Re: [PATCH] Alternate futex non-page-pinning and COW fix

[Jamie Lokier]

Linus Torvalds wrote:
> >     * A futex on a MAP_PRIVATE must be mm-local: the canonical
> >     * example being MAP_PRIVATE of /dev/zero.
> 
> Actually, /dev/zero is a special case in itself. It is an anonymous 
> mapping, and is equivalent to MAP_ANON for private mappings. For 
> MAP_SHARED it is something _totally_ different.

Well yes, but conceptually it's behaviour is that of a private mapping
of a file-like object.  But fine, let's not get sidetracked by /dev/zero.

I'll restate it:

	* A futex on a MAP_PRIVATE must be mm-local.  The canonical
	example being the data section of your executable.

> > Unfortunately I think the above 5 conditions do not have a consistent
> > solution.  Please prove me wrong :)
> 
> I don't think there is any inconsistency.

I can't think of a behaviour which satisfies all 5 conditions, so
you'll have to help me out. :/

-- Jamie

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