From patchwork Tue Jun 16 19:17:56 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 224303 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=-3.8 required=3.0 tests=DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED autolearn=no 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 AC7E8C433E0 for ; Tue, 16 Jun 2020 19:17:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 82DED207C4 for ; Tue, 16 Jun 2020 19:17:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592335079; bh=nCgo+CjpHOtgCxIgrlceHN2BrKfO7m2O0K6WoI72MSI=; h=Date:From:To:Subject:List-ID:From; b=nkzY4ig7YWat/Skf91CkYqGuzuoxDTMBop+MzozHddrSDNAFheX70xK8LIicd2Wtw au4iVhlwUiOTBi3u5RAoipSdH0MwzO6GgIPQv0G2xvDc9Uv4Nfw5AeLVD4IBqIPKYt DoJUNx+P/NLEIIBpeBNxItDHunn25HK04yBiZInI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730175AbgFPTR7 (ORCPT ); Tue, 16 Jun 2020 15:17:59 -0400 Received: from mail.kernel.org ([198.145.29.99]:33548 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728861AbgFPTR6 (ORCPT ); Tue, 16 Jun 2020 15:17:58 -0400 Received: from X1 (nat-ab2241.sltdut.senawave.net [162.218.216.4]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9A85820776; Tue, 16 Jun 2020 19:17:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592335076; bh=nCgo+CjpHOtgCxIgrlceHN2BrKfO7m2O0K6WoI72MSI=; h=Date:From:To:Subject:From; b=mRQ+vE/YeDvJN95LClh99D4mYHX8tQjs4MUVAyqRVWuvAz6jcRWtuQe+gm+ASwgxH FcICa6iNo40km2M9NXMQ33xX1r7VyejB15CRnY70u2YA/8w9J7FXLXJXtoknYyik4x RqlMYOjiSMm+7tK9aHPdigJT4TTDWz7rSFrur6sc= Date: Tue, 16 Jun 2020 12:17:56 -0700 From: akpm@linux-foundation.org To: mm-commits@vger.kernel.org, tj@kernel.org, stable@vger.kernel.org, mhocko@suse.com, guro@fb.com, chris@chrisdown.name, hannes@cmpxchg.org Subject: + mm-memcontrol-handle-div0-crash-race-condition-in-memorylow.patch added to -mm tree Message-ID: <20200616191756.mnaoS%akpm@linux-foundation.org> User-Agent: s-nail v14.9.10 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org The patch titled Subject: mm: memcontrol: handle div0 crash race condition in memory.low has been added to the -mm tree. Its filename is mm-memcontrol-handle-div0-crash-race-condition-in-memorylow.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/mm-memcontrol-handle-div0-crash-race-condition-in-memorylow.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/mm-memcontrol-handle-div0-crash-race-condition-in-memorylow.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Johannes Weiner Subject: mm: memcontrol: handle div0 crash race condition in memory.low Tejun reports seeing rare div0 crashes in memory.low stress testing: [37228.504582] RIP: 0010:mem_cgroup_calculate_protection+0xed/0x150 [37228.505059] Code: 0f 46 d1 4c 39 d8 72 57 f6 05 16 d6 42 01 40 74 1f 4c 39 d8 76 1a 4c 39 d1 76 15 4c 29 d1 4c 29 d8 4d 29 d9 31 d2 48 0f af c1 <49> f7 f1 49 01 c2 4c 89 96 38 01 00 00 5d c3 48 0f af c7 31 d2 49 [37228.506254] RSP: 0018:ffffa14e01d6fcd0 EFLAGS: 00010246 [37228.506769] RAX: 000000000243e384 RBX: 0000000000000000 RCX: 0000000000008f4b [37228.507319] RDX: 0000000000000000 RSI: ffff8b89bee84000 RDI: 0000000000000000 [37228.507869] RBP: ffffa14e01d6fcd0 R08: ffff8b89ca7d40f8 R09: 0000000000000000 [37228.508376] R10: 0000000000000000 R11: 00000000006422f7 R12: 0000000000000000 [37228.508881] R13: ffff8b89d9617000 R14: ffff8b89bee84000 R15: ffffa14e01d6fdb8 [37228.509397] FS: 0000000000000000(0000) GS:ffff8b8a1f1c0000(0000) knlGS:0000000000000000 [37228.509917] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [37228.510442] CR2: 00007f93b1fc175b CR3: 000000016100a000 CR4: 0000000000340ea0 [37228.511076] Call Trace: [37228.511561] shrink_node+0x1e5/0x6c0 [37228.512044] balance_pgdat+0x32d/0x5f0 [37228.512521] kswapd+0x1d7/0x3d0 [37228.513346] ? wait_woken+0x80/0x80 [37228.514170] kthread+0x11c/0x160 [37228.514983] ? balance_pgdat+0x5f0/0x5f0 [37228.515797] ? kthread_park+0x90/0x90 [37228.516593] ret_from_fork+0x1f/0x30 This happens when parent_usage == siblings_protected. We check that usage is bigger than protected, which should imply parent_usage being bigger than siblings_protected. However, we don't read (or even update) these values atomically, and they can be out of sync as the memory state changes under us. A bit of fluctuation around the target protection isn't a big deal, but we need to handle the div0 case. Check the parent state explicitly to make sure we have a reasonable positive value for the divisor. Link: http://lkml.kernel.org/r/20200615140658.601684-1-hannes@cmpxchg.org Fixes: 8a931f801340 ("mm: memcontrol: recursive memory.low protection") Signed-off-by: Johannes Weiner Reported-by: Tejun Heo Acked-by: Michal Hocko Acked-by: Chris Down Cc: Roman Gushchin Cc: Signed-off-by: Andrew Morton --- mm/memcontrol.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) --- a/mm/memcontrol.c~mm-memcontrol-handle-div0-crash-race-condition-in-memorylow +++ a/mm/memcontrol.c @@ -6360,11 +6360,16 @@ static unsigned long effective_protectio * We're using unprotected memory for the weight so that if * some cgroups DO claim explicit protection, we don't protect * the same bytes twice. + * + * Check both usage and parent_usage against the respective + * protected values. One should imply the other, but they + * aren't read atomically - make sure the division is sane. */ if (!(cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_RECURSIVE_PROT)) return ep; - - if (parent_effective > siblings_protected && usage > protected) { + if (parent_effective > siblings_protected && + parent_usage > siblings_protected && + usage > protected) { unsigned long unclaimed; unclaimed = parent_effective - siblings_protected;