1. Patchew
  2. linux
  3. [PATCH v13 00/17] Refcounted interrupts, SpinLockIrq for rust
  4. View patch

[PATCH v13 03/17] preempt: Introduce HARDIRQ_DISABLE_BITS

Lyude Paul posted 17 patches 2 months ago
There is a newer version of this series
[PATCH v13 03/17] preempt: Introduce HARDIRQ_DISABLE_BITS
Posted by Lyude Paul 2 months ago 
From: Boqun Feng <boqun.feng@gmail.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@gmail.com>
Signed-off-by: Lyude Paul <lyude@redhat.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)
 #define HARDIRQ_MASK	(__IRQ_MASK(HARDIRQ_BITS) << HARDIRQ_SHIFT)
 #define NMI_MASK	(__IRQ_MASK(NMI_BITS)     << NMI_SHIFT)
 
 #define PREEMPT_OFFSET	(1UL << PREEMPT_SHIFT)
 #define SOFTIRQ_OFFSET	(1UL << SOFTIRQ_SHIFT)
+#define HARDIRQ_DISABLE_OFFSET	(1UL << HARDIRQ_DISABLE_SHIFT)
 #define HARDIRQ_OFFSET	(1UL << HARDIRQ_SHIFT)
 #define NMI_OFFSET	(1UL << NMI_SHIFT)
 
-- 
2.51.0
Re: [PATCH v13 03/17] preempt: Introduce HARDIRQ_DISABLE_BITS
Posted by Andreas Hindborg 1 month, 2 weeks ago 
Lyude Paul <lyude@redhat.com> writes:

> From: Boqun Feng <boqun.feng@gmail.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@gmail.com>
> Signed-off-by: Lyude Paul <lyude@redhat.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
Re: [PATCH v13 03/17] preempt: Introduce HARDIRQ_DISABLE_BITS
Posted by Boqun Feng 1 month, 2 weeks ago 
On Fri, Oct 31, 2025 at 03:59:34PM +0100, Andreas Hindborg wrote:
> Lyude Paul <lyude@redhat.com> writes:
> 
> > From: Boqun Feng <boqun.feng@gmail.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@gmail.com>
> > Signed-off-by: Lyude Paul <lyude@redhat.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 ?
> 

Good catch! Yes, it' should be HARDIRQ_DISABLE_BITS. Thank you!

Regards,
Boqun

> 
> Best regards,
> Andreas Hindborg
> 
>

Patchew 2.1-devel-b67e4c2

© 2016 - 2025 Red Hat, Inc.