On Fri, Jan 18, 2019 at 11:01:45AM -0800, David Tolnay wrote:
> From: David Tolnay <dtolnay@xxxxxxxxx>
> Date: Mon, 7 Jan 2019 14:36:11 -0800
> Subject: [PATCH v2] virtio-rng: Avoid repeated init of completion
>
> The virtio-rng driver uses a completion called have_data to wait for a
> virtio read to be fulfilled by the hypervisor. The completion is reset
> before placing a buffer on the virtio queue and completed by the virtio
> callback once data has been written into the buffer.
>
> Prior to this commit, the driver called init_completion on this
> completion both during probe as well as when registering virtio buffers
> as part of a hwrng read operation. The second of these init_completion
> calls should instead be reinit_completion because the have_data
> completion has already been inited by probe. As described in
> Documentation/scheduler/completion.txt, "Calling init_completion() twice
> on the same completion object is most likely a bug".
>
> This bug was present in the initial implementation of virtio-rng in
> f7f510ec1957 ("virtio: An entropy device, as suggested by hpa"). Back
> then the have_data completion was a single static completion rather than
> a member of one of potentially multiple virtrng_info structs as
> implemented later by 08e53fbdb85c ("virtio-rng: support multiple
> virtio-rng devices"). The original driver incorrectly used
> init_completion rather than INIT_COMPLETION to reset have_data during
> read.
>
> Tested by running `head -c48 /dev/random | hexdump` within crosvm, the
> Chrome OS virtual machine monitor, and confirming that the virtio-rng
> driver successfully produces random bytes from the host.
>
> Signed-off-by: David Tolnay <dtolnay@xxxxxxxxx>
> Tested-by: David Tolnay <dtolnay@xxxxxxxxx>
> ---
> drivers/char/hw_random/virtio-rng.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
Patch applied. Thanks.
--
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
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