From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f72.google.com (mail-ed1-f72.google.com [209.85.208.72]) by kanga.kvack.org (Postfix) with ESMTP id 6681F6B04C3 for ; Tue, 30 Oct 2018 02:12:55 -0400 (EDT) Received: by mail-ed1-f72.google.com with SMTP id w42-v6so8675612edd.0 for ; Mon, 29 Oct 2018 23:12:55 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id p14-v6si596600edi.343.2018.10.29.23.12.53 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 29 Oct 2018 23:12:53 -0700 (PDT) Date: Tue, 30 Oct 2018 07:12:49 +0100 From: Michal Hocko Subject: Re: [PATCH] mm: handle no memcg case in memcg_kmem_charge() properly Message-ID: <20181030061249.GS32673@dhcp22.suse.cz> References: <20181029215123.17830-1-guro@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181029215123.17830-1-guro@fb.com> Sender: owner-linux-mm@kvack.org List-ID: To: Roman Gushchin Cc: "linux-mm@kvack.org" , Mike Galbraith , "linux-kernel@vger.kernel.org" , Kernel Team , Johannes Weiner , Vladimir Davydov , Andrew Morton , Shakeel Butt 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=memory" boot option: the system panics with the > following stack trace: > > [0.928542] BUG: unable to handle kernel NULL pointer dereference at 00000000000000f8 > [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+ #410 > [0.930637] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-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 84 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: 0000000000000000 > [0.935558] RDX: ffffacf68031fd08 RSI: 0000000000000020 RDI: 00000000000000f8 > [0.936288] RBP: 0000000000000001 R08: 8000000000000063 R09: ffff99ff7cd37a40 > [0.937021] R10: ffffacf68031fed0 R11: 0000000000200000 R12: 0000000000000020 > [0.937749] R13: ffffacf68031fd08 R14: 00000000000000f8 R15: ffff99ff7da1ec60 > [0.938486] FS: 00007fc2140bb280(0000) GS:ffff99ff7da00000(0000) knlGS:0000000000000000 > [0.939311] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [0.939905] CR2: 00000000000000f8 CR3: 0000000012dc8002 CR4: 0000000000760ef0 > [0.940638] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > [0.941366] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > [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 > > 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. > > 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 I tend to agree with Shakeel that consistency with the other caller would be less confusing. 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. Acked-by: Michal Hocko > --- > mm/memcontrol.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 54920cbc46bf..6e1469b80cb7 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2593,7 +2593,7 @@ int memcg_kmem_charge(struct page *page, gfp_t gfp, int order) > struct mem_cgroup *memcg; > int ret = 0; > > - if (memcg_kmem_bypass()) > + if (mem_cgroup_disabled() || memcg_kmem_bypass()) > return 0; > > memcg = get_mem_cgroup_from_current(); > -- > 2.17.2 -- Michal Hocko SUSE Labs