Re: Error in comment in sys/mutex.h

[Taylor R Campbell <campbell+netbsd-tech-kern%mumble.net@localhost>]

   Date: Thu, 12 Jan 2017 09:19:09 +0800 (PHT)
   From: Paul Goyette <paul%whooppee.com@localhost>

   Currently, there's a long comment in src/sys/sys/mutex.h which reads in 
   part:

   ...
     *
     *      MUTEX_OWNER(owner)
     *              Returns the owner of the adaptive mutex (LWP address).
     *
     *      MUTEX_OWNED(owner)
     *              Returns non-zero if an adaptive mutex is currently
     *              held by an LWP.
     *
   ...

   It seems to me that the arguments of these two macros should be (mtx) 
   rather than (owner).

   Am I misunderstanding something?  Or should I fix it?   :)

Actually, `owner' is correct.  Specifically, these pick apart the bits
of the struct kmutex::mtx_owner field.  Some of the bits make up a
pointer, either struct lwp * or struct cpu_info *, but in an aligned
pointer some bits are always zero, and those bits are used for other
purposes.  See, e.g., the definition of mutex_owned in kern_mutex.c.