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

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Message-ID: <20190815120607.GB29355@gondor.apana.org.au>
Date:   Thu, 15 Aug 2019 22:06:07 +1000
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Stephen Boyd <swboyd@...omium.org>
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

On Mon, Aug 05, 2019 at 04:32:41PM -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: 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>
> ---
> 
> I'm splitting this patch off of the larger series so it can
> go through the crypto tree. See [1] for the prevoius round.
> Nothing has changed in this patch since then.
> 
> [1] https://lkml.kernel.org/r/20190716224518.62556-2-swboyd@chromium.org
> 
>  drivers/char/hw_random/core.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)

Patch applied.  Thanks.
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt