Nice read, but still some misconceptions and misunderstandings. If I am in a multiprocessor design, where each processor runs completely independent from each

Nice read, but still some misconceptions and misunderstandings. If I am in a multiprocessor design, where each processor runs completely independent from each other and there is no central organizational unit like a central OS, like in many embedded designs, there is no such thing as a spinlock. A semaphore is also not used for sending processes to sleep. Linus explanation makes sense, speaking only about a single OS, which may is comprised of multiple processors. But makes no sense at all for real multi-processor designs. I don't blame him for his narrow view, more his professors that he never experienced real embedded design. I have worked in the past with multi-processors designs, where one processor was using one OS, like OS9, and the other processor had no OS at all running. Both processors where exchanging data via a dual ported RAM. So basically both processes where competing for the same resource. But even than, using a semaphore does not prevent race-conditions. Even then it is very tricky to use them. Because dual ported RAM allowed real concurrent access to the same resource. In summary, the semaphore definition is the more broad definition where 2 (or more) processes are competing for a single resource. The naming convention within Linux is more specific for this requirements. The "invented" spinlock is just a renamed version for a fast semaphore, AFAIK. Even a mutex is just a special case of a semaphore.