CVS commit: src/sys/dev

[Taylor R Campbell]

Module Name:    src
Committed By:   riastradh
Date:           Sat Sep 24 11:06:03 UTC 2022

Modified Files:
        src/sys/dev: efi.c

Log Message:
efi(4): Fix access to efi_isopen.

- Qualify efi_isopen with volatile.
- Ensure open has acquire ordering and close has release ordering.
- Use atomic_swap, not atomic_cas -- simpler and may be cheaper.
- Use atomic_store, not atomic_swap -- simpler and usually cheaper.

(Could maybe just use __cpu_simple_lock to avoid having to write out
these details.)


To generate a diff of this commit:
cvs rdiff -u -r1.3 -r1.4 src/sys/dev/efi.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.


Modified files:

Index: src/sys/dev/efi.c
diff -u src/sys/dev/efi.c:1.3 src/sys/dev/efi.c:1.4
--- src/sys/dev/efi.c:1.3	Fri Apr  1 06:51:12 2022
+++ src/sys/dev/efi.c	Sat Sep 24 11:06:03 2022
@@ -1,4 +1,4 @@
-/* $NetBSD: efi.c,v 1.3 2022/04/01 06:51:12 skrll Exp $ */
+/* $NetBSD: efi.c,v 1.4 2022/09/24 11:06:03 riastradh Exp $ */
 
 /*-
  * Copyright (c) 2021 Jared McNeill <jmcne...@invisible.ca>
@@ -32,7 +32,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: efi.c,v 1.3 2022/04/01 06:51:12 skrll Exp $");
+__KERNEL_RCSID(0, "$NetBSD: efi.c,v 1.4 2022/09/24 11:06:03 riastradh Exp $");
 
 #include <sys/param.h>
 #include <sys/conf.h>
@@ -78,7 +78,7 @@ static const struct efi_ops *efi_ops = N
  * that a SetVariable() call between calls to GetNextVariableName() may
  * produce unpredictable results, and we want to avoid this.
  */
-static u_int efi_isopen = 0;
+static volatile u_int efi_isopen = 0;
 
 static dev_type_open(efi_open);
 static dev_type_close(efi_close);
@@ -102,20 +102,23 @@ const struct cdevsw efi_cdevsw = {
 static int
 efi_open(dev_t dev, int flags, int type, struct lwp *l)
 {
+
 	if (efi_ops == NULL) {
 		return ENXIO;
 	}
-	if (atomic_cas_uint(&efi_isopen, 0, 1) == 1) {
+	if (atomic_swap_uint(&efi_isopen, 1) == 1) {
 		return EBUSY;
 	}
+	membar_acquire();
 	return 0;
 }
 
 static int
 efi_close(dev_t dev, int flags, int type, struct lwp *l)
 {
+
 	KASSERT(efi_isopen);
-	atomic_swap_uint(&efi_isopen, 0);
+	atomic_store_release(&efi_isopen, 0);
 	return 0;
 }