[$] Detecting missing memory barriers with KCSAN

Writing (correct) concurrent code that uses locking to avoid raceconditions is difficult enough. When the objective is to use lockless algorithms, relying on memorybarriers instead of locks to eliminate locking overhead, the problembecomes harder still. Bugs are easy to create and hard to find in this type of code.There may be some help on the way, though, in the form of thispatch set from Marco Elver that enhances the KernelConcurrency Sanitizer (KCSAN) with the ability to detect some types of missingmemory barriers.