Module Name: src
Committed By: ad
Date: Sun Feb 16 21:31:19 UTC 2020
Modified Files:
src/sys/kern: kern_synch.c
Log Message:
nextlwp(): fix a couple of locking bugs including one I introduced yesterday,
and add comments around same.
To generate a diff of this commit:
cvs rdiff -u -r1.339 -r1.340 src/sys/kern/kern_synch.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/kern/kern_synch.c
diff -u src/sys/kern/kern_synch.c:1.339 src/sys/kern/kern_synch.c:1.340
--- src/sys/kern/kern_synch.c:1.339 Sat Feb 15 18:12:15 2020
+++ src/sys/kern/kern_synch.c Sun Feb 16 21:31:19 2020
@@ -1,7 +1,7 @@
-/* $NetBSD: kern_synch.c,v 1.339 2020/02/15 18:12:15 ad Exp $ */
+/* $NetBSD: kern_synch.c,v 1.340 2020/02/16 21:31:19 ad Exp $ */
/*-
- * Copyright (c) 1999, 2000, 2004, 2006, 2007, 2008, 2009, 2019
+ * Copyright (c) 1999, 2000, 2004, 2006, 2007, 2008, 2009, 2019, 2020
* The NetBSD Foundation, Inc.
* All rights reserved.
*
@@ -69,7 +69,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_synch.c,v 1.339 2020/02/15 18:12:15 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_synch.c,v 1.340 2020/02/16 21:31:19 ad Exp $");
#include "opt_kstack.h"
#include "opt_dtrace.h"
@@ -476,23 +476,34 @@ nextlwp(struct cpu_info *ci, struct sche
* Let sched_nextlwp() select the LWP to run the CPU next.
* If no LWP is runnable, select the idle LWP.
*
- * Note that spc_lwplock might not necessary be held, and
- * new thread would be unlocked after setting the LWP-lock.
+ * On arrival here LWPs on a run queue are locked by spc_mutex which
+ * is currently held. Idle LWPs are always locked by spc_lwplock,
+ * which may or may not be held here. On exit from this code block,
+ * in all cases newl is locked by spc_lwplock.
*/
newl = sched_nextlwp();
if (newl != NULL) {
sched_dequeue(newl);
KASSERT(lwp_locked(newl, spc->spc_mutex));
KASSERT(newl->l_cpu == ci);
- lwp_setlock(newl, spc->spc_lwplock);
+ newl->l_stat = LSONPROC;
+ newl->l_pflag |= LP_RUNNING;
+ spc->spc_curpriority = lwp_eprio(newl);
spc->spc_flags &= ~(SPCF_SWITCHCLEAR | SPCF_IDLE);
+ lwp_setlock(newl, spc->spc_lwplock);
} else {
+ /*
+ * Updates to newl here are unlocked, but newl is the idle
+ * LWP and thus sheltered from outside interference, so no
+ * harm is going to come of it.
+ */
newl = ci->ci_data.cpu_idlelwp;
+ newl->l_stat = LSONPROC;
+ newl->l_pflag |= LP_RUNNING;
+ spc->spc_curpriority = PRI_IDLE;
spc->spc_flags = (spc->spc_flags & ~SPCF_SWITCHCLEAR) |
SPCF_IDLE;
}
- newl->l_stat = LSONPROC;
- newl->l_pflag |= LP_RUNNING;
/*
* Only clear want_resched if there are no pending (slow) software
@@ -502,7 +513,6 @@ nextlwp(struct cpu_info *ci, struct sche
* the release of spc_mutex becomes globally visible.
*/
ci->ci_want_resched = ci->ci_data.cpu_softints;
- spc->spc_curpriority = lwp_eprio(newl);
return newl;
}
