From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx186.postini.com [74.125.245.186]) by kanga.kvack.org (Postfix) with SMTP id 448316B005D for ; Tue, 25 Sep 2012 14:11:25 -0400 (EDT) From: Andrea Arcangeli Subject: [PATCH] thp: avoid VM_BUG_ON page_count(page) false positives in __collapse_huge_page_copy Date: Tue, 25 Sep 2012 20:11:18 +0200 Message-Id: <1348596678-2768-2-git-send-email-aarcange@redhat.com> In-Reply-To: <1348596678-2768-1-git-send-email-aarcange@redhat.com> References: <1348596678-2768-1-git-send-email-aarcange@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: linux-mm@kvack.org, Rik van Riel , Johannes Weiner , Hugh Dickins , Mel Gorman , Petr Holasek Use page_freeze_refs to prevent speculative pagecache lookups to trigger the false positives, so we're still able to check the page_count to be exact. Signed-off-by: Andrea Arcangeli --- mm/huge_memory.c | 19 ++++++++++++++++++- 1 files changed, 18 insertions(+), 1 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 1598708..7eca652 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1704,6 +1704,9 @@ void __khugepaged_exit(struct mm_struct *mm) static void release_pte_page(struct page *page) { +#ifdef CONFIG_DEBUG_VM + page_unfreeze_refs(page, 2); +#endif /* 0 stands for page_is_file_cache(page) == false */ dec_zone_page_state(page, NR_ISOLATED_ANON + 0); unlock_page(page); @@ -1784,6 +1787,20 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, VM_BUG_ON(!PageLocked(page)); VM_BUG_ON(PageLRU(page)); +#ifdef CONFIG_DEBUG_VM + /* + * For the VM_BUG_ON check on page_count(page) in + * __collapse_huge_page_copy not to trigger false + * positives we've to prevent the speculative + * pagecache lookups too with page_freeze_refs. We + * could check for >= 2 instead but this provides for + * a more strict debugging behavior. + */ + if (!page_freeze_refs(page, 2)) { + release_pte_pages(pte, _pte+1); + goto out; + } +#endif /* If there is no mapped pte young don't collapse the page */ if (pte_young(pteval) || PageReferenced(page) || mmu_notifier_test_young(vma->vm_mm, address)) @@ -1814,7 +1831,7 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page, src_page = pte_page(pteval); copy_user_highpage(page, src_page, address, vma); VM_BUG_ON(page_mapcount(src_page) != 1); - VM_BUG_ON(page_count(src_page) != 2); + VM_BUG_ON(page_count(src_page) != 0); release_pte_page(src_page); /* * ptl mostly unnecessary, but preempt has to -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org