Re: [CHECKER] repetitive/contradictory comparison bugs for 2.4.7

[Alan Cox]

> other 10 are questionable.  Those 10 are all simple variations on the
> following code:
> 
> Start --->
> 	if (!tmp_buf) {
> 		page = get_free_page(GFP_KERNEL);
> 
> Error --->
> 		if (tmp_buf)
> 			free_page(page);
> 		else
> 			tmp_buf = (unsigned char *) page;
> 	}

That one is not a bug. The serial drivers do this to handle a race. Really
it should be

		page = get_free_page(GFP_KERNEL)

		rmb();
		if (tmp_buf)
			..

but this will go away as and when someone switches the tty layer to new 
style locking. The precise code flow (under lock_kernel in both cases) is

	
	if (!tmp_buf)
	{
		/* tmp_buf was 0
		page = get_free_page (...)
		[SLEEPS, TASK SWITCH]

		if(tmp_buf)
		/* tmp buf was non zero - another thread allocated it */

Alan