On Fri, Mar 01, 2024 at 09:47:06PM +0000, Matthew Wilcox (Oracle) wrote: > At least two places (memory failure and page migration) need to call > folio_test_hugetlb() without a reference on the folio. This can currently > result in false positives (returning true when the folio doesn't belong > to hugetlb) and more commonly in VM_BUG_ON() when a folio is split. > > The new way to distinguish a hugetlb folio is to see if (1) the page > is compound (or the folio is large) and (2) page[1].mapping is set to > the address of hugetlb_lock. If the folio is (or has been) large then > page[1] is guaranteed to exist. If the folio is split between the two > tests, page[1].mapping will be set to something which definitely isn't > the address of hugetlb_lock. > > Because we shift around the layout of struct folio a bit, we now use > page[1].private, which means we need to adjust __split_huge_page_tail() > a little. We also need to annoy the vmcore_info people again. Sorry. > > Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Thanks for working on this Willy! I thought about whether we want a Fixes tag here, but since we are only bugging under DEBUG_VM, and the false positives/negatives can be rechecked under the lock, I guess it does not matter: Reviewed-by: Oscar Salvador <osalvador@xxxxxxx> -- Oscar Salvador SUSE Labs
