Re: [PATCH] kthread: Prevent unpark race which puts threads on the wrong cpu

From: Thomas Gleixner <tglx@linutronix.de>
To: Dave Hansen <dave@sr71.net>
Cc: Borislav Petkov <bp@alien8.de>,
	"Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Dave Jones <davej@redhat.com>,
	dhillf@gmail.com, Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH] kthread: Prevent unpark race which puts threads on the wrong cpu
Date: Wed, 10 Apr 2013 10:29:45 +0200 (CEST)	[thread overview]
Message-ID: <alpine.LFD.2.02.1304101024010.21884@ionos> (raw)
In-Reply-To: <51647C30.3050109@sr71.net>

On Tue, 9 Apr 2013, Dave Hansen wrote:

> On 04/09/2013 12:30 PM, Thomas Gleixner wrote:
> > On Tue, 9 Apr 2013, Thomas Gleixner wrote:
> > Thought more about it and found, that the stupid binding only works
> > when the task is really descheduled. So there is a small window left,
> > which could lead to this. Revised patch below.
> > 
> > Anyway a trace for that issue would be appreciated nevertheless.
> 
> Here you go:
> 
> 	http://sr71.net/~dave/linux/bigbox.1365539189.txt.gz

Hmm. Unfortunately migration/146 is not in the trace.
 
Can you please apply the patch below? That avoids the oops, but might
hang an online operation. Though the machine should stay up and you
should be able to retrieve the trace.

Thanks,

	tglx
---
Index: linux-2.6/kernel/smpboot.c
===================================================================

--- linux-2.6.orig/kernel/smpboot.c
+++ linux-2.6/kernel/smpboot.c
@@ -131,7 +131,10 @@ static int smpboot_thread_fn(void *data)
 			continue;
 		}
 
-		BUG_ON(td->cpu != smp_processor_id());
+		if (td->cpu != smp_processor_id()) {
+			tracing_off();
+			schedule();
+		}
 
 		/* Check for state change setup */
 		switch (td->status) {
