linux-kernel - Re: [PATCH v3] hwrng: core: Freeze khwrng thread during suspend

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Message-ID: <5d49962d.1c69fb81.6e0a5.148a@mx.google.com>
Date:   Tue, 06 Aug 2019 08:01:00 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        Andrey Pronin <apronin@...omium.org>,
        Duncan Laurie <dlaurie@...omium.org>,
        Jason Gunthorpe <jgg@...pe.ca>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Guenter Roeck <groeck@...omium.org>,
        Alexander Steffen <Alexander.Steffen@...ineon.com>
Subject: Re: [PATCH v3] hwrng: core: Freeze khwrng thread during suspend

Quoting Stephen Boyd (2019-08-05 16:32:41)
> 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: Duncan Laurie <dlaurie@...omium.org>
> Cc: Jason Gunthorpe <jgg@...pe.ca>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Guenter Roeck <groeck@...omium.org>
> Cc: Alexander Steffen <Alexander.Steffen@...ineon.com>
> Signed-off-by: Stephen Boyd <swboyd@...omium.org>
> ---

Sorry, forgot to add

Fixes: be4000bc4644 ("hwrng: create filler thread")