linux-kernel - TIOCGWINSZ retuns old pty size after receiving SIGWINCH

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Message-ID: <20080810150859.GO3653@pruts.nl>
Date:	Sun, 10 Aug 2008 17:08:59 +0200
From:	Ico Doornekamp <lkml@...v.nl>
To:	linux-kernel@...r.kernel.org
Subject: TIOCGWINSZ retuns old pty size after receiving SIGWINCH

Hello,

Recently my X terminals showed annoying behaviour where the application
in the terminal was not resized properly to the actual size of the X
terminal emulator window, resulting in a lot of misaligned text on the
screen. Hunting the issue down from the windowmanager and the terminal
emulator program, I suspect the problem might lie in the kernel. I'm
running 2.6.26 on a dual core i386.

What I see is this: the userspace application receives a SIGWINCH signal
and acquires the terminal size usign the TIOCGWINSZ ioctl. It seems that
in some cases the old instead of the new terminal size is returned.
A small delay before the ioctl seems to 'fix' this behaviour.

I noticed some changes involving locking in the the pty code in the last
kernel verions, could one of these changes cause the above behaviour ? If
so, wouldn't this affect much more users ?

Ico

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