On 9 Jun 2001, Linus Torvalds wrote:

> The big kernel lock rules are that it's a "normal spinlock" in many
> regards, BUT you can block while holding it, and the BKL will magically
> be released during the blocking.  This means, for example, that the BKL
> can never deadlock with a semaphore - if a BKL holder blocks on sombody
> elses semaphore (and that somebody else wants the BKL), then the act of
> blocking on the semaphore will release the BKL, and allow the original
> semaphore holder to continue. 

Another difference from spinlocks is that BKL is recursive. I'm
actually surprised that it didn't show up first.

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