On 2/10/22 11:17, Minchan Kim wrote:
* pin_user_pages() - pin user pages in memory for use by other devices
< snip >
* @pages: array that receives pointers to the pages pinned.
* Should be at least nr_pages long. Or NULL, if caller
* only intends to ensure the pages are faulted in.
pin_user_pages(,, pages = NULL, );
gup_flags |= FOLL_PIN
__get_user_pages_locked
__get_user_pages
..
VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
Only FOLL_GET or FOLL_PIN are supposed to fill in the **pages array. So
if a caller passes a null **pages arg, then that caller must not also
set FOLL_GET or FOLL_PIN. That's what the VM_BUG_ON() is expressing.
Perhaps that should be part of the documentation. It sort of is already,
for get_user_pages*().
thanks,
--
John Hubbard
NVIDIA
