Re: [PATCH] random: fix possible sleeping allocation from irq context

Tetsuo Handa
2018-04-25T10:47:27Z

Theodore Y. Ts'o wrote:
> On Wed, Apr 25, 2018 at 09:46:42AM +0900, Tetsuo Handa wrote:
> > Theodore Ts'o wrote:
> > > We can do a sleeping allocation from an irq context when CONFIG_NUMA
> > > is enabled. Fix this by initializing the NUMA crng instances in a
> > > workqueue.
> >
> > Offloading to workqueue context itself would be OK,
> > but this patch makes linux.git unbootable because
> >
> > if (crng == &primary_crng && crng_init < 2) {
> > invalidate_batched_entropy();
> > numa_crng_init(); // <= Deferred to workqueue context.
> > crng_init = 2; // <= Not waiting for workqueue context, and oops before console becomes ready. ;-)
> > process_random_ready_list();
> > wake_up_interruptible(&crng_init_wait);
> > pr_notice("random: crng init done\n");
> > }
> >
> > Please don't pretend rng_ready() before workqueue context is processed.
>
> Where's the oops?

I assumed an oops happened, for the kernel did not start printing messages even
after 1 minute from guest's power on, and CPU usage (seen from host side) says
that 1 CPU is busy-looping; which is a phenomenon that the kernel panic()ed at
very early stage. And reverting only your patch solved the problem.

But I can no longer reproduce it. I should have saved the kernel config...
So, if nobody sees regression, please go with your patch.

-DECLARE_WORK(numa_crng_init_work, do_numa_crng_init);
+static DECLARE_WORK(numa_crng_init_work, do_numa_crng_init);