On Mon, Jul 30, 2018 at 10:12:43AM -0700, Sodagudi Prasad wrote:
> How about including below change as well? Currently, there is no way to
> identify thread migrations completed or not. When we observe this issue,
> the symptom was work queue lock up. It is better to have some timeout here
> and induce the bug_on.
You'd trigger the soft-lockup or hung-task detector I think. And if not,
we ought to look at making it trigger at least one of those.
> There is no way to identify the migration threads stuck or not.
Should be pretty obvious from the splat generated by the above, no?
> --- a/kernel/stop_machine.c
> +++ b/kernel/stop_machine.c
> @@ -290,6 +290,7 @@ int stop_two_cpus(unsigned int cpu1, unsigned int cpu2,
> cpu_stop_fn_t fn, void *
> struct cpu_stop_done done;
> struct cpu_stop_work work1, work2;
> struct multi_stop_data msdata;
> + int ret;
>
> msdata = (struct multi_stop_data){
> .fn = fn,
> @@ -312,7 +313,10 @@ int stop_two_cpus(unsigned int cpu1, unsigned int cpu2,
> cpu_stop_fn_t fn, void *
> if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2))
> return -ENOENT;
>
> - wait_for_completion(&done.completion);
> + ret = wait_for_completion_timeout(&done.completion,
> msecs_to_jiffies(1000));
> + if (!ret)
> + BUG_ON(1);
> +
That's a random timeout, which if you spuriously trigger it, will take
down your machine. That seems like a cure worse than the disease.
