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

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Date:	Fri, 16 Mar 2012 11:22:01 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	"Du, Alek" <alek.du@...el.com>
CC:	Jiri Slaby <jirislaby@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"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 03/16/2012 11:08 AM, Du, Alek wrote:
> If you really look at the original patch from Xiaobing, the tty_prepare_flip_string is also patched :-)
> Actually it fills up all the possible spin_lock gaps in tty_buffer.c
> 
> 
> @@ -344,13 +375,20 @@ EXPORT_SYMBOL(tty_schedule_flip);  int tty_prepare_flip_string(struct tty_struct *tty, unsigned char **chars,
>  								size_t size)
>  {
> -	int space = tty_buffer_request_room(tty, size);
> +	int space;
> +	unsigned long flags;
> +	struct tty_buffer *tb;
> +	
> +	spin_lock_irqsave(&tty->buf.lock, flags);
> +	space = __tty_buffer_request_room(tty, size);
> +
> +	tb = tty->buf.tail;
>  	if (likely(space)) {
> -		struct tty_buffer *tb = tty->buf.tail;
>  		*chars = tb->char_buf_ptr + tb->used;
                ^^^^^^
This is returned to the caller. And it writes to that. And it may be
gone as soon as the lock is unlocked below.

>  		memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
>  		tb->used += space;
>  	}
> +	spin_unlock_irqrestore(&tty->buf.lock, flags);
>  	return space;
>  }

thanks,
-- 
js
suse labs
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