locking-debug-2021-09-01

 - Update documentation and code example

KCSAN updates:

 - Introduce CONFIG_KCSAN_STRICT (which RCU uses)
 - Optimize use of get_ctx() by kcsan_found_watchpoint()
 - Rework atomic.h into permissive.h
 - Add the ability to ignore writes that change only one bit of a given data-racy variable.
 - Improve comments

Signed-off-by: Ingo Molnar <mingo@kernel.org>