slab: Mark large folios for debugging purposes

slab: Mark large folios for debugging purposes

If a user calls p = kmalloc(1024); kfree(p); kfree(p); and 'p' was the
only object in the slab, we may free the slab after the first call to
kfree().  If we do, we clear PGTY_slab and the second call to kfree()
will call free_large_kmalloc().  That will leave a trace in the logs
("object pointer: 0x%p"), but otherwise proceed to free the memory,
which is likely to corrupt the page allocator's metadata.

Allocate a new page type for large kmalloc and mark the memory with it
while it's allocated.  That lets us detect this double-free and return
without harming any data structures.

Reported-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>