On 13 May 2021, at 17:23, Yang Shi wrote: > 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() for try_to_unmap() and > do so for the VM_BUG_ON_PAGE in split_huge_page_to_list as well. > > This changed the semantic of try_to_unmap(), but I don't see there is > any usecase that expects try_to_unmap() just unmap one subpage of a huge > page. So using page_mapcount() seems like a bug. > > [1] https://lore.kernel.org/linux-mm/20210412180659.B9E3.409509F4@xxxxxxxxxxxx/ > > Signed-off-by: Yang Shi <shy828301@xxxxxxxxx> > --- > v2: Removed dead code and updated the comment of try_to_unmap() per Zi > Yan. > > mm/huge_memory.c | 11 +---------- > mm/rmap.c | 10 ++++++---- > 2 files changed, 7 insertions(+), 14 deletions(-) LGTM. Thanks. Reviewed-by: Zi Yan <ziy@xxxxxxxxxx> — Best Regards, Yan Zi
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