linux-kernel - Re: [PATCH 0/2] drivers:tty:pty: Fix a race causing data loss on close

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Message-ID: <X/cplo+nw5IaG3CJ@kroah.com>
Date:   Thu, 7 Jan 2021 16:32:38 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     minyard@....org
Cc:     Jiri Slaby <jirislaby@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Hurley <peter@...leysoftware.com>,
        brian.bloniarz@...il.com
Subject: Re: [PATCH 0/2] drivers:tty:pty: Fix a race causing data loss on
 close

On Mon, Nov 23, 2020 at 06:49:00PM -0600, minyard@....org wrote:
> I finally got some time to spend with this issue, and I think I have a
> good fix.  Not really a v2, this is a completely different fix.
> Basically, calling tty_vhangup() on the slave when closing a pty master
> is just a bad idea.
> 
> >From what I can tell, the tty_vhangup() is there in case there was a
> console redirect to the pty slave.  When you close the master, you need
> to release the redirect.  I didn't see another reason for tty_vhangup().
> So this has two parts, export the release of the tty redirect release
> for the pty code to use, and call it from the pty code.
> 
> With this change, everything seems to work ok and no data is lost on the
> slave side if the master closes with outstanding data.  I have updated
> my test program to check that all written data is read, it's available
> at https://sourceforge.net/projects/ser2net/files/tmp/testpty.c/download
> 
> But, this code is quite intricate and I certainly may have missed
> something.

Tricky stuff, but I think this makes sense, so let's see how the
test-builders and linux-next work with this...

thanks,

greg k-h