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

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Message-ID: <20190717113956.GA12119@ziepe.ca>
Date:   Wed, 17 Jul 2019 08:39:56 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Peter Huewe <peterhuewe@....de>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, 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.

You mean the TPM here right?

Should we be more careful in the TPM code to check if the TPM is
suspended before trying to use it, rather than muck up callers?

Jason