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
