[PATCH v13 03/17] preempt: Introduce HARDIRQ_DISABLE_BITS

Lyude Paul
2025-10-13T15:54:00Z

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