From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yw1-f72.google.com (mail-yw1-f72.google.com [209.85.161.72]) by kanga.kvack.org (Postfix) with ESMTP id 0039E6B02A8 for ; Tue, 30 Oct 2018 11:56:14 -0400 (EDT) Received: by mail-yw1-f72.google.com with SMTP id r132-v6so9064716ywg.21 for ; Tue, 30 Oct 2018 08:56:14 -0700 (PDT) Received: from mx0a-00082601.pphosted.com (mx0a-00082601.pphosted.com. [67.231.145.42]) by mx.google.com with ESMTPS id u62-v6si14469431ybb.380.2018.10.30.08.56.13 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 30 Oct 2018 08:56:13 -0700 (PDT) From: Roman Gushchin Subject: Re: [PATCH] mm: handle no memcg case in memcg_kmem_charge() properly Date: Tue, 30 Oct 2018 15:55:39 +0000 Message-ID: <20181030155532.GA17612@tower.DHCP.thefacebook.com> References: <20181029215123.17830-1-guro@fb.com> <20181030061249.GS32673@dhcp22.suse.cz> In-Reply-To: <20181030061249.GS32673@dhcp22.suse.cz> Content-Language: en-US Content-Type: text/plain; charset="us-ascii" Content-ID: <65515EED1E43F74C8166BE9C00A911E0@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: "linux-mm@kvack.org" , Mike Galbraith , "linux-kernel@vger.kernel.org" , Kernel Team , Johannes Weiner , Vladimir Davydov , Andrew Morton , Shakeel Butt On Tue, Oct 30, 2018 at 07:12:49AM +0100, Michal Hocko wrote: > On Mon 29-10-18 21:51:55, Roman Gushchin wrote: > > Mike Galbraith reported a regression caused by the commit 9b6f7e163cd0 > > ("mm: rework memcg kernel stack accounting") on a system with > > "cgroup_disable=3Dmemory" boot option: the system panics with the > > following stack trace: > >=20 > > [0.928542] BUG: unable to handle kernel NULL pointer dereference at 0= 0000000000000f8 > > [0.929317] PGD 0 P4D 0 > > [0.929573] Oops: 0002 [#1] PREEMPT SMP PTI > > [0.929984] CPU: 0 PID: 1 Comm: systemd Not tainted 4.19.0-preempt+ #4= 10 > > [0.930637] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIO= S ?-20180531_142017-buildhw-08.phx2.fed4 > > [0.931862] RIP: 0010:page_counter_try_charge+0x22/0xc0 > > [0.932376] Code: 41 5d c3 c3 0f 1f 40 00 0f 1f 44 00 00 48 85 ff 0f 8= 4 a7 00 00 00 41 56 48 89 f8 49 89 fe 49 > > [0.934283] RSP: 0018:ffffacf68031fcb8 EFLAGS: 00010202 > > [0.934826] RAX: 00000000000000f8 RBX: 0000000000000000 RCX: 000000000= 0000000 > > [0.935558] RDX: ffffacf68031fd08 RSI: 0000000000000020 RDI: 000000000= 00000f8 > > [0.936288] RBP: 0000000000000001 R08: 8000000000000063 R09: ffff99ff7= cd37a40 > > [0.937021] R10: ffffacf68031fed0 R11: 0000000000200000 R12: 000000000= 0000020 > > [0.937749] R13: ffffacf68031fd08 R14: 00000000000000f8 R15: ffff99ff7= da1ec60 > > [0.938486] FS: 00007fc2140bb280(0000) GS:ffff99ff7da00000(0000) knlG= S:0000000000000000 > > [0.939311] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > [0.939905] CR2: 00000000000000f8 CR3: 0000000012dc8002 CR4: 000000000= 0760ef0 > > [0.940638] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 000000000= 0000000 > > [0.941366] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 000000000= 0000400 > > [0.942110] PKRU: 55555554 > > [0.942412] Call Trace: > > [0.942673] try_charge+0xcb/0x780 > > [0.943031] memcg_kmem_charge_memcg+0x28/0x80 > > [0.943486] ? __vmalloc_node_range+0x1e4/0x280 > > [0.943971] memcg_kmem_charge+0x8b/0x1d0 > > [0.944396] copy_process.part.41+0x1ca/0x2070 > > [0.944853] ? get_acl+0x1a/0x120 > > [0.945200] ? shmem_tmpfile+0x90/0x90 > > [0.945596] _do_fork+0xd7/0x3d0 > > [0.945934] ? trace_hardirqs_off_thunk+0x1a/0x1c > > [0.946421] do_syscall_64+0x5a/0x180 > > [0.946798] entry_SYSCALL_64_after_hwframe+0x49/0xbe > >=20 > > The problem occurs because get_mem_cgroup_from_current() returns > > the NULL pointer if memory controller is disabled. Let's check > > if this is a case at the beginning of memcg_kmem_charge() and > > just return 0 if mem_cgroup_disabled() returns true. This is how > > we handle this case in many other places in the memory controller > > code. > >=20 > > Fixes: 9b6f7e163cd0 ("mm: rework memcg kernel stack accounting") > > Reported-by: Mike Galbraith > > Signed-off-by: Roman Gushchin > > Cc: Michal Hocko > > Cc: Johannes Weiner > > Cc: Vladimir Davydov > > Cc: Andrew Morton >=20 > I tend to agree with Shakeel that consistency with the other caller > would be less confusing. I totally agree that consistency is a thing here (and everywhere), however using memcg_kmem_enabled() here is not consistent at all. memcg_kmem_enabled() is tight to the slab allocation accounting, but here we have a different type of allocation: we actually charge an area preallocated using vmalloc. > I would split the function to __memcg_kmem_charge > without any checks and call it from __alloc_pages_nodemask and add the > check to memcg_kmem_charge. This would be less confusing I guess. > Something for a follow up clean up though. Sure. Alternatively, we can check the pointer returned by get_mem_cgroup_from_current() in memcg_kmem_charge(). Anyway, let's postpone this clean up a bit, now the main goal is to fix the panic. > Acked-by: Michal Hocko Thanks! -- Andrew, can you, please, pull this patch to 4.20-rc1 or -rc2? It has been acked by Rik and Michal, and tested by Mike. Thanks!