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Subject: Re: [PATCH v2 1/6] hwrng: core: Freeze khwrng thread during suspend
From:   Stephen Boyd <swboyd@chromium.org>
Cc:     Peter Huewe <peterhuewe@gmx.de>, linux-kernel@vger.kernel.org,
        Jason Gunthorpe <jgg@ziepe.ca>, Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-integrity@vger.kernel.org,
        Andrey Pronin <apronin@chromium.org>,
        Duncan Laurie <dlaurie@chromium.org>,
        Guenter Roeck <groeck@chromium.org>,
        Herbert Xu <herbert@gondor.apana.org.au>
To:     Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
User-Agent: alot/0.8.1
Date:   Fri, 02 Aug 2019 16:18:03 -0700
Sender: linux-kernel-owner@vger.kernel.org
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Quoting Jarkko Sakkinen (2019-08-02 13:22:09)
> On Tue, Jul 16, 2019 at 03:45:13PM -0700, Stephen Boyd wrote:
> > The hwrng_fill() function can run while devices are suspending and
> > resuming. If the hwrng is behind a bus such as i2c or SPI and that bus
> > is suspended, the hwrng may hang the bus while attempting to add some
> > randomness. It's been observed on ChromeOS devices with suspend-to-idle
> > (s2idle) and an i2c based hwrng that this kthread may run and ask the
> > hwrng device for randomness before the i2c bus has been resumed.
> >=20
> > Let's make this kthread freezable so that we don't try to touch the
> > hwrng during suspend/resume. This ensures that we can't cause the hwrng
> > backing driver to get into a bad state because the device is guaranteed
> > to be resumed before the hwrng kthread is thawed.
> >=20
> > Cc: Andrey Pronin <apronin@chromium.org>
> > Cc: Herbert Xu <herbert@gondor.apana.org.au>
> > Cc: Duncan Laurie <dlaurie@chromium.org>
> > Signed-off-by: Stephen Boyd <swboyd@chromium.org>
>=20
> This does not need a fixes tag?
>=20

I'll add Fixes: be4000bc4644 ("hwrng: create filler thread")