Re: 2.6.21-rc7-mm1: BUG_ON in kthread_bind during _cpu_down

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 26 Apr 2007 01:10:21 +0200 "Rafael J. Wysocki" <rjw@sisk.pl> wrote:

> Hi,
> 
> The BUG_ON in khthread_bind (line 165 in kthread.c) triggers for me during
> attempted suspend to disk, when disable_nonboot_cpus() calls _cpu_down()
> (on x86_64).

I guess the backtrace would be pretty important here.

Guys, please don't add BUG_ONs unless there is simply no sane way to recover.

Because when someone goofs up, the BUG_ON will kill the whole machine and
everyone else who has code being tested in -mm loses a tester.

Plus a BUG_ON *greatly* decreases our chances of getting a trace from the
tester: dead box, nothing in the logs.


--- a/kernel/kthread.c~fix-kthread_create-vs-freezer-theoretical-race-dont-be-obnoxious
+++ a/kernel/kthread.c
@@ -162,7 +162,10 @@ EXPORT_SYMBOL(kthread_create);
  */
 void kthread_bind(struct task_struct *k, unsigned int cpu)
 {
-	BUG_ON(k->state != TASK_UNINTERRUPTIBLE);
+	if (k->state != TASK_UNINTERRUPTIBLE) {
+		WARN_ON(1);
+		return;
+	}
 	/* Must have done schedule() in kthread() before we set_task_cpu */
 	wait_task_inactive(k);
 	set_task_cpu(k, cpu);
_