slab.c use of __get_user and sparse

[Sam Ravnborg <sam@ravnborg.org>]

Hi Andi, lkml.

In slab.c around line 1450 the following code is present:

list_for_each(p, &cache_chain) {
	kmem_cache_t *pc = list_entry(p, kmem_cache_t, next);
	char tmp;
	/* This happens when the module gets unloaded and doesn't
	   destroy its slab cache and noone else reuses the vmalloc
	   area of the module. Print a warning. */
	if (__get_user(tmp,(char __user *) pc->name)) { 
		printk("SLAB: cache with size %d has lost its name\n", 
			pc->objsize); 
		continue; 

sparse emit a warning for the line with __get_user because the pointer
is not marker __user. So the above cast inserted by me made sparse shut up.

Based on the comment it is understood that suddenly this pointer points
to userspace, because the module got unloaded.
I wonder why we can rely on the same address now the module got unloaded -
we may risk this virtual address is taken over by someone else?

Andi - sent to you since you made this change loong time ago.

[mm/ is sparse clean with defconfig when this is fixed].

	Sam