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

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Message-ID: <alpine.LNX.2.01.0910122343340.19647@dyndns.pervalidus.net>
Date:	Mon, 12 Oct 2009 23:54:19 -0300 (BRST)
From:	"Frédéric L. W. Meunier" 
	<fredlwm@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	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>,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Subject: Re: [Bug #14388] keyboard under X with 2.6.31

On Mon, 12 Oct 2009, Linus Torvalds wrote:

> On Mon, 12 Oct 2009, Nix wrote:
>> On 12 Oct 2009, Justin P. Mattock uttered the following:
>>
>>> Not sure where this stands. Right now all three machines I have seem  to be having no issues with the kayboard
>>> (xserver 1.6.*) I can go and build the latest xserver(1.7) to see if I  hit something.
>> [...]
>>>> Bug-Entry    : http://bugzilla.kernel.org/show_bug.cgi?id=14388
>>>> Subject        : keyboard under X with 2.6.31
>>>> Submitter    : Frédéric L. W. Meunier <fredlwm@...il.com>
>>>> Date        : 2009-10-07 20:19 (5 days old)
>>>> First-Bad-Commit: http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=e043e42bdb66885b3ac10d27a01ccb9972e2b0a3
>>>> References    : http://marc.info/?l=linux-kernel&m=125494753228217&w=4
>>
>> I have been seeing problems precisely like those described (sometimes
>> the keyboard dies, sometimes it gets 'stuck' with a key held down, until
>> I switch TTYs, which generally means killing X as I'm not aware of an
>> easy way to switch VTs using only the mouse), since I moved to 2.6.31
>
> The particular commit that was bisected to should really not matter for X,
> except perhaps from a timing standpoint.
>
> The problem it fixed was in pty's, and X doesn't use them much if at all
> (various X _programs_ may, of course, but the symptoms don't sound like
> it's just a particular X app that has issues, but more of a generic X
> keyboard handling thing)
>
> But for non-pty's, there should be no semantic changes from that commit
> outside of some general tty timing differences by doing that
> tty_flush_to_ldisc() at new points.
>
> I could fairly easily imagine that some timing difference does expose
> another longer-standing problem in either the kernel or X itself. So the
> bisection isn't necessarily wrong, it's just not likely telling us what
> the real problem is.
>
> Of course, maybe there is some race condition in the tty_buffer.c code. We
> _used_ to not call flush_to_ldisc() except through the workqueue code, so
> races would not be seen in normal circumstances. Now that flush_to_ldisc()
> could easily get called both synchronously from tty_read()/tty_poll(),
> while also being hit from the workqueues.
>
> Alan, Ogawa-san, do either of you see some problem in tty_buffer.c,
> perhaps?

Just a note. With me, all the keyboard problems happened while I 
was under X, but doing something in a terminal running screen. 
Reverting the commit stopped the problem.