linux-kernel - Re: [PATCH] tty: Fix race condition between __tty_buffer_request_room and flush_to

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Date:	Fri, 18 Apr 2014 10:10:17 +0200
From:	Manfred Schlaegl <manfred.schlaegl@....at>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Peter Hurley <peter@...leysoftware.com>,
	Alan Cox <alan@...hat.com>, linux-kernel@...r.kernel.org,
	Manfred Schlaegl <manfred.schlaegl@...zinger.com>
Subject: Re: [PATCH] tty: Fix race condition between __tty_buffer_request_room
 and flush_to_ldisc

On 2014-04-08 14:42, Manfred Schlaegl wrote:
> The race was introduced while development of linux-3.11 by
> e8437d7ecbc50198705331449367d401ebb3181f and
> e9975fdec0138f1b2a85b9624e41660abd9865d4.
> Originally it was found and reproduced on linux-3.12.15 and
> linux-3.12.15-rt25, by sending 500 byte blocks with 115kbaud to the
> target uart in a loop with 100 milliseconds delay.
> 
> In short:
>  1. The consumer flush_to_ldisc is on to remove the head tty_buffer.
>  2. The producer adds a number of bytes, so that a new tty_buffer must
> 	be allocated and added by __tty_buffer_request_room.
>  3. The consumer removes the head tty_buffer element, without handling
> 	newly committed data.

Hi!

Reminder: The Problem is still existent in linux-3.11, 3.12, 3.13. 3.14 and pre 3.15 kernels.

The lastly delivered patch cleanly applies to pre 3.15 (torvalds tree) and 3.14(.1).

Manfred
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