Re: Error in comment in sys/mutex.h

[Paul Goyette <paul%whooppee.com@localhost>]

On Thu, 12 Jan 2017, Taylor R Campbell wrote:

>   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.

Ah, OK, got it!  Thanks!


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