From a54a407fbf7735fd8f7841375574f5d9b0375f93 Mon Sep 17 00:00:00 2001 From: Mel Gorman Date: Mon, 7 Oct 2013 11:28:46 +0100 Subject: mm: Close races between THP migration and PMD numa clearing THP migration uses the page lock to guard against parallel allocations but there are cases like this still open Task A Task B --------------------- --------------------- do_huge_pmd_numa_page do_huge_pmd_numa_page lock_page mpol_misplaced == -1 unlock_page goto clear_pmdnuma lock_page mpol_misplaced == 2 migrate_misplaced_transhuge pmd = pmd_mknonnuma set_pmd_at During hours of testing, one crashed with weird errors and while I have no direct evidence, I suspect something like the race above happened. This patch extends the page lock to being held until the pmd_numa is cleared to prevent migration starting in parallel while the pmd_numa is being cleared. It also flushes the old pmd entry and orders pagetable insertion before rmap insertion. Signed-off-by: Mel Gorman Reviewed-by: Rik van Riel Cc: Andrea Arcangeli Cc: Johannes Weiner Cc: Srikar Dronamraju Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/1381141781-10992-9-git-send-email-mgorman@suse.de Signed-off-by: Ingo Molnar --- mm/huge_memory.c | 33 +++++++++++++++------------------ 1 file changed, 15 insertions(+), 18 deletions(-) (limited to 'mm/huge_memory.c') diff --git a/mm/huge_memory.c b/mm/huge_memory.c index c3bb65f284d5..d4928769680f 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1304,24 +1304,25 @@ int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma, target_nid = mpol_misplaced(page, vma, haddr); if (target_nid == -1) { /* If the page was locked, there are no parallel migrations */ - if (page_locked) { - unlock_page(page); + if (page_locked) goto clear_pmdnuma; - } - /* Otherwise wait for potential migrations and retry fault */ + /* + * Otherwise wait for potential migrations and retry. We do + * relock and check_same as the page may no longer be mapped. + * As the fault is being retried, do not account for it. + */ spin_unlock(&mm->page_table_lock); wait_on_page_locked(page); + page_nid = -1; goto out; } /* Page is misplaced, serialise migrations and parallel THP splits */ get_page(page); spin_unlock(&mm->page_table_lock); - if (!page_locked) { + if (!page_locked) lock_page(page); - page_locked = true; - } anon_vma = page_lock_anon_vma_read(page); /* Confirm the PMD did not change while page_table_lock was released */ @@ -1329,32 +1330,28 @@ int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma, if (unlikely(!pmd_same(pmd, *pmdp))) { unlock_page(page); put_page(page); + page_nid = -1; goto out_unlock; } - /* Migrate the THP to the requested node */ + /* + * Migrate the THP to the requested node, returns with page unlocked + * and pmd_numa cleared. + */ spin_unlock(&mm->page_table_lock); migrated = migrate_misplaced_transhuge_page(mm, vma, pmdp, pmd, addr, page, target_nid); if (migrated) page_nid = target_nid; - else - goto check_same; goto out; - -check_same: - spin_lock(&mm->page_table_lock); - if (unlikely(!pmd_same(pmd, *pmdp))) { - /* Someone else took our fault */ - page_nid = -1; - goto out_unlock; - } clear_pmdnuma: + BUG_ON(!PageLocked(page)); pmd = pmd_mknonnuma(pmd); set_pmd_at(mm, haddr, pmdp, pmd); VM_BUG_ON(pmd_numa(*pmdp)); update_mmu_cache_pmd(vma, addr, pmdp); + unlock_page(page); out_unlock: spin_unlock(&mm->page_table_lock); -- cgit v1.2.3-55-g7522