Date: Tue, 13 Oct 2009 08:02:35 -0700 (PDT)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
cc: Nix <nix@esperi.org.uk>, Paul Fulghum <paulkf@microgate.com>,
       "Justin P. Mattock" <justinmattock@gmail.com>,
       "Rafael J. Wysocki" <rjw@sisk.pl>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Kernel Testers List <kernel-testers@vger.kernel.org>,
       Boyan <btanastasov@yahoo.co.uk>,
       Dmitry Torokhov <dmitry.torokhov@gmail.com>, Ed Tomlinson <edt@aei.ca>,
       =?ISO-8859-15?Q?Fr=E9d=E9ric_L=2E_W=2E_Meunier?= 
	<fredlwm@gmail.com>,
       OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Subject: Re: [Bug #14388] keyboard under X with 2.6.31
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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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