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

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Date:   Thu, 13 Oct 2022 15:17:37 +1000
From:   "Nicholas Piggin" <npiggin@...il.com>
To:     "Jason A. Donenfeld" <Jason@...c4.com>,
        "Guenter Roeck" <linux@...ck-us.net>
Cc:     "Michael Ellerman" <mpe@...erman.id.au>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        <ajd@...ux.ibm.com>, <aneesh.kumar@...ux.ibm.com>,
        <atrajeev@...ux.vnet.ibm.com>, <christophe.leroy@...roup.eu>,
        <cuigaosheng1@...wei.com>, <david@...hat.com>,
        <farosas@...ux.ibm.com>, <geoff@...radead.org>,
        <gustavoars@...nel.org>, <haren@...ux.ibm.com>,
        <hbathini@...ux.ibm.com>, <joel@....id.au>, <lihuafei1@...wei.com>,
        <linux-kernel@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>,
        <lukas.bulwahn@...il.com>, <mikey@...ling.org>,
        <nathan@...nel.org>, <nathanl@...ux.ibm.com>,
        <nicholas@...ux.ibm.com>, <pali@...nel.org>, <paul@...l-moore.com>,
        <rmclure@...ux.ibm.com>, <ruscur@...sell.cc>, <windhl@....com>,
        <wsa+renesas@...g-engineering.com>, <ye.xingchen@....com.cn>,
        <yuanjilin@...rlc.com>, <zhengyongjun3@...wei.com>
Subject: Re: [GIT PULL] Please pull powerpc/linux.git powerpc-6.1-1 tag

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