linux-kernel - Re: [PATCH] hw_random: don't wait on add_early

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Message-ID: <20190920130319.GA23697@gondor.apana.org.au>
Date:   Fri, 20 Sep 2019 23:03:20 +1000
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Laurent Vivier <lvivier@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Amit Shah <amit@...nel.org>,
        linux-crypto@...r.kernel.org, Matt Mackall <mpm@...enic.com>
Subject: Re: [PATCH] hw_random: don't wait on add_early_randomness()

On Tue, Sep 17, 2019 at 03:02:26PM +0200, Laurent Vivier wrote:
> On 17/09/2019 14:40, Herbert Xu wrote:
> > On Tue, Sep 17, 2019 at 11:54:50AM +0200, Laurent Vivier wrote:
> >> add_early_randomness() is called by hwrng_register() when the
> >> hardware is added. If this hardware and its module are present
> >> at boot, and if there is no data available the boot hangs until
> >> data are available and can't be interrupted.
> >>
> >> To avoid that, call rng_get_data() in non-blocking mode (wait=0)
> >> from add_early_randomness().
> >>
> >> Signed-off-by: Laurent Vivier <lvivier@...hat.com>
> >> ---
> >>  drivers/char/hw_random/core.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > Please provide more context in your patch description such as which
> > driver actually causes a hang here.
> 
> I can add in the next version:
> 
> "For instance, in the case of virtio-rng, in some cases the host can be
> not able to provide enough entropy for all the guests.
> 
> We can have two easy ways to reproduce the problem but they rely on
> misconfiguration of the hypervisor or the egd daemon:
> 
> - if virtio-rng device is configured to connect to the egd daemon of the
> host but when the virtio-rng driver asks for data the daemon is not
> connected,
> 
> - if virtio-rng device is configured to connect to the egd daemon of the
> host but the egd daemon doesn't provide data.
> 
> The guest kernel will hang at boot until the virtio-rng driver provides
> enough data."

Patch applied with this addition.  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