linux-kernel - Re: [PATCH 0/2] SIGWINCH problem with terminal apps still alive

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Date:	Sun, 12 Oct 2008 19:03:12 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Adam Tlałka <atlka@...gda.pl>
Cc:	7eggert@....de, linux-kernel@...r.kernel.org, torvalds@...l.org
Subject: Re: [PATCH 0/2] SIGWINCH problem with terminal apps still alive

> I've read the code. The race problem with xterm or other pty using

Clearly not.

> program in 2.6.26 appeared because one app called ioctl(TIOCSWINSZ) on
> the master side while other read winsize (TIOCGWINSZ) using client side
> (slave). So in one ioctl() call tty == master and in other tty ==
> real_tty. Of course we can have the opposite situaction so terminal app

Then we end up with both using real_tty.

> Anyway I think that you miss the point. Why using
> real_tty->termios_mutex instead of tty->termios_mutex in tty_do_resize

To avoid deadlocks if you took both as you updated both structures.

> So it seems that tty->termios_mutex could point to different
> location in different calls but real_tty->termios_mutex always points
> to the same location.

You've finally got there - we always work off real_tty. That is why we
can safely use the mutex on the real_tty side.

Alan
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