linux-kernel - Re: [Bug #14388] keyboard under X with 2.6.31

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Message-ID: <alpine.LFD.2.01.0910130755360.3438@localhost.localdomain>
Date:	Tue, 13 Oct 2009 08:02:35 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
cc:	Nix <nix@...eri.org.uk>, Paul Fulghum <paulkf@...rogate.com>,
	"Justin P. Mattock" <justinmattock@...il.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Boyan <btanastasov@...oo.co.uk>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Ed Tomlinson <edt@....ca>,
	Frédéric L. W. Meunier 
	<fredlwm@...il.com>, OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Subject: Re: [Bug #14388] keyboard under X with 2.6.31



On Tue, 13 Oct 2009, Linus Torvalds wrote:
> 
>  - whoever is _reading_ the buffer, and due to memory ordering may see the 
>    update to the buffer length _before_ it actually sees the data itself. 
>    That spinlock does all the memory ordering too.

Hmm. This one looks like it's ok, because whenever we commit it, we do 
take the spinlock, so '->commit' is protected for the reader side.

>  - scrambling the data order with two writers is certainly less annoying 
>    than potentially screwing up ->used entirely, and having the memcpy's 
>    overflow the buffer. Both writers may have decided that there is enough 
>    room for each one - but that does not mean that there is enough room 
>    for _both_.

.. but this one is still true. Anybody who doesn't lock writers at a 
higher level could easily end up causing some really subtle memory 
corruption.

But maybe all users really are safe. 

		Linus
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