From f279cbcbdf765cb1f3e419605efeb3c397b6c806 Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Wed, 24 Feb 2021 00:12:29 +0200
Subject: [PATCH] atomic: add atomic_interrupt_fence()

Approved by:	re (gjb)

(cherry picked from commit e2494f7561c852951d8ac567314f5e12f19ee7af)
---
 share/man/man9/atomic.9 | 13 ++++++++++++-
 sys/sys/atomic_common.h |  2 ++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/share/man/man9/atomic.9 b/share/man/man9/atomic.9
index 39a4fa9c6f9..397a8fcd6b1 100644
--- a/share/man/man9/atomic.9
+++ b/share/man/man9/atomic.9
@@ -22,7 +22,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd August 18, 2019
+.Dd February 24, 2021
 .Dt ATOMIC 9
 .Os
 .Sh NAME
@@ -31,6 +31,7 @@
 .Nm atomic_cmpset ,
 .Nm atomic_fcmpset ,
 .Nm atomic_fetchadd ,
+.Nm atomic_interrupt_fence ,
 .Nm atomic_load ,
 .Nm atomic_readandclear ,
 .Nm atomic_set ,
@@ -59,6 +60,8 @@
 .Fc
 .Ft <type>
 .Fn atomic_fetchadd_<type> "volatile <type> *p" "<type> v"
+.Ft void
+.Fn atomic_interrupt_fence "void"
 .Ft <type>
 .Fn atomic_load_[acq_]<type> "volatile <type> *p"
 .Ft <type>
@@ -292,6 +295,14 @@ release stores, by separating access from ordering, they can sometimes
 facilitate more efficient implementations of synchronization primitives.
 For example, they can be used to avoid executing a memory barrier until a
 memory access shows that some condition is satisfied.
+.Ss Interrupt Fence Operations
+The
+.Fn atomic_interrupt_fence()
+function establishes ordering between its call location and any interrupt
+handler executing on the same CPU.
+It is modeled after the similar C11 function
+.Fn atomic_signal_fence() ,
+and adapted for the kernel environment.
 .Ss Multiple Processors
 In multiprocessor systems, the atomicity of the atomic operations on memory
 depends on support for cache coherence in the underlying architecture.
diff --git a/sys/sys/atomic_common.h b/sys/sys/atomic_common.h
index 48f0a8b8939..403b3de8a09 100644
--- a/sys/sys/atomic_common.h
+++ b/sys/sys/atomic_common.h
@@ -78,4 +78,6 @@
 #define	atomic_load_consume_ptr(p)	\
     ((__typeof(*p)) atomic_load_acq_ptr((uintptr_t *)p))
 
+#define	atomic_interrupt_fence()	__compiler_membar()
+
 #endif
-- 
2.45.0