From: Boqun Feng <boqun@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Ingo Molnar" <mingo@kernel.org>, "Will Deacon" <will@kernel.org>,
"Boqun Feng" <boqun@kernel.org>,
"Waiman Long" <longman@redhat.com>, "Gary Guo" <gary@garyguo.net>,
"Alice Ryhl" <aliceryhl@google.com>,
"Lyude Paul" <lyude@redhat.com>,
"Daniel Almeida" <daniel.almeida@collabora.com>,
"Onur Özkan" <work@onurozkan.dev>,
"Miguel Ojeda" <ojeda@kernel.org>,
"Danilo Krummrich" <dakr@kernel.org>,
linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org,
"Shrikanth Hegde" <sshegde@linux.ibm.com>
Subject: [PATCH 3/4] irq: Explain better on NMI_MASK overflow condition
Date: Mon, 10 Aug 2026 21:17:13 -0700 [thread overview]
Message-ID: <20260811041714.27679-4-boqun@kernel.org> (raw)
In-Reply-To: <20260811041714.27679-1-boqun@kernel.org>
Currently __preempt_count_nmi_enter() uses 15 as the maximum NMI nesting
level, and it's because 4 bits are used to represent the nesting level
of NMI. Replace the tautological comment with a more direct mention to
the 4 bits limitation to help readers understand this condition.
Suggested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Boqun Feng <boqun@kernel.org>
---
include/linux/hardirq.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index 73b48dd9f135..2648c49cd8f6 100644
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -108,7 +108,7 @@ DECLARE_PER_CPU(unsigned int, nmi_nesting);
#define __preempt_count_nmi_enter() \
do { \
__preempt_count_add(HARDIRQ_OFFSET); \
- /* Maximum NMI nesting is 15. */ \
+ /* NMI nesting is represented in 4 bits. */ \
BUG_ON(__this_cpu_read(nmi_nesting) >= 15); \
__this_cpu_inc(nmi_nesting); \
preempt_count_set(preempt_count() | NMI_MASK); \
--
2.50.1 (Apple Git-155)
next prev parent reply other threads:[~2026-08-11 4:17 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-07 7:01 [PATCH v5 00/18] Refcounted interrupt disable and SpinLockIrq for Rust Boqun Feng
2026-08-07 7:01 ` [PATCH v5 01/18] preempt: Track NMI nesting to separate per-CPU counter Boqun Feng
2026-08-07 7:01 ` [PATCH v5 02/18] preempt: Introduce HARDIRQ_DISABLE_BITS Boqun Feng
2026-08-07 7:02 ` [PATCH v5 03/18] preempt: Introduce __preempt_count_{sub,add}_return() Boqun Feng
2026-08-07 7:02 ` [PATCH v5 04/18] openrisc: Include <linux/cpumask.h> in smp.h Boqun Feng
2026-08-07 7:02 ` [PATCH v5 05/18] irq & spin_lock: Add counted interrupt disabling/enabling Boqun Feng
2026-08-07 7:02 ` [PATCH v5 06/18] irq: Add KUnit test for refcounted interrupt enable/disable Boqun Feng
2026-08-07 7:02 ` [PATCH v5 07/18] irq: Add max local_interrupt_disable() nesting level kunit test case Boqun Feng
2026-08-07 7:02 ` [PATCH v5 08/18] locking: Switch to _irq_{disable,enable}() variants in cleanup guards Boqun Feng
2026-08-07 7:02 ` [PATCH v5 09/18] sched: Remove the unused preempt_offset parameter of __cant_sleep() Boqun Feng
2026-08-07 7:02 ` [PATCH v5 10/18] sched: Avoid signed comparison of preempt_count() in __cant_migrate() Boqun Feng
2026-08-07 7:02 ` [PATCH v5 11/18] preempt: Introduce HAS_SEPARATE_PREEMPT_RESCHED_BITS Boqun Feng
2026-08-07 7:02 ` [PATCH v5 12/18] arm64: sched/preempt: Enable HAS_SEPARATE_PREEMPT_RESCHED_BITS Boqun Feng
2026-08-07 7:02 ` [PATCH v5 13/18] s390/preempt: " Boqun Feng
2026-08-07 7:02 ` [PATCH v5 14/18] rust: Introduce interrupt module Boqun Feng
2026-08-10 8:57 ` Peter Zijlstra
2026-08-10 13:28 ` Boqun Feng
2026-08-07 7:02 ` [PATCH v5 15/18] rust: helper: Add spin_{un,}lock_irq_{enable,disable}() helpers Boqun Feng
2026-08-07 7:02 ` [PATCH v5 16/18] rust: sync: Use super::* in spinlock.rs Boqun Feng
2026-08-07 7:02 ` [PATCH v5 17/18] rust: sync: Add SpinLockIrq Boqun Feng
2026-08-10 9:02 ` Peter Zijlstra
2026-08-10 13:21 ` Boqun Feng
2026-08-07 7:02 ` [PATCH v5 18/18] rust: sync: Introduce SpinLockIrq::lock_with() and friends Boqun Feng
2026-08-10 8:52 ` [PATCH v5 00/18] Refcounted interrupt disable and SpinLockIrq for Rust Peter Zijlstra
2026-08-10 8:53 ` Peter Zijlstra
2026-08-10 9:30 ` Peter Zijlstra
2026-08-10 10:38 ` Gary Guo
2026-08-10 10:49 ` Peter Zijlstra
2026-08-11 4:17 ` [PATCH 0/4] Improvements on SpinLockIrq patch series Boqun Feng
2026-08-11 4:17 ` [PATCH 1/4] irq: Add {over,under}flow detection for local_interrupt_{enable,disable} Boqun Feng
2026-08-11 4:17 ` [PATCH 2/4] selftests/bpf: Use the new NMI_BITS definition Boqun Feng
2026-08-11 4:17 ` Boqun Feng [this message]
2026-08-11 4:17 ` [PATCH 4/4] irq: Add max local_interrupt_disable() nesting level kunit test case Boqun Feng
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