linux-kernel - Re: 2.6.21-rc7-mm1: BUG_ON in kthread_bind during _cpu

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Message-Id: <20070425165410.b73443b4.akpm@linux-foundation.org>
Date:	Wed, 25 Apr 2007 16:54:10 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Gautham R Shenoy <ego@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...sign.ru>
Subject: Re: 2.6.21-rc7-mm1: BUG_ON in kthread_bind during _cpu_down

On Thu, 26 Apr 2007 01:10:21 +0200 "Rafael J. Wysocki" <rjw@...k.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);
_

-
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