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

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Message-ID: <485838F9.8010001@firstfloor.org>
Date:	Wed, 18 Jun 2008 00:21:45 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Al Viro <viro@...IV.linux.org.uk>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	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)


> AFAICS, what happened is that b0rken copy_*FROM*_user() had been discussed
> with references to copy_*TO*_user().  With proposed patch indeed not affecting
> any legitimate calls of the latter.  Does affect the former and that, from
> my reading of the code in question, correctly.
> 
> IOW, s/copy_to_user/copy_from_user/ in Linus' postings upthread and they
> make sense.

Yes, it makes some more sense, but I'm not completely happy with the fix
because it makes the fault point reporting very unreliable (maximum error
will be 63 instead of 7 now). iirc especially mount was sensitive to that.

Unfortunately fixing the accuracy is a little tricky.

-Andi
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