kernel/cpu.c: document clear_tasks_mm_cpumask()
kernel/cpu.c: document clear_tasks_mm_cpumask()

Add more comments on clear_tasks_mm_cpumask, plus adds a runtime check:
the function is only suitable for offlined CPUs, and if called
inappropriately, the kernel should scream aloud.

[5c1e68b099950c134891f0b6e179498a8ebe9cf9@linux-foundation.org: tweak comment: s/walks up/walks/, use 80 cols]
Suggested-by: Andrew Morton <5c1e68b099950c134891f0b6e179498a8ebe9cf9@linux-foundation.org>
Suggested-by: Peter Zijlstra <645ca7d3a8d3d4f60557176cd361ea8351edc32b@chello.nl>
Signed-off-by: Anton Vorontsov <1aae5ab9541d66245293c8fc1b9880f5df073631@linaro.org>
Signed-off-by: Andrew Morton <5c1e68b099950c134891f0b6e179498a8ebe9cf9@linux-foundation.org>
Signed-off-by: Linus Torvalds <69652caca27c8b940640ad396ab71f93cacec34f@linux-foundation.org>

TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas