linux-kernel - Re: [PATCH v2 1/6] hwrng: core: Freeze khwrng thread during suspend

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Message-ID: <20190802202209.2jzeosacc66mtnpr@linux.intel.com>
Date:   Fri, 2 Aug 2019 23:22:09 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Peter Huewe <peterhuewe@....de>, linux-kernel@...r.kernel.org,
        Jason Gunthorpe <jgg@...pe.ca>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-integrity@...r.kernel.org,
        Andrey Pronin <apronin@...omium.org>,
        Duncan Laurie <dlaurie@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [PATCH v2 1/6] hwrng: core: Freeze khwrng thread during suspend

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.
> 
> 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.
> 
> Cc: Andrey Pronin <apronin@...omium.org>
> Cc: Herbert Xu <herbert@...dor.apana.org.au>
> Cc: Duncan Laurie <dlaurie@...omium.org>
> Signed-off-by: Stephen Boyd <swboyd@...omium.org>

This does not need a fixes tag?

/Jarkko