linux-kernel - Re: [Bug #11989] Suspend failure on NForce4-based boards due to chanes in stop

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Message-Id: <200811112256.58467.rusty@rustcorp.com.au>
Date:	Wed, 12 Nov 2008 14:09:49 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Vegard Nossum <vegard.nossum@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Oleg Nesterov <oleg@...hat.com>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [Bug #11989] Suspend failure on NForce4-based boards due to chanes in stop_machine

On Tuesday 11 November 2008 21:22:14 Ingo Molnar wrote:
> * Rafael J. Wysocki <rjw@...k.pl> wrote:
> > So, it evidently fails while re-enabling the non-boot CPU and not
> > during disabling it as I thought before.

(Resend, due to HTML version previously)

But what is calling stop_machine in that path?

There *is* a race, but I don't think it could cause this (we should make a
copy of active.fnret inside the lock before returning it).

Two patches: one fixes that race, the next adds debugging spew.

stop_machine: fix race with return value

We should not access active.fnret outside the lock; in theory the next
stop_machine could overwrite it.

Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
---
 kernel/stop_machine.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff -r d7c9a15da615 kernel/stop_machine.c
--- a/kernel/stop_machine.c	Mon Nov 10 09:47:45 2008 +1100
+++ b/kernel/stop_machine.c	Tue Nov 11 23:19:47 2008 +1030
@@ -112,7 +112,7 @@
 int __stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus)
 {
 	struct work_struct *sm_work;
-	int i;
+	int i, ret;
 
 	/* Set up initial state. */
 	mutex_lock(&lock);
@@ -137,8 +137,9 @@
 	/* This will release the thread on our CPU. */
 	put_cpu();
 	flush_workqueue(stop_machine_wq);
+	ret = active.fnret;
 	mutex_unlock(&lock);
-	return active.fnret;
+	return ret;
 }
 
 int stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus)
===
diff -r fe7dd39b1cff kernel/stop_machine.c
--- a/kernel/stop_machine.c	Wed Nov 12 14:07:18 2008 +1030
+++ b/kernel/stop_machine.c	Wed Nov 12 14:09:08 2008 +1030
@@ -89,6 +89,8 @@
 			case STOPMACHINE_RUN:
 				/* On multiple CPUs only a single error code
 				 * is needed to tell that something failed. */
+				printk("stop_machine: %i running %p\n",
+				       smp_processor_id(), smdata->fn);
 				err = smdata->fn(smdata->data);
 				if (err)
 					smdata->fnret = err;
@@ -106,6 +108,7 @@
 /* Callback for CPUs which aren't supposed to do anything. */
 static int chill(void *unused)
 {
+	printk("stop_machine: %i chilling\n", smp_processor_id());
 	return 0;
 }
 
@@ -126,17 +129,23 @@
 
 	set_state(STOPMACHINE_PREPARE);
 
+	printk("stop_machine: running on %i cpus:\n", num_threads);
+	dump_stack();
+
 	/* Schedule the stop_cpu work on all cpus: hold this CPU so one
 	 * doesn't hit this CPU until we're ready. */
 	get_cpu();
 	for_each_online_cpu(i) {
+		printk("stop_machine: setting up cpu %i\n", i);
 		sm_work = percpu_ptr(stop_machine_work, i);
 		INIT_WORK(sm_work, stop_cpu);
 		queue_work_on(i, stop_machine_wq, sm_work);
 	}
 	/* This will release the thread on our CPU. */
+	printk("stop_machine: releasing CPU %i\n", smp_processor_id());
 	put_cpu();
 	flush_workqueue(stop_machine_wq);
+	printk("stop_machine: done\n");
 	ret = active.fnret;
 	mutex_unlock(&lock);
 	return ret;
.