[src/trunk]: src/sys/kern select(9): Use membar_acquire/release and atomic_st...

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/d6cbfab0148a
branches:  trunk
changeset: 365175:d6cbfab0148a
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Sat Apr 09 23:52:05 2022 +0000

description:
select(9): Use membar_acquire/release and atomic_store_release.

No store-before-load ordering here -- this was obviously always
intended to be load-before-load/store all along.

diffstat:

 sys/kern/sys_select.c |  11 +++++------
 1 files changed, 5 insertions(+), 6 deletions(-)

diffs (47 lines):

diff -r 78cda3b9a90c -r d6cbfab0148a sys/kern/sys_select.c
--- a/sys/kern/sys_select.c     Sat Apr 09 23:51:57 2022 +0000
+++ b/sys/kern/sys_select.c     Sat Apr 09 23:52:05 2022 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: sys_select.c,v 1.58 2022/02/12 15:51:29 thorpej Exp $  */
+/*     $NetBSD: sys_select.c,v 1.59 2022/04/09 23:52:05 riastradh Exp $        */
 
 /*-
  * Copyright (c) 2007, 2008, 2009, 2010, 2019, 2020 The NetBSD Foundation, Inc.
@@ -84,7 +84,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: sys_select.c,v 1.58 2022/02/12 15:51:29 thorpej Exp $");
+__KERNEL_RCSID(0, "$NetBSD: sys_select.c,v 1.59 2022/04/09 23:52:05 riastradh Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -282,7 +282,7 @@
                        l->l_selflag = SEL_SCANNING;
                }
                ncoll = sc->sc_ncoll;
-               membar_exit();
+               membar_release();
 
                if (opname == selop_select) {
                        error = selscan((char *)fds, nf, ni, retval);
@@ -653,7 +653,7 @@
                 * barrier to ensure that we access sel_lwp (above) before
                 * other fields - this guards against a call to selclear().
                 */
-               membar_enter();
+               membar_acquire();
                sip->sel_lwp = selector;
                SLIST_INSERT_HEAD(&selector->l_selwait, sip, sel_chain);
                /* Copy the argument, which is for selnotify(). */
@@ -872,9 +872,8 @@
                 * globally visible.
                 */
                next = SLIST_NEXT(sip, sel_chain);
-               membar_exit();
                /* Release the record for another named waiter to use. */
-               sip->sel_lwp = NULL;
+               atomic_store_release(&sip->sel_lwp, NULL);
        }
        mutex_spin_exit(lock);
 }