From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.7 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E79E7C43441 for ; Tue, 13 Nov 2018 05:51:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AA1C322510 for ; Tue, 13 Nov 2018 05:51:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="skOW9FC4" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AA1C322510 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732397AbeKMPsF (ORCPT ); Tue, 13 Nov 2018 10:48:05 -0500 Received: from mail.kernel.org ([198.145.29.99]:34186 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730922AbeKMPsE (ORCPT ); Tue, 13 Nov 2018 10:48:04 -0500 Received: from sasha-vm.mshome.net (unknown [64.114.255.114]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0820522510; Tue, 13 Nov 2018 05:51:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1542088297; bh=N6As6j6xCoPMaQzs4R/SYfp9cNiF7iuDlMLJPddbhIE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=skOW9FC48TgHb3LX9LE2GNXi9bg+8QOZPZx3WWr6IThlhoDplE/3fTrOxztxe+zRd VcyHQL/q7oBVOZx/G8L5CqIwNNsrC+rFnHJPiRk/OIPWJPitraZfpcwB0QfZZqNroW 3kbdOQpIKyY4K4lIiGOJ/aVaomg8v4hN2WHggjVA= From: Sasha Levin To: stable@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Andrea Arcangeli , Jerome Glisse , Andrew Morton , Linus Torvalds , Sasha Levin , linux-mm@kvack.org Subject: [PATCH AUTOSEL 4.18 33/39] mm: thp: fix MADV_DONTNEED vs migrate_misplaced_transhuge_page race condition Date: Tue, 13 Nov 2018 00:50:47 -0500 Message-Id: <20181113055053.78352-33-sashal@kernel.org> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20181113055053.78352-1-sashal@kernel.org> References: <20181113055053.78352-1-sashal@kernel.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Andrea Arcangeli [ Upstream commit d7c3393413fe7e7dc54498ea200ea94742d61e18 ] Patch series "migrate_misplaced_transhuge_page race conditions". Aaron found a new instance of the THP MADV_DONTNEED race against pmdp_clear_flush* variants, that was apparently left unfixed. While looking into the race found by Aaron, I may have found two more issues in migrate_misplaced_transhuge_page. These race conditions would not cause kernel instability, but they'd corrupt userland data or leave data non zero after MADV_DONTNEED. I did only minor testing, and I don't expect to be able to reproduce this (especially the lack of ->invalidate_range before migrate_page_copy, requires the latest iommu hardware or infiniband to reproduce). The last patch is noop for x86 and it needs further review from maintainers of archs that implement flush_cache_range() (not in CC yet). To avoid confusion, it's not the first patch that introduces the bug fixed in the second patch, even before removing the pmdp_huge_clear_flush_notify, that _notify suffix was called after migrate_page_copy already run. This patch (of 3): This is a corollary of ced108037c2aa ("thp: fix MADV_DONTNEED vs. numa balancing race"), 58ceeb6bec8 ("thp: fix MADV_DONTNEED vs. MADV_FREE race") and 5b7abeae3af8c ("thp: fix MADV_DONTNEED vs clear soft dirty race). When the above three fixes where posted Dave asked https://lkml.kernel.org/r/929b3844-aec2-0111-fef7-8002f9d4e2b9@intel.com but apparently this was missed. The pmdp_clear_flush* in migrate_misplaced_transhuge_page() was introduced in a54a407fbf7 ("mm: Close races between THP migration and PMD numa clearing"). The important part of such commit is only the part where the page lock is not released until the first do_huge_pmd_numa_page() finished disarming the pagenuma/protnone. The addition of pmdp_clear_flush() wasn't beneficial to such commit and there's no commentary about such an addition either. I guess the pmdp_clear_flush() in such commit was added just in case for safety, but it ended up introducing the MADV_DONTNEED race condition found by Aaron. At that point in time nobody thought of such kind of MADV_DONTNEED race conditions yet (they were fixed later) so the code may have looked more robust by adding the pmdp_clear_flush(). This specific race condition won't destabilize the kernel, but it can confuse userland because after MADV_DONTNEED the memory won't be zeroed out. This also optimizes the code and removes a superfluous TLB flush. [akpm@linux-foundation.org: reflow comment to 80 cols, fix grammar and typo (beacuse)] Link: http://lkml.kernel.org/r/20181013002430.698-2-aarcange@redhat.com Signed-off-by: Andrea Arcangeli Reported-by: Aaron Tomlin Acked-by: Mel Gorman Acked-by: Kirill A. Shutemov Cc: Jerome Glisse Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- mm/migrate.c | 25 ++++++++++++++++++------- 1 file changed, 18 insertions(+), 7 deletions(-) diff --git a/mm/migrate.c b/mm/migrate.c index f49eb9589d73..38ad6365ed10 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -2086,15 +2086,26 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm, entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma); /* - * Clear the old entry under pagetable lock and establish the new PTE. - * Any parallel GUP will either observe the old page blocking on the - * page lock, block on the page table lock or observe the new page. - * The SetPageUptodate on the new page and page_add_new_anon_rmap - * guarantee the copy is visible before the pagetable update. + * Overwrite the old entry under pagetable lock and establish + * the new PTE. Any parallel GUP will either observe the old + * page blocking on the page lock, block on the page table + * lock or observe the new page. The SetPageUptodate on the + * new page and page_add_new_anon_rmap guarantee the copy is + * visible before the pagetable update. */ flush_cache_range(vma, mmun_start, mmun_end); page_add_anon_rmap(new_page, vma, mmun_start, true); - pmdp_huge_clear_flush_notify(vma, mmun_start, pmd); + /* + * At this point the pmd is numa/protnone (i.e. non present) and the TLB + * has already been flushed globally. So no TLB can be currently + * caching this non present pmd mapping. There's no need to clear the + * pmd before doing set_pmd_at(), nor to flush the TLB after + * set_pmd_at(). Clearing the pmd here would introduce a race + * condition against MADV_DONTNEED, because MADV_DONTNEED only holds the + * mmap_sem for reading. If the pmd is set to NULL at any given time, + * MADV_DONTNEED won't wait on the pmd lock and it'll skip clearing this + * pmd. + */ set_pmd_at(mm, mmun_start, pmd, entry); update_mmu_cache_pmd(vma, address, &entry); @@ -2108,7 +2119,7 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm, * No need to double call mmu_notifier->invalidate_range() callback as * the above pmdp_huge_clear_flush_notify() did already call it. */ - mmu_notifier_invalidate_range_only_end(mm, mmun_start, mmun_end); + mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end); /* Take an "isolate" reference and put new page on the LRU. */ get_page(new_page); -- 2.17.1