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David Tolnay
aef027db48
The virtio-rng driver uses a completion called have_data to wait for a virtio read to be fulfilled by the hypervisor. The completion is reset before placing a buffer on the virtio queue and completed by the virtio callback once data has been written into the buffer. Prior to this commit, the driver called init_completion on this completion both during probe as well as when registering virtio buffers as part of a hwrng read operation. The second of these init_completion calls should instead be reinit_completion because the have_data completion has already been inited by probe. As described in Documentation/scheduler/completion.txt, "Calling init_completion() twice on the same completion object is most likely a bug". This bug was present in the initial implementation of virtio-rng inf7f510ec19("virtio: An entropy device, as suggested by hpa"). Back then the have_data completion was a single static completion rather than a member of one of potentially multiple virtrng_info structs as implemented later by08e53fbdb8("virtio-rng: support multiple virtio-rng devices"). The original driver incorrectly used init_completion rather than INIT_COMPLETION to reset have_data during read. Tested by running `head -c48 /dev/random | hexdump` within crosvm, the Chrome OS virtual machine monitor, and confirming that the virtio-rng driver successfully produces random bytes from the host. Signed-off-by: David Tolnay <dtolnay@gmail.com> Tested-by: David Tolnay <dtolnay@gmail.com> 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.