linux-kernel - Re: [PATCH v13 03/17] preempt: Introduce HARDIRQ_DISABLE

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Message-ID: <87pla386cp.fsf@t14s.mail-host-address-is-not-set>
Date: Fri, 31 Oct 2025 15:59:34 +0100
From: Andreas Hindborg <a.hindborg@...nel.org>
To: Lyude Paul <lyude@...hat.com>, rust-for-linux@...r.kernel.org, Thomas
 Gleixner <tglx@...utronix.de>, Boqun Feng <boqun.feng@...il.com>,
 linux-kernel@...r.kernel.org, Daniel Almeida
 <daniel.almeida@...labora.com>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot
 <vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel
 Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>
Subject: Re: [PATCH v13 03/17] preempt: Introduce HARDIRQ_DISABLE_BITS

Lyude Paul <lyude@...hat.com> writes:

> From: Boqun Feng <boqun.feng@...il.com>
>
> In order to support preempt_disable()-like interrupt disabling, that is,
> using part of preempt_count() to track interrupt disabling nested level,
> change the preempt_count() layout to contain 8-bit HARDIRQ_DISABLE
> count.
>
> Note that HARDIRQ_BITS and NMI_BITS are reduced by 1 because of this,
> and it changes the maximum of their (hardirq and nmi) nesting level.
>
> Signed-off-by: Boqun Feng <boqun.feng@...il.com>
> Signed-off-by: Lyude Paul <lyude@...hat.com>
> ---
>  include/linux/preempt.h | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/preempt.h b/include/linux/preempt.h
> index 9580b972e1545..bbd2e51363d8f 100644
> --- a/include/linux/preempt.h
> +++ b/include/linux/preempt.h
> @@ -17,6 +17,8 @@
>   *
>   * - bits 0-7 are the preemption count (max preemption depth: 256)
>   * - bits 8-15 are the softirq count (max # of softirqs: 256)
> + * - bits 16-23 are the hardirq disable count (max # of hardirq disable: 256)
> + * - bits 24-27 are the hardirq count (max # of hardirqs: 16)
>   * - bit 28 is the NMI flag (no nesting count, tracked separately)
>   *
>   * The hardirq count could in theory be the same as the number of
> @@ -30,29 +32,34 @@
>   *
>   *         PREEMPT_MASK:	0x000000ff
>   *         SOFTIRQ_MASK:	0x0000ff00
> - *         HARDIRQ_MASK:	0x000f0000
> + * HARDIRQ_DISABLE_MASK:	0x00ff0000
> + *         HARDIRQ_MASK:	0x0f000000
>   *             NMI_MASK:	0x10000000
>   * PREEMPT_NEED_RESCHED:	0x80000000
>   */
>  #define PREEMPT_BITS	8
>  #define SOFTIRQ_BITS	8
> +#define HARDIRQ_DISABLE_BITS	8
>  #define HARDIRQ_BITS	4
>  #define NMI_BITS	1
>  
>  #define PREEMPT_SHIFT	0
>  #define SOFTIRQ_SHIFT	(PREEMPT_SHIFT + PREEMPT_BITS)
> -#define HARDIRQ_SHIFT	(SOFTIRQ_SHIFT + SOFTIRQ_BITS)
> +#define HARDIRQ_DISABLE_SHIFT	(SOFTIRQ_SHIFT + SOFTIRQ_BITS)
> +#define HARDIRQ_SHIFT	(HARDIRQ_DISABLE_SHIFT + HARDIRQ_DISABLE_BITS)
>  #define NMI_SHIFT	(HARDIRQ_SHIFT + HARDIRQ_BITS)
>  
>  #define __IRQ_MASK(x)	((1UL << (x))-1)
>  
>  #define PREEMPT_MASK	(__IRQ_MASK(PREEMPT_BITS) << PREEMPT_SHIFT)
>  #define SOFTIRQ_MASK	(__IRQ_MASK(SOFTIRQ_BITS) << SOFTIRQ_SHIFT)
> +#define HARDIRQ_DISABLE_MASK	(__IRQ_MASK(SOFTIRQ_BITS) << HARDIRQ_DISABLE_SHIFT)

Should this be HARDIRQ_DISABLE_BITS rather than SOFTIRQ_BITS ?


Best regards,
Andreas Hindborg