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Date:   Fri, 24 Jun 2022 02:50:26 +0200
From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
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>
Subject: Re: ath9k: hwrng blocks for several minutes when phy is un-associated
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Hey again again,

On Fri, Jun 24, 2022 at 02:01:22AM +0200, Jason A. Donenfeld wrote:
> 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.

I think I have a plausible theory. I'll send a real patch, and you can
test it. Incoming shortly...

Jason