[PATCH] riscv: Fix a NULL pointer reference in machine_kexec_prepare

[Markus Elfring]

> A NULL pointer reference issue is noticed in riscv's machine_kexec_prepare,
…
                 dereference?


…
> Fix this by simply adding a check before copy.

How do you think about to add any tags (like “Fixes” and “Cc”) accordingly?

See also:
* https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?h=v7.2-rc1#n145
* https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/stable-kernel-rules.rst?h=v7.2-rc1#n34


Regards,
Markus