linux-kernel - Re: [PATCH] tty/tty_io.c: make a check before reuse cdev

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Date:	Mon, 21 Jul 2014 08:38:40 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	pp <mnipxh@...il.com>
Cc:	jslaby@...e.cz, linux-kernel@...r.kernel.org,
	yanmin_zhang@...ux.intel.com, xinhuix.pan@...el.com
Subject: Re: [PATCH] tty/tty_io.c: make a check before reuse cdev

On Mon, Jul 21, 2014 at 08:47:16PM +0800, pp wrote:
> As reuse the cdev may cause panic. After we unregister the tty device, we may use tty_hangup() o
> other similar function to send a signal(SIGHUP) to process which has opend our device. But that
> not succeed if the process couldn't get the signal. for example, a process forked
> but his parent quited never get SIGHUP.
> 
> Here is our scence.
> tty driver register its device and init the cdevs, then process "A" open one cdev.
> tty driver unregister its device and cdev_del the cdevs, call tty_hangup to (S)send signal SIGHUP to process A.
> But that step(S) fails.

How can that fail?  What driver does this fail for?

> tty driver register its device and (D)init the cdevs again.

What driver does this with an "old" device, it should have created a new
one, otherwise, as you have pointed out, it's a bug.

thanks,

greg k-h
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