From a590b90d472f2c176c140576ee3ab44df7f67839 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 28 Apr 2017 15:14:55 -0400 Subject: [PATCH] cgroup: fix spurious warnings on cgroup_is_dead() from cgroup_sk_alloc() cgroup_get() expected to be called only on live cgroups and triggers warning on a dead cgroup; however, cgroup_sk_alloc() may be called while cloning a socket which is left in an empty and removed cgroup and thus may legitimately duplicate its reference on a dead cgroup. This currently triggers the following warning spuriously. WARNING: CPU: 14 PID: 0 at kernel/cgroup.c:490 cgroup_get+0x55/0x60 ... [] __warn+0xd3/0xf0 [] warn_slowpath_null+0x1e/0x20 [] cgroup_get+0x55/0x60 [] cgroup_sk_alloc+0x51/0xe0 [] sk_clone_lock+0x2db/0x390 [] inet_csk_clone_lock+0x16/0xc0 [] tcp_create_openreq_child+0x23/0x4b0 [] tcp_v6_syn_recv_sock+0x91/0x670 [] tcp_check_req+0x3a6/0x4e0 [] tcp_v6_rcv+0x693/0xa00 [] ip6_input_finish+0x59/0x3e0 [] ip6_input+0x32/0xb0 [] ip6_rcv_finish+0x57/0xa0 [] ipv6_rcv+0x318/0x4d0 [] __netif_receive_skb_core+0x2d7/0x9a0 [] __netif_receive_skb+0x16/0x70 [] netif_receive_skb_internal+0x23/0x80 [] napi_gro_frags+0x208/0x270 [] mlx4_en_process_rx_cq+0x74c/0xf40 [] mlx4_en_poll_rx_cq+0x30/0x90 [] net_rx_action+0x210/0x350 [] __do_softirq+0x106/0x2c7 [] irq_exit+0x9d/0xa0 [] do_IRQ+0x54/0xd0 [] common_interrupt+0x7f/0x7f [] cpuidle_enter+0x17/0x20 [] cpu_startup_entry+0x2a9/0x2f0 [] start_secondary+0xf1/0x100 This patch renames the existing cgroup_get() with the dead cgroup warning to cgroup_get_live() after cgroup_kn_lock_live() and introduces the new cgroup_get() which doesn't check whether the cgroup is live or dead. All existing cgroup_get() users except for cgroup_sk_alloc() are converted to use cgroup_get_live(). Fixes: d979a39d7242 ("cgroup: duplicate cgroup reference when cloning sockets") Cc: stable@vger.kernel.org # v4.5+ Cc: Johannes Weiner Reported-by: Chris Mason Signed-off-by: Tejun Heo --- kernel/cgroup/cgroup.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-) diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index b1cc1c306668..10951d5e35d2 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -437,6 +437,11 @@ out_unlock: } static void cgroup_get(struct cgroup *cgrp) +{ + css_get(&cgrp->self); +} + +static void cgroup_get_live(struct cgroup *cgrp) { WARN_ON_ONCE(cgroup_is_dead(cgrp)); css_get(&cgrp->self); @@ -932,7 +937,7 @@ static void link_css_set(struct list_head *tmp_links, struct css_set *cset, list_add_tail(&link->cgrp_link, &cset->cgrp_links); if (cgroup_parent(cgrp)) - cgroup_get(cgrp); + cgroup_get_live(cgrp); } /** @@ -1802,7 +1807,7 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type, return ERR_PTR(-EINVAL); } cgrp_dfl_visible = true; - cgroup_get(&cgrp_dfl_root.cgrp); + cgroup_get_live(&cgrp_dfl_root.cgrp); dentry = cgroup_do_mount(&cgroup2_fs_type, flags, &cgrp_dfl_root, CGROUP2_SUPER_MAGIC, ns); @@ -2575,7 +2580,7 @@ restart: if (!css || !percpu_ref_is_dying(&css->refcnt)) continue; - cgroup_get(dsct); + cgroup_get_live(dsct); prepare_to_wait(&dsct->offline_waitq, &wait, TASK_UNINTERRUPTIBLE); @@ -3946,7 +3951,7 @@ static void init_and_link_css(struct cgroup_subsys_state *css, { lockdep_assert_held(&cgroup_mutex); - cgroup_get(cgrp); + cgroup_get_live(cgrp); memset(css, 0, sizeof(*css)); css->cgroup = cgrp; @@ -4122,7 +4127,7 @@ static struct cgroup *cgroup_create(struct cgroup *parent) /* allocation complete, commit to creation */ list_add_tail_rcu(&cgrp->self.sibling, &cgroup_parent(cgrp)->self.children); atomic_inc(&root->nr_cgrps); - cgroup_get(parent); + cgroup_get_live(parent); /* * @cgrp is now fully operational. If something fails after this @@ -4946,7 +4951,7 @@ struct cgroup *cgroup_get_from_path(const char *path) if (kn) { if (kernfs_type(kn) == KERNFS_DIR) { cgrp = kn->priv; - cgroup_get(cgrp); + cgroup_get_live(cgrp); } else { cgrp = ERR_PTR(-ENOTDIR); } @@ -5026,6 +5031,11 @@ void cgroup_sk_alloc(struct sock_cgroup_data *skcd) /* Socket clone path */ if (skcd->val) { + /* + * We might be cloning a socket which is left in an empty + * cgroup and the cgroup might have already been rmdir'd. + * Don't use cgroup_get_live(). + */ cgroup_get(sock_cgroup_ptr(skcd)); return; }