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

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Message-ID: <87od5zwzh2.fsf@basil.nowhere.org>
Date:	Tue, 17 Jun 2008 22:58:17 +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 <torvalds@...ux-foundation.org> writes:

>
> So I'm starting to think the bug is all in there, not in the VM itself. 
> See arch/x86/lib/copy_user_nocache.S.

The x86-64 copy_*_user functions were always designed to return errors
both ways (as in both for load and for store). That's needed because
the loops are shared for copy_to_user and copy_from_user. That's normally
ok because when you do _to_user you shouldn't fault on the loads
and vice versa. If a caller does that it's buggy.

-Andi
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