Module Name: src
Committed By: ozaki-r
Date: Fri Feb 16 07:04:51 UTC 2018
Modified Files:
src/sys/kern: kern_synch.c
Log Message:
Avoid a race condition between an LWP migration and curlwp_bind
curlwp_bind sets the LP_BOUND flag to l_pflags of the current LWP, which
prevents it from migrating to another CPU until curlwp_bindx is called.
Meanwhile, there are several ways that an LWP is migrated to another CPU and in
any cases the scheduler postpones a migration if a target LWP is running. One
example of LWP migrations is a load balancing; the scheduler periodically
explores CPU-hogging LWPs and schedule them to migrate (see sched_lwp_stats).
At that point the scheduler checks the LP_BOUND flag and if it's set to a LWP,
the scheduler doesn't schedule the LWP. A scheduled LWP is tried to be migrated
when it is leaving a running CPU, i.e., mi_switch. And mi_switch does NOT check
the LP_BOUND flag. So if an LWP is scheduled first and then it sets the
LP_BOUND flag, the LWP can be migrated regardless of the flag. To avoid this
race condition, we need to check the flag in mi_switch too.
For more details see
https://mail-index.netbsd.org/tech-kern/2018/02/13/msg023079.html
To generate a diff of this commit:
cvs rdiff -u -r1.313 -r1.314 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:1.313 src/sys/kern/kern_synch.c:1.314
--- src/sys/kern/kern_synch.c:1.313 Tue Jan 30 07:52:22 2018
+++ src/sys/kern/kern_synch.c Fri Feb 16 07:04:51 2018
@@ -1,4 +1,4 @@
-/* $NetBSD: kern_synch.c,v 1.313 2018/01/30 07:52:22 ozaki-r Exp $ */
+/* $NetBSD: kern_synch.c,v 1.314 2018/02/16 07:04:51 ozaki-r Exp $ */
/*-
* Copyright (c) 1999, 2000, 2004, 2006, 2007, 2008, 2009
@@ -69,7 +69,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_synch.c,v 1.313 2018/01/30 07:52:22 ozaki-r Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_synch.c,v 1.314 2018/02/16 07:04:51 ozaki-r Exp $");
#include "opt_kstack.h"
#include "opt_perfctrs.h"
@@ -589,7 +589,8 @@ mi_switch(lwp_t *l)
* be reset here, if interrupt/preemption happens
* early in idle LWP.
*/
- if (l->l_target_cpu != NULL) {
+ if (l->l_target_cpu != NULL &&
+ (l->l_pflag & LP_BOUND) == 0) {
KASSERT((l->l_pflag & LP_INTR) == 0);
spc->spc_migrating = l;
}
