Linus,
Attached is a resend of a patch to fix a race in migration_thread which
results in a deadlock on boot for some SMP systems. The fix is to to
disable preemption inside of set_cpus_allowed.
Andrew Morton first noticed the problem and provided the following patch
a few weeks back. I was not affected until the recent migration_init
fix, for some odd reason. Neither Andrew nor I think this is actually
kernel preemption's fault but perhaps a race in the tricky behavior of
the migration code.
Patch is against 2.5.8, please apply.
Robert Love
diff -urN linux-2.5.8/kernel/sched.c linux/kernel/sched.c
--- linux-2.5.8/kernel/sched.c Sun Apr 14 15:18:47 2002
+++ linux/kernel/sched.c Mon Apr 15 14:47:18 2002
@@ -1649,6 +1649,7 @@
if (!new_mask)
BUG();
+ preempt_disable();
rq = task_rq_lock(p, &flags);
p->cpus_allowed = new_mask;
/*
@@ -1657,7 +1658,7 @@
*/
if (new_mask & (1UL << p->thread_info->cpu)) {
task_rq_unlock(rq, &flags);
- return;
+ goto out;
}
init_MUTEX_LOCKED(&req.sem);
@@ -1667,6 +1668,8 @@
wake_up_process(rq->migration_thread);
down(&req.sem);
+out:
+ preempt_enable();
}
static volatile unsigned long migration_mask;
-
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This archive was generated by hypermail 2b29 : Mon Apr 15 2002 - 22:00:25 EST