As the name suggests, remrunqueue(p) removes p from its run queue, and
I believe that makes TAILQ_FOREACH() here unsafe. Instead of actually
removing all threads from the processor, we'll only remove the first
from each of its run queues.
Diff below replaces TAILQ_FOREACH with the safe/idiomatic pattern for
draining a queue.
ok?
(This hasn't bit me and I don't know any practical consequences of it.
Just spotted it while tracking down a bug in a kern_synch.c diff I'm
working on.)
Index: kern_sched.c
===================================================================
RCS file: /cvs/src/sys/kern/kern_sched.c,v
retrieving revision 1.32
diff -u -p -r1.32 kern_sched.c
--- kern_sched.c 4 May 2014 05:03:26 -0000 1.32
+++ kern_sched.c 13 Jul 2014 20:18:38 -0000
@@ -272,7 +272,7 @@ sched_chooseproc(void)
if (spc->spc_schedflags & SPCF_SHOULDHALT) {
if (spc->spc_whichqs) {
for (queue = 0; queue < SCHED_NQS; queue++) {
- TAILQ_FOREACH(p, &spc->spc_qs[queue], p_runq) {
+ while ((p = TAILQ_FIRST(&spc->spc_qs[queue]))) {
remrunqueue(p);
p->p_cpu = sched_choosecpu(p);
setrunqueue(p);
