linux-kernel - [RFC RESEND v10 01/14] preempt: Introduce HARDIRQ_DISABLE

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Message-ID: <20250527222254.565881-2-lyude@redhat.com>
Date: Tue, 27 May 2025 18:21:42 -0400
From: Lyude Paul <lyude@...hat.com>
To: 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: [RFC RESEND v10 01/14] preempt: Introduce HARDIRQ_DISABLE_BITS

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 | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index b0af8d4ef6e66..809af7b57470a 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -17,6 +17,7 @@
  *
  * - 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)
  *
  * The hardirq count could in theory be the same as the number of
  * interrupts in the system, but we run all interrupt handlers with
@@ -26,29 +27,34 @@
  *
  *         PREEMPT_MASK:	0x000000ff
  *         SOFTIRQ_MASK:	0x0000ff00
- *         HARDIRQ_MASK:	0x000f0000
- *             NMI_MASK:	0x00f00000
+ * HARDIRQ_DISABLE_MASK:	0x00ff0000
+ *         HARDIRQ_MASK:	0x07000000
+ *             NMI_MASK:	0x38000000
  * PREEMPT_NEED_RESCHED:	0x80000000
  */
 #define PREEMPT_BITS	8
 #define SOFTIRQ_BITS	8
-#define HARDIRQ_BITS	4
-#define NMI_BITS	4
+#define HARDIRQ_DISABLE_BITS	8
+#define HARDIRQ_BITS	3
+#define NMI_BITS	3
 
 #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)
 
-- 
2.49.0