If the device is not ready to provide data the kernel will be stuck indefinitely in the init function. This is not a problem if the device is driven using a module, but if the driver is linked directly into the kernel then the kernel boot sequence hangs. This can happen with virtio-rng device with rng-egd backend with no data provider, for instance with QEMU command line parameters: ... -chardev socket,id=charrng0,host=localhost,port=2345,server,nowait \ -object rng-egd,id=objrng0,chardev=charrng0 \ -device virtio-rng-pci,rng=objrng0,id=rng0 To avoid that, we can call rng_get_data() in non blocking mode because the function already manages the case where byte_read is 0 (if the device is not already initialized). See also commit d3cc7996473a ("hwrng: fetch randomness only after device init") Signed-off-by: Laurent Vivier <lvivier@xxxxxxxxxx> --- drivers/char/hw_random/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c index 95be7228f327..3866d6b8017c 100644 --- a/drivers/char/hw_random/core.c +++ b/drivers/char/hw_random/core.c @@ -67,7 +67,7 @@ static void add_early_randomness(struct hwrng *rng) size_t size = min_t(size_t, 16, rng_buffer_size()); mutex_lock(&reading_mutex); - bytes_read = rng_get_data(rng, rng_buffer, size, 1); + bytes_read = rng_get_data(rng, rng_buffer, size, 0); mutex_unlock(&reading_mutex); if (bytes_read > 0) add_device_randomness(rng_buffer, bytes_read); -- 2.20.1