4.4-stable review patch. If anyone has any objections, please let me know.
------------------ From: Kirill A. Shutemov <kirill.shute...@linux.intel.com> commit 0a85e51d37645e9ce57e5e1a30859e07810ed07c upstream. 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.shute...@linux.intel.com Signed-off-by: Kirill A. Shutemov <kirill.shute...@linux.intel.com> Acked-by: Vlastimil Babka <vba...@suse.cz> Cc: Andrea Arcangeli <aarca...@redhat.com> Cc: Hillf Danton <hillf...@alibaba-inc.com> Cc: <sta...@vger.kernel.org> Signed-off-by: Andrew Morton <a...@linux-foundation.org> Signed-off-by: Linus Torvalds <torva...@linux-foundation.org> [jwang: adjust context for 4.4 kernel] Signed-off-by: Jack Wang <jinpu.w...@profitbricks.com> Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org> --- mm/huge_memory.c | 54 ++++++++++++++++++++++++++++-------------------------- 1 file changed, 28 insertions(+), 26 deletions(-) --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1566,35 +1566,37 @@ int change_huge_pmd(struct vm_area_struc { struct mm_struct *mm = vma->vm_mm; spinlock_t *ptl; + pmd_t entry; + bool preserve_write; + int ret = 0; - if (__pmd_trans_huge_lock(pmd, vma, &ptl) == 1) { - 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_mkwrite(entry); - ret = HPAGE_PMD_NR; - set_pmd_at(mm, addr, pmd, entry); - BUG_ON(!preserve_write && pmd_write(entry)); - } - spin_unlock(ptl); - } + if (__pmd_trans_huge_lock(pmd, vma, &ptl) != 1) + 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_mkwrite(entry); + ret = HPAGE_PMD_NR; + set_pmd_at(mm, addr, pmd, entry); + BUG_ON(!preserve_write && pmd_write(entry)); +unlock: + spin_unlock(ptl); return ret; }
