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

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Message-ID: <4858295D.8000904@firstfloor.org>
Date:	Tue, 17 Jun 2008 23:15:09 +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, Linus Torvalds wrote:
>> I actually am starting to think that the bug is in 
>> __copy_to_user_inatomic_nocache().
> 
> Confirmed.
> 
> The uncached user copies are totally broken. The number of bytes left 
> uncopied is simply wrong, because of how it does that unrolled loop and 
> doesn't account for the fact that just doing loads does not actually 
> increase the number of bytes copied at all.

How can a load fault legitimately in copy_to_user?

-Andi


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