linux-kernel - Re: [PATCH v6] ath9k: sleep for less time when unregistering hwrng

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Message-ID: <CAHmME9prgW60P+CO1JSdf5o1hBh8JtciBxcYm25ZO6oTCkwkxg@mail.gmail.com>
Date:   Tue, 28 Jun 2022 12:48:50 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Gregory Erwin <gregerwin256@...il.com>
Cc:     Toke Høiland-Jørgensen <toke@...hat.com>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kalle Valo <kvalo@...nel.org>,
        Rui Salvaterra <rsalvaterra@...il.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH v6] ath9k: sleep for less time when unregistering hwrng

On Tue, Jun 28, 2022 at 12:46 PM Jason A. Donenfeld <Jason@...c4.com> wrote:
>
> Hi Gregory,
>
> On Tue, Jun 28, 2022 at 3:39 AM Gregory Erwin <gregerwin256@...il.com> wrote:
> >
> > On Mon, Jun 27, 2022 at 5:18 AM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
> > >
> > > "Jason A. Donenfeld" <Jason@...c4.com> writes:
> > >
> > > > Even though hwrng provides a `wait` parameter, it doesn't work very well
> > > > when waiting for a long time. There are numerous deadlocks that emerge
> > > > related to shutdown. Work around this API limitation by waiting for a
> > > > shorter amount of time and erroring more frequently. This commit also
> > > > prevents hwrng from splatting messages to dmesg when there's a timeout
> > > > and switches to using schedule_timeout_interruptible(), so that the
> > > > kthread can be stopped.
> > > >
> > > > Reported-by: Gregory Erwin <gregerwin256@...il.com>
> > > > Tested-by: Gregory Erwin <gregerwin256@...il.com>
> > > > Cc: Toke Høiland-Jørgensen <toke@...hat.com>
> > > > Cc: Kalle Valo <kvalo@...nel.org>
> > > > Cc: Rui Salvaterra <rsalvaterra@...il.com>
> > > > Cc: Herbert Xu <herbert@...dor.apana.org.au>
> > > > Cc: stable@...r.kernel.org
> > > > Fixes: fcd09c90c3c5 ("ath9k: use hw_random API instead of directly dumping into random.c")
> > > > Link: https://lore.kernel.org/all/CAO+Okf6ZJC5-nTE_EJUGQtd8JiCkiEHytGgDsFGTEjs0c00giw@mail.gmail.com/
> > > > Link: https://lore.kernel.org/lkml/CAO+Okf5k+C+SE6pMVfPf-d8MfVPVq4PO7EY8Hys_DVXtent3HA@mail.gmail.com/
> > > > Link: https://bugs.archlinux.org/task/75138
> > > > Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> > >
> > > Gregory, care to take this version for a spin as well to double-check
> > > that it still resolves the issue? :)
> > >
> > > -Toke
> > >
> >
> > With patch v6, reads from /dev/hwrng block for 5-6s, during which 'ip link set
> > wlan0 down' will also block. Otherwise, 'ip link set wlan0 down' returns
> > immediately. Similarly, wiphy_suspend() consistently returns in under 10ms.
> >
> > Tested-by: Gregory Erwin <gregerwin256@...il.com>
>
> Oh 5-6s... so it's actually worse. Yikes. Sounds like v4 might have
> been the better patch, then?

$ curl https://lore.kernel.org/lkml/20220627104955.534013-1-Jason@zx2c4.com/raw
| git am

That one, if you want to give it a spin and see if that 5-6s is back
to ~1s or less.

Jason