Bug report: cpu_relax call from vdso space

[Denis Ivanov]

Hello,

Segmentation fault may be raised from cpu_relax() 
(arch/riscv/include/asm/vdso/processor.h).

cpu_relax() may be called from vDSO functions (ex: 
__vdso_clock_gettime). This means that global 'riscv_isa_ext_keys' 
variable must not be used in cpu_relax() directly.

Use of this array was added to cpu_relax() in
https://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux.git/commit/?h=fixes&id=8eb060e10185cfc97ef0200d197ec246ba0f9f8c

Denis Ivanov