The patch below does not apply to the 3.16-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From f49819560f53b7f3a596a8ea2e6764dc86695b62 Mon Sep 17 00:00:00 2001
From: Amos Kong <[email protected]>
Date: Thu, 11 Sep 2014 22:21:53 +0930
Subject: [PATCH] virtio-rng: skip reading when we start to remove the device

Before we really unregister the hwrng device, reading will get stuck if
the virtio device is reset. We should return error for reading when we
start to remove the device.

Signed-off-by: Amos Kong <[email protected]>
Reviewed-by: Amit Shah <[email protected]>
Cc: [email protected]
Signed-off-by: Rusty Russell <[email protected]>

diff --git a/drivers/char/hw_random/virtio-rng.c 
b/drivers/char/hw_random/virtio-rng.c
index 849b22877196..132c9ccfdc62 100644
--- a/drivers/char/hw_random/virtio-rng.c
+++ b/drivers/char/hw_random/virtio-rng.c
@@ -36,6 +36,7 @@ struct virtrng_info {
        int index;
        bool busy;
        bool hwrng_register_done;
+       bool hwrng_removed;
 };
 
 
@@ -68,6 +69,9 @@ static int virtio_read(struct hwrng *rng, void *buf, size_t 
size, bool wait)
        int ret;
        struct virtrng_info *vi = (struct virtrng_info *)rng->priv;
 
+       if (vi->hwrng_removed)
+               return -ENODEV;
+
        if (!vi->busy) {
                vi->busy = true;
                init_completion(&vi->have_data);
@@ -137,6 +141,7 @@ static void remove_common(struct virtio_device *vdev)
 {
        struct virtrng_info *vi = vdev->priv;
 
+       vi->hwrng_removed = true;
        vi->data_avail = 0;
        complete(&vi->have_data);
        vdev->config->reset(vdev);

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