hwrng: virtio - don't wait on cleanup

[ Upstream commit 2bb31abdbe55742c89f4dc0cc26fcbc8467364f6 ]

When virtio-rng device was dropped by the hwrng core we were forced
to wait the buffer to come back from the device to not have
remaining ongoing operation that could spoil the buffer.

But now, as the buffer is internal to the virtio-rng we can release
the waiting loop immediately, the buffer will be retrieve and use
when the virtio-rng driver will be selected again.

This avoids to hang on an rng_current write command if the virtio-rng
device is blocked by a lack of entropy. This allows to select
another entropy source if the current one is empty.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Link: https://lore.kernel.org/r/20211028101111.128049-3-lvivier@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Stable-dep-of: ac52578d6e8d ("hwrng: virtio - Fix race on data_avail and actual data")
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
index 23149e94d621fbb94a40c95f20eb52754d0c555f..c8f5a3392e48c29154bbb2a078662e21aa19a55c 100644 (file)
--- a/drivers/char/hw_random/virtio-rng.c
+++ b/drivers/char/hw_random/virtio-rng.c
@@ -81,6 +81,11 @@ static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
                ret = wait_for_completion_killable(&vi->have_data);
                if (ret < 0)
                        return ret;
+               /* if vi->data_avail is 0, we have been interrupted
+                * by a cleanup, but buffer stays in the queue
+                */
+               if (vi->data_avail == 0)
+                       return read;
 
                chunk = min_t(unsigned int, size, vi->data_avail);
                memcpy(buf + read, vi->data, chunk);
@@ -104,7 +109,7 @@ static void virtio_cleanup(struct hwrng *rng)
        struct virtrng_info *vi = (struct virtrng_info *)rng->priv;
 
        if (vi->busy)
-               wait_for_completion(&vi->have_data);
+               complete(&vi->have_data);
 }
 
 static int probe_common(struct virtio_device *vdev)