linux-kernel - Re: BUG: mmapfile/writev spurious zero bytes (x86

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Date:	Tue, 17 Jun 2008 14:24:39 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
cc:	Bron Gondwana <brong@...tmail.fm>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rob Mueller <robm@...tmail.fm>, Ingo Molnar <mingo@...e.hu>
Subject: Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i386,
 bisected, reproducable)

On Tue, 17 Jun 2008, Andi Kleen wrote:
> 
> If that fixes anything:
> - The caller is broken because it shouldn't pass a faulting source to copy_to_user()
> - And you broken copy_from_user error reporting which shares the same code

Andi, I'm sorry I cc'd you. You are the author of that crap, but the bug 
seems to be that you never even understood what copy_from_user() is 
supposed to do.

The whole *and*only* reason for copy_to/from_user() existing AT ALL is 
exactly the fact that the source or destination access can fault. 

I don't really see why you continually start arguing about things that are 
OBVIOUSLY BUGGY, as if they weren't buggy. Once somebody has debugged a 
buggy routine, you shouldn't argue against it. 

So here's a hint: next time I claim some code of yours is buggy, either 
just acknowledge the bug, or stay silent. You'll look smarter that way.

			Linus
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