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From: "Maciej S. Szmigiero" <mail@maciej.szmigiero.name>
To: Stephen Boyd <swboyd@chromium.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>,
	linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org,
	Andrey Pronin <apronin@chromium.org>,
	Duncan Laurie <dlaurie@chromium.org>,
	Jason Gunthorpe <jgg@ziepe.ca>, Arnd Bergmann <arnd@arndb.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Guenter Roeck <groeck@chromium.org>,
	Alexander Steffen <Alexander.Steffen@infineon.com>
Subject: Re: [PATCH v3] hwrng: core: Freeze khwrng thread during suspend
Date: Tue, 29 Oct 2019 00:45:31 +0100
Message-ID: <4a45b3e0-ed3a-61d3-bfc6-957c7ba631bb@maciej.szmigiero.name> (raw)
In-Reply-To: <20190805233241.220521-1-swboyd@chromium.org>

Hi Stephen,

On 06.08.2019 01:32, 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.

This patch broke suspend with virtio-rng loaded (it hangs).

The problematic call chain is:
virtrng_freeze() -> remove_common() -> hwrng_unregister() ->
kthread_stop().

It looks like kthread_stop() can't finish on a frozen khwrng thread.

Reverting this commit makes a VM with virtio-rng driver loaded
suspend and resume correctly again.

Maciej

  parent reply index

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-05 23:32 Stephen Boyd
2019-08-06 15:01 ` Stephen Boyd
2019-08-15 12:06 ` Herbert Xu
2019-10-28 23:45 ` Maciej S. Szmigiero [this message]
     [not found]   ` <5db85058.1c69fb81.202d7.e3d0@mx.google.com>
2019-10-29 15:50     ` Maciej S. Szmigiero
     [not found]       ` <5dc0c12e.1c69fb81.2ce1c.01ee@mx.google.com>
2019-11-10  0:30         ` Maciej S. Szmigiero

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