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authorDavid Tolnay <dtolnay@gmail.com>2019-01-07 14:36:11 -0800
committerHerbert Xu <herbert@gondor.apana.org.au>2019-01-25 18:41:52 +0800
commitaef027db48da56b6f25d0e54c07c8401ada6ce21 (patch)
treefbbe732ec4de66c749c1a50947dccefa2f93f741 /drivers/char/hw_random
parent1a5e02b6800b0164f9f617c2e230666939f2c7f5 (diff)
hwrng: virtio - 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@gmail.com> Tested-by: David Tolnay <dtolnay@gmail.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Diffstat (limited to 'drivers/char/hw_random')
-rw-r--r--drivers/char/hw_random/virtio-rng.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
index b89df66ea1ae..7abd604e938c 100644
--- a/drivers/char/hw_random/virtio-rng.c
+++ b/drivers/char/hw_random/virtio-rng.c
@@ -73,7 +73,7 @@ static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
if (!vi->busy) {
vi->busy = true;
- init_completion(&vi->have_data);
+ reinit_completion(&vi->have_data);
register_buffer(vi, buf, size);
}