Re: [PATCH 16/16] mm/sl[au]b: check if large object is valid in __ksize()

[Christoph Lameter]

On Wed, 13 Jul 2022, Hyeonggon Yoo wrote:

> > Why return 0 if there is an error and why bother the callers with these
> > checks. BUG()?
>
> I thought BUG should be used when there is no other solution.

Spurios returns of 0 that the caller has to check for is a solution?

> > I guess this is an error since the order-0 page cannot come from slab
> > allocations.
>
> comment in ksize() says:
> 	"The caller must guarantee that objp points to a valid object
> 	previously allocated with either kmalloc() or kmem_cache_alloc()."
>
> It should not be used on order-0 page that is not allocated from slab. No?

I guess we would need to check. Code could exist that does this.

Getting a 0 size would be surprising too here. BUG()? Or WARN() and return
PAGE_SIZE.