Re: [GIT PULL] core kernel fixes

From: Thomas Gleixner
Date: Sun Jun 21 2009 - 15:26:32 EST


On Sun, 21 Jun 2009, Linus Torvalds wrote:
> So just doing a "make_sure_its_writable()" and using handle_fault() is the
> right thing to do. Because it's what get_user_fast() would have done too,
> except it would have gone through first the fast case, and failed, then
> the slow case, and failed the lookup there, and then the slow case would
> have done that handle_mm_fault() in the end anyway.
> In fact, since you're not actually interested in the page, you _could_
> just do
> get_user_pages(tsk, mm, uaddr, 4, 1, 0, NULL, NULL);
> where a NULL "pages" pointer already tells get_user_pages() that you're
> not interested.
> That's at least cleaner than doing a "gup_fast()" (which isn't fast), and
> then freeing the page that you weren't even interested in.

Yes, you are right. The retry fixup path is after the fault and we
should go through handle_mm_fault as long as we do not have a general
available nondestructive counterpart of get_user().

I confused myself by twisting my brain whether we can simplify or even
get rid of the whole retry business.

Sorry, I did not express myself very well - looking for more than an
hour into the futex code definitely hurts your brain. It's worse than
the drugs you suspected we're on. :)


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