Subject: Re: In last setsid/tty locking changes...
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Marco Cipullo <cipullo@libero.it>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
In-Reply-To: <200501071437.02426.cipullo@libero.it>
References: <200501071437.02426.cipullo@libero.it>
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Date: Fri, 07 Jan 2005 15:45:42 +0000
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On Gwe, 2005-01-07 at 13:37, Marco Cipullo wrote:
> In last setsid/tty locking changes:
> +	down(&tty_sem);
>  	current->signal->tty = NULL;
> +	up(&tty_sem);
>  
>  	/* Block and flush all signals */
>  	sigfillset(&blocked);
> 
> Sorry for the silly question, but why is needed a semaphore to write just one 
> value without read/write nothing else?

Look at the tty init_dev code paths and it might make more sense. It
doesn't just say "protect this write" more importantly it says "don't do
this in parallel with tty setup"

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