Re: [GIT PULL] Please pull powerpc/linux.git powerpc-6.1-1 tag

[Nicholas Piggin]

On Thu Oct 13, 2022 at 4:37 AM AEST, Jason A. Donenfeld wrote:
> On Wed, Oct 12, 2022 at 10:48:26AM -0700, Guenter Roeck wrote:
> > > I've also managed to not hit this bug a few times. When it triggers,
> > > after "kprobes: kprobe jump-optimization is enabled. All kprobes are
> > > optimized if possible.", there's a long hang - tens seconds before it
> > > continues. When it doesn't trigger, there's no hang at that point in the
> > > boot process.
> > > 
> > 
> > That probably explains why my attempts to bisect the problem were
> > unsuccessful.
>
> So I just did this:
>
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index 2fe28eeb2f38..2d70bc09db7e 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -1212,6 +1212,7 @@ static void __cold try_to_generate_entropy(void)
>         struct entropy_timer_state stack;
>         unsigned int i, num_different = 0;
>         unsigned long last = random_get_entropy();
> +       return;
>
>         for (i = 0; i < NUM_TRIAL_SAMPLES - 1; ++i) {
>                 stack.entropy = random_get_entropy();
>
> And then ran it, and now we get the lockup from the idle process:

Yep that rules out the random code. And really if it was calling
schedule() it shouldn't be getting a softlockup anyway.

Thanks,
Nick