git: e2494f7561c8 - main - atomic: add atomic_interrupt_fence()

[Konstantin Belousov]

The branch main has been updated by kib:

URL: https://cgit.FreeBSD.org/src/commit/?id=e2494f7561c852951d8ac567314f5e12f19ee7af

commit e2494f7561c852951d8ac567314f5e12f19ee7af
Author:     Konstantin Belousov <kib at FreeBSD.org>
AuthorDate: 2021-02-23 22:12:29 +0000
Commit:     Konstantin Belousov <kib at FreeBSD.org>
CommitDate: 2021-02-24 20:45:24 +0000

    atomic: add atomic_interrupt_fence()
    
    with the semantic following C11 signal_fence, that is, it establishes
    ordering between its place and any interrupt handler executing on the
    same CPU.
    
    Reviewed by:    markj, mjg, rlibby
    Sponsored by:   The FreeBSD Foundation
    MFC after:      1 week
    Differential Revision:  https://reviews.freebsd.org/D28909
---
 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 39a4fa9c6f96..397a8fcd6b18 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 48f0a8b8939c..403b3de8a092 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