Boqun Feng <boqun@kernel.org>
> Link: https://patch.msgid.link/20260509181249.16281C67-hca@linux.ibm.com
> ---
>  arch/s390/Kconfig               |  1 +
>  arch/s390/include/asm/lowcore.h | 13 +++++++----
>  arch/s390/include/asm/preempt.h | 41 +++++++++++++++------------------
>  3 files changed, 29 insertions(+), 26 deletions(-)
> 
> diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
> index ecbcbb781e40..cbbca82f8443 100644
> --- a/arch/s390/Kconfig
> +++ b/arch/s390/Kconfig
> @@ -276,6 +276,7 @@ config S390
>  	select PCI_MSI			if PCI
>  	select PCI_MSI_ARCH_FALLBACKS	if PCI_MSI
>  	select PCI_QUIRKS		if PCI
> +	select HAS_SEPARATE_PREEMPT_RESCHED_BITS
>  	select SPARSE_IRQ
>  	select SWIOTLB
>  	select SYSCTL_EXCEPTION_TRACE
> diff --git a/arch/s390/include/asm/lowcore.h b/arch/s390/include/asm/lowcore.h
> index 50ffe75adeb4..0974ab278169 100644
> --- a/arch/s390/include/asm/lowcore.h
> +++ b/arch/s390/include/asm/lowcore.h
> @@ -160,10 +160,15 @@ struct lowcore {
>  	/* SMP info area */
>  	__u32	cpu_nr;				/* 0x03a0 */
>  	__u32	softirq_pending;		/* 0x03a4 */
> -	__s32	preempt_count;			/* 0x03a8 */
> -	__u32	spinlock_lockval;		/* 0x03ac */
> -	__u32	spinlock_index;			/* 0x03b0 */
> -	__u8	pad_0x03b4[0x03b8-0x03b4];	/* 0x03b4 */
> +	union {
> +		struct {
> +			__u32	need_resched;	/* 0x03a8 */
> +			__u32	count;		/* 0x03ac */
> +		} preempt;
> +		__u64	preempt_count;		/* 0x03a8 */
> +	};

I'm a little confused by this union; afaict it isn't actually used.