From 4ad87eee546ef97e3a5ad80414327f41f48a4e70 Mon Sep 17 00:00:00 2001 From: Boqun Feng Date: Tue, 4 Aug 2026 09:14:25 -0700 Subject: preempt: Introduce __preempt_count_{sub,add}_return() In order to use preempt_count() to track the interrupt disable nesting level, __preempt_count_{add,sub}_return() are introduced, as their names suggest, these primitives return the new value of the preempt_count() after changing it. The following example shows the usage of it in local_interrupt_disable(): // increase the HARDIRQ_DISABLE bit new_count = __preempt_count_add_return(HARDIRQ_DISABLE_OFFSET); // if it's the first-time increment, then disable the interrupt // at hardware level. if ((new_count & HARDIRQ_DISABLE_MASK) == HARDIRQ_DISABLE_OFFSET) { local_irq_save(flags); raw_cpu_write(local_interrupt_disable_state, flags); } Having these primitives will avoid a read of preempt_count() after changing preempt_count() on certain architectures. Signed-off-by: Boqun Feng Signed-off-by: Peter Zijlstra (Intel) Acked-by: Heiko Carstens # s390 Link: https://patch.msgid.link/20260804161447.84806-4-boqun@kernel.org --- include/asm-generic/preempt.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) (limited to 'include/asm-generic') diff --git a/include/asm-generic/preempt.h b/include/asm-generic/preempt.h index 51f8f3881523..c8683c046615 100644 --- a/include/asm-generic/preempt.h +++ b/include/asm-generic/preempt.h @@ -59,6 +59,20 @@ static __always_inline void __preempt_count_sub(int val) *preempt_count_ptr() -= val; } +static __always_inline int __preempt_count_add_return(int val) +{ + *preempt_count_ptr() += val; + + return *preempt_count_ptr(); +} + +static __always_inline int __preempt_count_sub_return(int val) +{ + *preempt_count_ptr() -= val; + + return *preempt_count_ptr(); +} + static __always_inline bool __preempt_count_dec_and_test(void) { /* -- cgit