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Date: Thu, 15 Mar 2012 15:40:18 +0000
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: "Du, Alek" <alek.du@intel.com>
Cc: "Tu, Xiaobing" <xiaobing.tu@intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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        "Zhang, Yanmin" <yanmin.zhang@intel.com>,
        "Zuo, Jiao" <jiao.zuo@intel.com>
Subject: Re: [PATCH] tty: hold lock across tty buffer finding and buffer
 filling
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On Thu, 15 Mar 2012 10:14:07 +0000
"Du, Alek" <alek.du@intel.com> wrote:

> Alan,
> 
> I agree with you for the case of multiple writers to the tty buffer.
> 
> But there is another case that cause kernel hang: driver is writing data to tty, while app shutdown the port or flush through IOCTL. The buf.tail is set to NULL, here is the log:
> 
> 
> <1>[ 4713.451954] BUG: unable to handle kernel NULL pointer dereference at
> 00000004
> <1>[ 4713.452424] IP: [<c14ff59c>] tty_insert_flip_string_fixed_flag+0x4c/0x90


Ouch.. yes that makes sense.

Alan