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

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Message-Id: <1255446531.3423.8.camel@x2.microgate.com>
Date:	Tue, 13 Oct 2009 10:08:51 -0500
From:	Paul Fulghum <paulkf@...rogate.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, Nix <nix@...eri.org.uk>,
	"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, 2009-10-13 at 07:39 -0700, Linus Torvalds wrote:

> You also can race with:
> 
>  - 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.

The only reader is flush_to_ldisc() which operates on the
'commit' and 'read' fields of the buffer.

tty_prepare_xxx and tty_insert_xxx operate on the 'used'
field of the buffer

'commit' is updated with 'used' only under spinlock when
tty_flip_buffer_push() is called after the producer is
finished filling a buffer or in tty_buffer_request_room()
when allocating a new buffer.

--
Paul Fulghum
Microgate Systems, Ltd

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