From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: [PATCH] memcg: add RCU locking around css_for_each_descendant_pre() in memcg_offline_kmem() Date: Thu, 26 May 2016 16:30:18 -0400 Message-ID: <20160526203018.GG23194@mtj.duckdns.org> Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=sender:date:from:to:cc:subject:message-id:mime-version :content-disposition:content-transfer-encoding:user-agent; bh=fEvIuWU1zHx+PAn6F4QtypVDmTJkik+1mCs7I7TkZmc=; b=i/HS2WHY71fVuZzErpXmlaS15E3nmzg7VHzIfjgnU0dtE1y/xQ4cJy7HzKThKbx0TJ Hnjzksz25tPnhEMY1zJj0353mi1O7ZjH0v38hFmKfH1yUvNxaDj/IsFWfUXOtdKc2bWA 0kBMrrC4Qbk3Gj3BR1A3X5U+X2Eble2D+VkViKCsLcuFs6ljm15j3Zn0/6VZcLHqFVld NlaxitDRqCDhi6CJypnXh+gyAwMSmHmJK6bP67H9Mfm5/FU5EEizC8vGl2A1+C8RBNN0 GZKdib1OOxbRZ+AayryvUe5xas57lNVDAVzdbmZZs/bPdiaCsZ7mqeKkKUO4651zIZip yn+A== Content-Disposition: inline Sender: owner-linux-mm@kvack.org List-ID: Content-Type: text/plain; charset="utf-8" To: Johannes Weiner , Michal Hocko , Vladimir Davydov , Andrew Morton Cc: cgroups@vger.kernel.org, linux-mm@kvack.org, kernel-team@fb.com memcg_offline_kmem() may be called from memcg_free_kmem() after a css init failure. memcg_free_kmem() is a ->css_free callback which is called without cgroup_mutex and memcg_offline_kmem() ends up using css_for_each_descendant_pre() without any locking. Fix it by adding rcu read locking around it. mkdir: cannot create directory =E2=80=9865530=E2=80=99: No space left on= device [ 527.241361] =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D [ 527.241845] [ INFO: suspicious RCU usage. ] [ 527.242367] 4.6.0-work+ #321 Not tainted [ 527.242730] ------------------------------- [ 527.243220] kernel/cgroup.c:4008 cgroup_mutex or RCU read lock requir= ed! [ 527.243970] [ 527.243970] other info that might help us debug this: [ 527.243970] [ 527.244715] [ 527.244715] rcu_scheduler_active =3D 1, debug_locks =3D 0 [ 527.245463] 2 locks held by kworker/0:5/1664: [ 527.245939] #0: ("cgroup_destroy"){.+.+..}, at: [= ] process_one_work+0x165/0x4a0 [ 527.246958] #1: ((&css->destroy_work)#3){+.+...}, at: [] process_one_work+0x165/0x4a0 [ 527.248098] [ 527.248098] stack backtrace: [ 527.249565] CPU: 0 PID: 1664 Comm: kworker/0:5 Not tainted 4.6.0-work= + #321 [ 527.250429] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BI= OS 1.9.1-1.fc24 04/01/2014 [ 527.250555] Workqueue: cgroup_destroy css_free_work_fn [ 527.250555] 0000000000000000 ffff880178747c68 ffffffff8128bfc7 ffff8= 80178b8ac40 [ 527.250555] 0000000000000001 ffff880178747c98 ffffffff8108c297 00000= 00000000000 [ 527.250555] ffff88010de54138 000000000000fffb ffff88010de537e8 ffff8= 80178747cc0 [ 527.250555] Call Trace: [ 527.250555] [] dump_stack+0x68/0xa1 [ 527.250555] [] lockdep_rcu_suspicious+0xd7/0x110 [ 527.250555] [] css_next_descendant_pre+0x7d/0xb0 [ 527.250555] [] memcg_offline_kmem.part.44+0x4a/0xc= 0 [ 527.250555] [] mem_cgroup_css_free+0x1ec/0x200 [ 527.250555] [] css_free_work_fn+0x49/0x5e0 [ 527.250555] [] process_one_work+0x1c5/0x4a0 [ 527.250555] [] ? process_one_work+0x165/0x4a0 [ 527.250555] [] worker_thread+0x49/0x490 [ 527.250555] [] ? process_one_work+0x4a0/0x4a0 [ 527.250555] [] ? process_one_work+0x4a0/0x4a0 [ 527.250555] [] kthread+0xea/0x100 [ 527.250555] [] ret_from_fork+0x1f/0x40 [ 527.250555] [] ? kthread_create_on_node+0x200/0x20= 0 Signed-off-by: Tejun Heo --- mm/memcontrol.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index cf428d7..8d42c6d 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2892,6 +2892,7 @@ static void memcg_offline_kmem(struct mem_cgroup *m= emcg) * ordering is imposed by list_lru_node->lock taken by * memcg_drain_all_list_lrus(). */ + rcu_read_lock(); /* can be called from css_free w/o cgroup_mutex */ css_for_each_descendant_pre(css, &memcg->css) { child =3D mem_cgroup_from_css(css); BUG_ON(child->kmemcg_id !=3D kmemcg_id); @@ -2899,6 +2900,8 @@ static void memcg_offline_kmem(struct mem_cgroup *m= emcg) if (!memcg->use_hierarchy) break; } + rcu_read_unlock(); + memcg_drain_all_list_lrus(kmemcg_id, parent->kmemcg_id); =20 memcg_free_cache_id(kmemcg_id); -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org