linux-kernel - Re: [BUG] tty: Userland can create hung tasks

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Message-ID: <20171101170908.6ad08580@alans-desktop>
Date:   Wed, 1 Nov 2017 17:09:08 +0000
From:   Alan Cox <alan@...yncelyn.cymru>
To:     Tejun Heo <tj@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: Re: [BUG] tty: Userland can create hung tasks

On Tue, 31 Oct 2017 19:06:51 -0700
Tejun Heo <tj@...nel.org> wrote:

> Hello,
> 
> tty hangup code doesn't mark the console as being HUPed for, e.g.,
> /dev/console and that can put the session leader trying to
> disassociate from the controlling terminal in an indefinite D sleep.
> 
> Looking at the code, I have no idea why some tty devices are never
> marked being hung up.  It *looks* intentional and dates back to the
> git origin but I couldn't find any clue.  The following patch is a
> workaround which fixes the observed problem but definitely isn't the
> proper fix.

Two reasons

1. It broke the serial consoles because they would hang up and close down
the hardware. With tty_port that *should* be fixable properly for any
cases remaining.

2. The console layer was (and still is) completely broken and doens't
refcount properly. So if you turn on console hangups it breaks (as indeed
does freeing consoles and half a dozen other things).

Sadly it seems that nobody cares about the console.

Alan