For MADV_DONTNEED to work properly with huge pages, it's critical to not clear pmd intermittently unless you hold down_write(mmap_sem). Otherwise MADV_DONTNEED can miss the THP which can lead to userspace breakage.
See example of such race in commit message of patch 2/4. All these races are found by code inspection. I haven't seen them triggered. I don't think it's worth to apply them to stable@. Kirill A. Shutemov (4): thp: reduce indentation level in change_huge_pmd() thp: fix MADV_DONTNEED vs. numa balancing race thp: fix MADV_DONTNEED vs. MADV_FREE race thp: fix MADV_DONTNEED vs clear soft dirty race fs/proc/task_mmu.c | 9 +++++- mm/huge_memory.c | 86 ++++++++++++++++++++++++++++++++++++------------------ 2 files changed, 66 insertions(+), 29 deletions(-) -- 2.11.0
