From patchwork Fri Jun 26 03:30:16 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 223001 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=-4.0 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 D4B20C433DF for ; Fri, 26 Jun 2020 03:30:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B0E0D2089D for ; Fri, 26 Jun 2020 03:30:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593142218; bh=TPo1UrcUMcQLfguhSa0tPlCmgq3675PgjU4unLb12E8=; h=Date:From:To:Subject:In-Reply-To:List-ID:From; b=hsX/XXVEHxOeEVT7FD+uXl/lzzm1gqN5NFeyQGcL7s1h339VpdebRNIq6/Qj5OidT /HBZJ10rFkTh5hcwDE26b4u0bmq0cSwrXYZJIKCorgc42o9x9YNuIa0OO3j8NR4xrE tGxmVh2vJijDNyL2Y/AdoTtZjWfF38+LyzjWTL38= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728370AbgFZDaS (ORCPT ); Thu, 25 Jun 2020 23:30:18 -0400 Received: from mail.kernel.org ([198.145.29.99]:48536 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728333AbgFZDaR (ORCPT ); Thu, 25 Jun 2020 23:30:17 -0400 Received: from localhost.localdomain (c-71-198-47-131.hsd1.ca.comcast.net [71.198.47.131]) (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 00FD52053B; Fri, 26 Jun 2020 03:30:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593142217; bh=TPo1UrcUMcQLfguhSa0tPlCmgq3675PgjU4unLb12E8=; h=Date:From:To:Subject:In-Reply-To:From; b=a0TzQHUxvXv621WwiBagpR+kfSJ9K7omrQxguyL8NqxTGDC/UjZZoIR/59x37Tawb tD0eRpU8n+MXd6kY5RhPRKgWgdCJ7L7yYX7qYVbwHGiElp0MrVsfuWclHKARk3PzxH 0h+qzXDOz4UogLk1kWWwhircHlo4r8sNclacNJQs= Date: Thu, 25 Jun 2020 20:30:16 -0700 From: Andrew Morton To: akpm@linux-foundation.org, chris@chrisdown.name, guro@fb.com, hannes@cmpxchg.org, mhocko@suse.com, mm-commits@vger.kernel.org, stable@vger.kernel.org, tj@kernel.org, torvalds@linux-foundation.org Subject: [patch 20/32] mm: memcontrol: handle div0 crash race condition in memory.low Message-ID: <20200626033016.7z3uIdJCS%akpm@linux-foundation.org> In-Reply-To: <20200625202807.b630829d6fa55388148bee7d@linux-foundation.org> User-Agent: s-nail v14.8.16 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 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;