linux-kernel - Re: [PATCH] tty: hold lock across tty buffer finding and buffer filling

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

On Thu, 15 Mar 2012 10:14:07 +0000
"Du, Alek" <alek.du@...el.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
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