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

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Message-ID: <48582E03.1040404@firstfloor.org>
Date:	Tue, 17 Jun 2008 23:34:59 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Linus Torvalds <torvalds@...ux-foundation.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)

Linus Torvalds wrote:
> 
> On Tue, 17 Jun 2008, Andi Kleen wrote:
>> Loads are not supposed to fault in copy_to_user(). Only stores are.
> 
> Andi, just shut up already.
> 
> It is "copy_user". Notice the lack of "from" or "to". That code handles 
> *both* copy_to_user and copy_from_user.

Yes, but it assumes only one can fault at a time.

> 
>> If your patch fixes something then the main wrong thing is the caller
>> who passes a faulting source address.
> 
> Andi, SHUT THE F*CK UP. Read the code. Read the patch.

I did exactly the same patch first on your first email and then I realized
it was wrong before posting ;-)

> Sorry for ever 
> involving you. I don't want to hear your idiotic whining.

The patch is wrong because it'll break the other case (in this case
copy_from_user)

-Andi

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