When debugging the bug reported by Wang Yugui [1], try_to_unmap() may return false positive for PTE-mapped THP since page_mapcount() is used to check if the THP is unmapped, but it just checks compound mapount and head page's mapcount. If the THP is PTE-mapped and head page is not mapped, it may return false positive. Use total_mapcount() instead of page_mapcount() and do so for the VM_BUG_ON_PAGE in split_huge_page_to_list as well. [1] https://lore.kernel.org/linux-mm/20210412180659.B9E3.409509F4@xxxxxxxxxxxx/ Signed-off-by: Yang Shi <shy828301@xxxxxxxxx> --- mm/huge_memory.c | 2 +- mm/rmap.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 63ed6b25deaa..2122c3e853b9 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2718,7 +2718,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) } unmap_page(head); - VM_BUG_ON_PAGE(compound_mapcount(head), head); + VM_BUG_ON_PAGE(total_mapcount(head), head); /* block interrupt reentry in xa_lock and spinlock */ local_irq_disable(); diff --git a/mm/rmap.c b/mm/rmap.c index 693a610e181d..2e547378ab5f 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1777,7 +1777,7 @@ bool try_to_unmap(struct page *page, enum ttu_flags flags) else rmap_walk(page, &rwc); - return !page_mapcount(page) ? true : false; + return !total_mapcount(page) ? true : false; } /** -- 2.26.2
