On Tue, Jun 23, 2015 at 12:21:52AM +0200, Oleg Nesterov wrote:
> Suppose that stop_two_cpus(cpu1 => 0, cpu2 => 1) races with stop_machine().
>
> - stop_machine takes the lock on CPU 0, adds the work
> and drops the lock
>
> - cpu_stop_queue_work() queues both works
cpu_stop_queue_work() only ever queues _1_ work.
> - stop_machine takes the lock on CPU 1, etc
>
> In this case both CPU 0 and 1 will run multi_cpu_stop() but they will
> use different multi_stop_data's, so they will wait for each other
> forever?
So what you're saying is:
queue_stop_cpus_work() stop_two_cpus()
cpu_stop_queue_work(0,..);
spin_lock(0);
spin_lock(1);
__cpu_stop_queue_work(0,..);
__cpu_stop_queue_work(1,..);
spin_unlock(1);
spin_unlock(0);
cpu_stop_queue_work(1,..);
Indeed, I don't know what I was thinking...
We can of course slap a percpu-rwsem in, but I wonder if there's
anything smarter we can do here.
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