linux-kernel - Re: Regression in 2.6.30 - /dev/pts - mount options

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Date:	Wed, 13 May 2009 15:03:02 +0200 (CEST)
From:	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
To:	Marc Dionne <marc.c.dionne@...il.com>
cc:	Linux Kernel Development <linux-kernel@...r.kernel.org>,
	sukadev@...ux.vnet.ibm.com, "Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Regression in 2.6.30 - /dev/pts - mount options - bisected

On Fri, 8 May 2009, Marc Dionne wrote:
> I ran into a regression from 2.6.29 to 2.6.30 on a newly installed
> fedora 11 machine.  The symptom is that things that require /dev/pts
> (gnome-terminal, konsole, xterm, etc.) don't work for a regular user,
> but run fine as root.  Everything is fine with the fedora 2.6.29
> kernel or with a self-compiled 2.6.29, but fail with a recent
> 2.6.30-rc.

When investigating a different issue on Fedora 11 on PS3, I ran into the same
problem with a 2.6.30-rc4 Fedora kernel, and with plain 2.6.30-rc4 kernels
built using a config based on the Fedora config.

> Bisection pinpoints this commit:
> http://git.kernel.org/linus/1bd7903560f1f713e85188a5aaf4d2428b6c8b50
> as the culprit, although I think that's a bit misleading.

I didn't go a far as bisecting, but strace did show it failed on opening
/dev/pts/something.

> Note that I have CONFIG_DEVPTS_MULTIPLE_INSTANCES=y.  It may be that
> user space is doing something unusual, but it passes the test of
> "works with 2.6.29, fails with 2.6.30".

Yes, it works fine with 2.6.29, so it's a regression.

> I wasn't able to reproduce on an other system with a similar configuration.

Originally, I couldn't reproduce the problem with kernels built using my
default config, which has CONFIG_DEVPTS_MULTIPLE_INSTANCES=n.

And indeed, disabling CONFIG_DEVPTS_MULTIPLE_INSTANCES in the Fedora-based
config makes the problem go away, and brings back my terminal-emulators.

With kind regards,

Geert Uytterhoeven
Software Architect
Techsoft Centre

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