linux-kernel - Re: [PATCH v2 1/2] random: move add_hwgenerator

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Date:   Mon, 19 Sep 2022 13:19:39 -0400
From:   Sven van Ashbrook <svenva@...omium.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Dominik Brodowski <linux@...inikbrodowski.net>,
        Peter Huewe <peterhuewe@....de>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Olivia Mackall <olivia@...enic.com>,
        Alex Levin <levinale@...gle.com>,
        Andrey Pronin <apronin@...gle.com>,
        Stephen Boyd <swboyd@...gle.com>,
        Rajat Jain <rajatja@...gle.com>,
        Eric Biggers <ebiggers@...gle.com>,
        Petr Mladek <pmladek@...e.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "Theodore Ts'o" <tytso@....edu>, linux-crypto@...r.kernel.org
Subject: Re: [PATCH v2 1/2] random: move add_hwgenerator_randomness()'s wait
 outside function

On Mon, Sep 19, 2022 at 11:06 AM Jason A. Donenfeld <Jason@...c4.com> wrote:
>
> By the way, there was a recent ath9k patch that kind of went to a
> similar tune. [...] Maybe that's a potential solution here, or
> something similar to it.

Jason was kind enough to point me to the patch in question:
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=36cb6494429bd64b27b7ff8b4af56f8e526da2b4

This patch limits the long sleep inside the fillfn kthread, by
terminating the sleep on
hwrng_unregister().

This doesn't appear like a viable approach for the suspend/resume issue?
- there is a great multitude of tpm_msleep()/msleep() calls in the tpm's
  rng_get_data() path. They would all have to be made interruptible.
- even if interrupted successfully, now the kthread must be blocked until
  after resume. If so, what is the point of using a non-freezable kthread.