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Date:   Thu, 13 Oct 2022 15:17:37 +1000
Message-Id: <CNKJHFYTRLX9.1OXK4PSAZ6J28@bobo>
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>,
        "Guenter Roeck" <linux@roeck-us.net>
Cc:     "Michael Ellerman" <mpe@ellerman.id.au>,
        "Linus Torvalds" <torvalds@linux-foundation.org>,
        <ajd@linux.ibm.com>, <aneesh.kumar@linux.ibm.com>,
        <atrajeev@linux.vnet.ibm.com>, <christophe.leroy@csgroup.eu>,
        <cuigaosheng1@huawei.com>, <david@redhat.com>,
        <farosas@linux.ibm.com>, <geoff@infradead.org>,
        <gustavoars@kernel.org>, <haren@linux.ibm.com>,
        <hbathini@linux.ibm.com>, <joel@jms.id.au>, <lihuafei1@huawei.com>,
        <linux-kernel@vger.kernel.org>, <linuxppc-dev@lists.ozlabs.org>,
        <lukas.bulwahn@gmail.com>, <mikey@neuling.org>,
        <nathan@kernel.org>, <nathanl@linux.ibm.com>,
        <nicholas@linux.ibm.com>, <pali@kernel.org>, <paul@paul-moore.com>,
        <rmclure@linux.ibm.com>, <ruscur@russell.cc>, <windhl@126.com>,
        <wsa+renesas@sang-engineering.com>, <ye.xingchen@zte.com.cn>,
        <yuanjilin@cdjrlc.com>, <zhengyongjun3@huawei.com>
Subject: Re: [GIT PULL] Please pull powerpc/linux.git powerpc-6.1-1 tag
From:   "Nicholas Piggin" <npiggin@gmail.com>
References: <87edvhntv0.fsf@mpe.ellerman.id.au>
 <20221012141827.GA2405914@roeck-us.net> <Y0biBtCUtc2mowbQ@zx2c4.com>
 <20221012164452.GA2990467@roeck-us.net> <Y0b3ZsTRHWG6jGK8@zx2c4.com>
 <20221012174826.GB2995920@roeck-us.net> <Y0cJfoPLGeuzm/gQ@zx2c4.com>
In-Reply-To: <Y0cJfoPLGeuzm/gQ@zx2c4.com>
Precedence: bulk

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.
> > >=20
> >=20
> > 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 =3D 0;
>         unsigned long last =3D random_get_entropy();
> +       return;
>
>         for (i =3D 0; i < NUM_TRIAL_SAMPLES - 1; ++i) {
>                 stack.entropy =3D 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