Received-SPF: pass (google.com: domain of linux-crypto-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <CAO+Okf6ZJC5-nTE_EJUGQtd8JiCkiEHytGgDsFGTEjs0c00giw@mail.gmail.com>
 <YrRZLPQHK0QbLTjr@zx2c4.com> <YrRZoGBMBa3lFkwx@zx2c4.com> <CAO+Okf5JbZ7vUeXWMOZU9Fz=igoVBOZZAiWn7w7SxW5t+dO0Ag@mail.gmail.com>
 <CAHmME9otPsJz5WUq_S2NuJFy0RzjUKEaU=4mZx-dAgfJF8P-yQ@mail.gmail.com>
In-Reply-To: <CAHmME9otPsJz5WUq_S2NuJFy0RzjUKEaU=4mZx-dAgfJF8P-yQ@mail.gmail.com>
From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
Date:   Fri, 24 Jun 2022 02:01:22 +0200
Message-ID: <CAHmME9oAV+YbtfYh+h1OBpjTnJJzyfAujuCC1BSKMwsH8hDx0w@mail.gmail.com>
Subject: Re: ath9k: hwrng blocks for several minutes when phy is un-associated
To:     Gregory Erwin <gregerwin256@gmail.com>
Cc:     Rui Salvaterra <rsalvaterra@gmail.com>,
        Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
        linux-wireless <linux-wireless@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Hey again,

On Fri, Jun 24, 2022 at 1:47 AM Jason A. Donenfeld <Jason@zx2c4.com> wrote:
>
> Hey Gregory,
>
> On Fri, Jun 24, 2022 at 1:36 AM Gregory Erwin <gregerwin256@gmail.com> wrote:
> >
> > No luck.
> >
> > The first patch caused a warning and oops with ath9k_rng_read() at the
> > top of the call stack when reading from /dev/hwrng:
> >   WARNING: CPU: 1 PID: 454 at kernel/kthread.c:75 kthread_should_stop+0x2a/0x30
> >   BUG: kernel NULL pointer dereference, address: 0000000000000000
> >
> > The second didn't have a noticeable effect, for better or worse.
>
> Alright. That's actually getting us somewhere. So the path in question
> here is from reading /dev/hwrng, not from the kthread that's doing the
> same read.
>
> Can you do a `cat /dev/hwrng > /dev/null`, and then do whatever it is
> you do that causes everything to hang, and then while things are hung
> in the bad way, look at the contents of /proc/[the pid of the cat you
> just ran]/stack?

There's another flow I'm interested in. You said it prevents the
system from sleeping. Does it also make a `ip link set wlan0 down`
hang too? If so, could you send the `/proc/[pid of ip link set
down]/stack ` of a hung ip process? That seems like the more relevant
deadlock to look into.

Jason