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Wed, 12 May 2021 17:58:25 -0700 (PDT) MIME-Version: 1.0 References: <921e53f3-4b13-aab8-4a9e-e83ff15371e4@nec.com> <701b3c80-b6f0-dcb3-7f3d-da6b74dfc1db@nec.com> In-Reply-To: <701b3c80-b6f0-dcb3-7f3d-da6b74dfc1db@nec.com> From: Yang Shi Date: Wed, 12 May 2021 17:58:13 -0700 Message-ID: Subject: Re: [REGRESSION v5.13-rc1] NULL dereference in do_shrink_slab() To: =?UTF-8?B?Tk9NVVJBIEpVTklDSEko6YeO5p2RIOa3s+S4gCk=?= Cc: Shakeel Butt , Tejun Heo , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "vbabka@suse.cz" , "ktkhai@virtuozzo.com" , "guro@fb.com" , "david@fromorbit.com" , "hannes@cmpxchg.org" , "mhocko@suse.com" , "akpm@linux-foundation.org" Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=gmail.com header.s=20161025 header.b="s6kvF/PE"; spf=pass (imf29.hostedemail.com: domain of shy828301@gmail.com designates 209.85.208.53 as permitted sender) smtp.mailfrom=shy828301@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 88AC5D5 X-Stat-Signature: 7zgwt68wd33y1naomffe1srfcn96hs7e Received-SPF: none (gmail.com>: No applicable sender policy available) receiver=imf29; identity=mailfrom; envelope-from=""; helo=mail-ed1-f53.google.com; client-ip=209.85.208.53 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1620867499-748211 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, May 12, 2021 at 5:10 PM NOMURA JUNICHI(=E9=87=8E=E6=9D=91=E3=80=80= =E6=B7=B3=E4=B8=80) wrote: > > On 2021/05/13 1:31, Yang Shi wrote: > > On Wed, May 12, 2021 at 5:36 AM Shakeel Butt wrot= e: > >> > >> +Tejun Heo > >> > >> On Wed, May 12, 2021 at 3:48 AM NOMURA JUNICHI(=E9=87=8E=E6=9D=91=E3= =80=80=E6=B7=B3=E4=B8=80) > >> wrote: > >>> With the commit 476b30a0949a, if a memcg-aware shrinker is registered= before > >>> cgroup_init(), shrinker->nr_deferred is NULL. However xchg_nr_deferr= ed() > >>> tries to use it as memcg is turned off via "cgroup_disable=3Dmemory". > >>> > >>> Any thoughts? > > > > Thanks for the report. > > > >> > >> Is there a way to find the call chain of "memcg-aware shrinker is > >> registered before cgroup_init()"? > > > > Other than adding some printk in prealloc_memcg_shrinker() then > > checking out the output of dmesg I didn't think of a better way. Not > > sure if we have something like early trace. > > This is the first registration of memcg-aware shrinker: > > [ 1.933693] Call Trace: > [ 1.934694] sget_fc+0x20d/0x2f0 > [ 1.935693] ? compare_single+0x10/0x10 > [ 1.936693] ? shmem_create+0x30/0x30 > [ 1.937693] vfs_get_super+0x3e/0x100 > [ 1.938693] get_tree_nodev+0x16/0x20 > [ 1.939693] shmem_get_tree+0x15/0x20 > [ 1.940693] vfs_get_tree+0x2a/0xc0 > [ 1.941693] fc_mount+0x12/0x40 > [ 1.942693] vfs_kern_mount.part.43+0x61/0xa0 > [ 1.943693] kern_mount+0x24/0x40 > [ 1.944693] shmem_init+0x5c/0xc8 > [ 1.945693] mnt_init+0x12f/0x24a > [ 1.946693] ? __percpu_counter_init+0x8f/0xb0 > [ 1.947693] vfs_caches_init+0xce/0xda > [ 1.948693] start_kernel+0x479/0x4e3 > [ 1.949693] x86_64_start_reservations+0x24/0x26 > [ 1.950693] x86_64_start_kernel+0x8a/0x8d > [ 1.951693] secondary_startup_64_no_verify+0xc2/0xcb > > That is done after command line parsing but before cgroup_init. Thanks for sharing the log. I was not aware that shmem is initialized and mounted so early. > > >> Irrespective I think we can revert a3e72739b7a7e ("cgroup: fix too > >> early usage of static_branch_disable()") as 6041186a3258 ("init: > >> initialize jump labels before command line option parsing") has moved > >> the initialization of jump labels before command line parsing. > > > > Seems make sense to me. If some memcg aware shrinker is registered > > before cgroup_init(), the mem_cgroup_disabled() check in > > prealloc_memcg_shrinker() would return false negative. And I don't > > think any shrinker could be registered before parsing boot > > commandline. > > Thank you. Shakeel 's patch works for me: > > [PATCH] cgroup: disable controllers at parse time > https://lore.kernel.org/linux-mm/20210512201946.2949351-1-shakeelb@goo= gle.com/ Thanks for running the test. > > -- > Jun'ichi Nomura, NEC Corporation / NEC Solution Innovators, Ltd.