Date: Fri, 7 Jan 2005 16:15:28 -0800 (PST)
From: Linus Torvalds <torvalds@osdl.org>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
cc: Marcelo Tosatti <marcelo.tosatti@cyclades.com>,
       Lukasz Trabinski <lukasz@wsisiz.edu.pl>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: uselib()  & 2.6.X?
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On Fri, 7 Jan 2005, Alan Cox wrote:
>
> Please don't use that for mainline - do_brk_locked doesn't follow kernel
> convention

I agree, I also find the "do_brk_locked()" naming confusing. To me it 
implies that we already _are_ locked, not that we're going to lock.

On the other hand, I think Alan's patch is equally confusing: the calling 
rules for "do_brk()" and "do_mmap()" are the same, and they are "caller 
takes mmap_sem". 

So I think you _both_ broke kernel conventions.

So I'd personally much prefer to just first fix the bug minimally (by just
taking the lock in the two places that need it), and then _separately_ say
"we should warn if anybody ever calls 'do_brk()' without the lock". That's 
how we tend to verify locking in other cases, ie we have things like

	if (!spin_is_locked(&t->sighand->siglock))
		BUG();

to verify the calling conventions. Same would go for mmap_sem (although we
don't seem to have any "sem_is_writelocked()" test - although you can fake
it with

	if (down_read_trylock(&mm->mmap_sem))
		BUG();

instead.

Now _that_ is a non-silent failure mode. The machine doesn't just silently 
deadlock: it tells you exactly what's wrong.

		Linus
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