Re: Crashes with 874bbfe600a6 in 3.18.25

On Wed 03-02-16 11:59:01, Tejun Heo wrote:

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On Wed, Feb 03, 2016 at 05:48:52PM +0100, Michal Hocko wrote:

[...]

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anything and add_timer_on also for WORK_CPU_UNBOUND is really required
then we should at least preserve WORK_CPU_UNBOUND in dwork->cpu so that
__queue_work can actually move on to the local CPU properly and handle
the offline cpu properly.

delayed_work->cpu is determined on queueing time.  Dealing with
offlined cpus at execution is completley fine.  There's no need to
"preserve" anything.

I've seen you have posted a fix in the mean time but just for my
understading. Why the following is not an appropriate fix?

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index c579dbab2e36..52bb11cf20d1 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c

@@ -1459,9 +1459,9 @@ static void __queue_delayed_work(int cpu, struct workqueue_struct *wq,
 
 	dwork->wq = wq;
 	/* timer isn't guaranteed to run in this cpu, record earlier */
+	dwork->cpu = cpu;
 	if (cpu == WORK_CPU_UNBOUND)
 		cpu = raw_smp_processor_id();
-	dwork->cpu = cpu;
 	timer->expires = jiffies + delay;
 
 	add_timer_on(timer, cpu);