From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> Subject: thp: reduce indentation level in change_huge_pmd() Patch series "thp: fix few MADV_DONTNEED races" 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@. This patch (of 4): Restructure code in preparation for a fix. Link: http://lkml.kernel.org/r/20170302151034.27829-2-kirill.shutemov@xxxxxxxxxxxxxxx Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/huge_memory.c | 56 ++++++++++++++++++++++----------------------- 1 file changed, 28 insertions(+), 28 deletions(-) diff -puN mm/huge_memory.c~thp-reduce-indentation-level-in-change_huge_pmd mm/huge_memory.c --- a/mm/huge_memory.c~thp-reduce-indentation-level-in-change_huge_pmd +++ a/mm/huge_memory.c @@ -1724,37 +1724,37 @@ int change_huge_pmd(struct vm_area_struc { struct mm_struct *mm = vma->vm_mm; spinlock_t *ptl; - int ret = 0; + pmd_t entry; + bool preserve_write; + int ret; ptl = __pmd_trans_huge_lock(pmd, vma); - if (ptl) { - pmd_t entry; - bool preserve_write = prot_numa && pmd_write(*pmd); - ret = 1; - - /* - * Avoid trapping faults against the zero page. The read-only - * data is likely to be read-cached on the local CPU and - * local/remote hits to the zero page are not interesting. - */ - if (prot_numa && is_huge_zero_pmd(*pmd)) { - spin_unlock(ptl); - return ret; - } - - if (!prot_numa || !pmd_protnone(*pmd)) { - entry = pmdp_huge_get_and_clear_notify(mm, addr, pmd); - entry = pmd_modify(entry, newprot); - if (preserve_write) - entry = pmd_mk_savedwrite(entry); - ret = HPAGE_PMD_NR; - set_pmd_at(mm, addr, pmd, entry); - BUG_ON(vma_is_anonymous(vma) && !preserve_write && - pmd_write(entry)); - } - spin_unlock(ptl); - } + if (!ptl) + return 0; + preserve_write = prot_numa && pmd_write(*pmd); + ret = 1; + + /* + * Avoid trapping faults against the zero page. The read-only + * data is likely to be read-cached on the local CPU and + * local/remote hits to the zero page are not interesting. + */ + if (prot_numa && is_huge_zero_pmd(*pmd)) + goto unlock; + + if (prot_numa && pmd_protnone(*pmd)) + goto unlock; + + entry = pmdp_huge_get_and_clear_notify(mm, addr, pmd); + entry = pmd_modify(entry, newprot); + if (preserve_write) + entry = pmd_mk_savedwrite(entry); + ret = HPAGE_PMD_NR; + set_pmd_at(mm, addr, pmd, entry); + BUG_ON(vma_is_anonymous(vma) && !preserve_write && pmd_write(entry)); +unlock: + spin_unlock(ptl); return ret; } _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
