linux-kernel - Re: [PATCH] tty: Correct tty buffer flush.

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Message-ID: <20121204141223.2ecb0f76@pyramind.ukuu.org.uk>
Date:	Tue, 4 Dec 2012 14:12:23 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Ilya Zykov <ilya@...x.ru>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alan Cox <alan@...ux.intel.com>, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org
Subject: Re: [PATCH] tty: Correct tty buffer flush.

On Tue, 04 Dec 2012 17:10:57 +0400
Ilya Zykov <ilya@...x.ru> wrote:

>   The root of problem is carelessly zeroing pointer(in function __tty_buffer_flush()),
> when another thread can use it. It can be cause of "NULL pointer dereference".
>   Main idea of the patch, this is never free last (struct tty_buffer) in the active buffer.
> Only flush the data for ldisc(tty->buf.head->read = tty->buf.head->commit).
> At that moment driver can collect(write) data in buffer without conflict.
> It is repeat behavior of flush_to_ldisc(), only without feeding data to ldisc.
> 
> Also revert:
>   commit c56a00a165712fd73081f40044b1e64407bb1875
>   tty: hold lock across tty buffer finding and buffer filling
> In order to delete the unneeded locks any more.
> 
> Signed-off-by: Ilya Zykov <ilya@...x.ru>

Acked-by: Alan Cox <alan@...ux.intel.com>
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