78887832e7
add_early_randomness() is called by hwrng_register() when the
hardware is added. If this hardware and its module are present
at boot, and if there is no data available the boot hangs until
data are available and can't be interrupted.
For instance, in the case of virtio-rng, in some cases the host can be
not able to provide enough entropy for all the guests.
We can have two easy ways to reproduce the problem but they rely on
misconfiguration of the hypervisor or the egd daemon:
- if virtio-rng device is configured to connect to the egd daemon of the
host but when the virtio-rng driver asks for data the daemon is not
connected,
- if virtio-rng device is configured to connect to the egd daemon of the
host but the egd daemon doesn't provide data.
The guest kernel will hang at boot until the virtio-rng driver provides
enough data.
To avoid that, call rng_get_data() in non-blocking mode (wait=0)
from add_early_randomness().
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Fixes: d9e797261933 ("hwrng: add randomness to system from rng...")
Cc: <stable@vger.kernel.org>
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.