648bb56d07 ("cgroup: lock cgroup_mutex in cgroup_init_subsys()") made
cgroup_init_subsys() grab cgroup_mutex before invoking ->css_alloc()
for the root css. Because memcg registers hotcpu notifier from
->css_alloc() for the root css, this introduced circular locking
dependency between cgroup_mutex and cpu hotplug.
Fix it by moving hotcpu notifier registration to a subsys initcall.
======================================================
[ INFO: possible circular locking dependency detected ]
3.7.0-rc4-work+ #42 Not tainted
-------------------------------------------------------
bash/645 is trying to acquire lock:
(cgroup_mutex){+.+.+.}, at: [<ffffffff8110c5b7>] cgroup_lock+0x17/0x20
but task is already holding lock:
(cpu_hotplug.lock){+.+.+.}, at: [<ffffffff8109300f>] cpu_hotplug_begin+0x2f/0x60
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (cpu_hotplug.lock){+.+.+.}:
[<ffffffff810f8357>] lock_acquire+0x97/0x1e0
[<ffffffff81be4701>] mutex_lock_nested+0x61/0x3b0
[<ffffffff810930fc>] get_online_cpus+0x3c/0x60
[<ffffffff811152fb>] rebuild_sched_domains_locked+0x1b/0x70
[<ffffffff81116718>] cpuset_write_resmask+0x298/0x2c0
[<ffffffff8110f70f>] cgroup_file_write+0x1ef/0x300
[<ffffffff811c3b78>] vfs_write+0xa8/0x160
[<ffffffff811c3e82>] sys_write+0x52/0xa0
[<ffffffff81be89c2>] system_call_fastpath+0x16/0x1b
-> #0 (cgroup_mutex){+.+.+.}:
[<ffffffff810f74de>] __lock_acquire+0x14ce/0x1d20
[<ffffffff810f8357>] lock_acquire+0x97/0x1e0
[<ffffffff81be4701>] mutex_lock_nested+0x61/0x3b0
[<ffffffff8110c5b7>] cgroup_lock+0x17/0x20
[<ffffffff81116deb>] cpuset_handle_hotplug+0x1b/0x560
[<ffffffff8111744e>] cpuset_update_active_cpus+0xe/0x10
[<ffffffff810d0587>] cpuset_cpu_inactive+0x47/0x50
[<ffffffff810c1476>] notifier_call_chain+0x66/0x150
[<ffffffff810c156e>] __raw_notifier_call_chain+0xe/0x10
[<ffffffff81092fa0>] __cpu_notify+0x20/0x40
[<ffffffff81b9827e>] _cpu_down+0x7e/0x2f0
[<ffffffff81b98526>] cpu_down+0x36/0x50
[<ffffffff81b9c12d>] store_online+0x5d/0xe0
[<ffffffff816b6ef8>] dev_attr_store+0x18/0x30
[<ffffffff8123bb50>] sysfs_write_file+0xe0/0x150
[<ffffffff811c3b78>] vfs_write+0xa8/0x160
[<ffffffff811c3e82>] sys_write+0x52/0xa0
[<ffffffff81be89c2>] system_call_fastpath+0x16/0x1b
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(cpu_hotplug.lock);
lock(cgroup_mutex);
lock(cpu_hotplug.lock);
lock(cgroup_mutex);
*** DEADLOCK ***
5 locks held by bash/645:
#0: (&buffer->mutex){+.+.+.}, at: [<ffffffff8123bab8>] sysfs_write_file+0x48/0x150
#1: (s_active#42){.+.+.+}, at: [<ffffffff8123bb38>] sysfs_write_file+0xc8/0x150
#2: (x86_cpu_hotplug_driver_mutex){+.+...}, at: [<ffffffff81079277>] cpu_hotplug_driver_lock+0x1
+7/0x20
#3: (cpu_add_remove_lock){+.+.+.}, at: [<ffffffff81093157>] cpu_maps_update_begin+0x17/0x20
#4: (cpu_hotplug.lock){+.+.+.}, at: [<ffffffff8109300f>] cpu_hotplug_begin+0x2f/0x60
stack backtrace:
Pid: 645, comm: bash Not tainted 3.7.0-rc4-work+ #42
Call Trace:
[<ffffffff81bdadfd>] print_circular_bug+0x28e/0x29f
[<ffffffff810f74de>] __lock_acquire+0x14ce/0x1d20
[<ffffffff810f8357>] lock_acquire+0x97/0x1e0
[<ffffffff81be4701>] mutex_lock_nested+0x61/0x3b0
[<ffffffff8110c5b7>] cgroup_lock+0x17/0x20
[<ffffffff81116deb>] cpuset_handle_hotplug+0x1b/0x560
[<ffffffff8111744e>] cpuset_update_active_cpus+0xe/0x10
[<ffffffff810d0587>] cpuset_cpu_inactive+0x47/0x50
[<ffffffff810c1476>] notifier_call_chain+0x66/0x150
[<ffffffff810c156e>] __raw_notifier_call_chain+0xe/0x10
[<ffffffff81092fa0>] __cpu_notify+0x20/0x40
[<ffffffff81b9827e>] _cpu_down+0x7e/0x2f0
[<ffffffff81b98526>] cpu_down+0x36/0x50
[<ffffffff81b9c12d>] store_online+0x5d/0xe0
[<ffffffff816b6ef8>] dev_attr_store+0x18/0x30
[<ffffffff8123bb50>] sysfs_write_file+0xe0/0x150
[<ffffffff811c3b78>] vfs_write+0xa8/0x160
[<ffffffff811c3e82>] sys_write+0x52/0xa0
[<ffffffff81be89c2>] system_call_fastpath+0x16/0x1b
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Reported-by: Fengguang Wu <fengguang.wu@xxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
---
Michal, if it looks okay, can you please route this patch?
Thanks.
mm/memcontrol.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 12307b3..7d8a27f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4982,7 +4982,6 @@ mem_cgroup_css_alloc(struct cgroup *cont)
&per_cpu(memcg_stock, cpu);
INIT_WORK(&stock->work, drain_local_stock);
}
- hotcpu_notifier(memcg_cpu_hotplug_callback, 0);
} else {
parent = mem_cgroup_from_cont(cont->parent);
memcg->use_hierarchy = parent->use_hierarchy;
@@ -5644,6 +5643,19 @@ struct cgroup_subsys mem_cgroup_subsys = {
.use_id = 1,
};
+/*
+ * The rest of init is performed during ->css_alloc() for root css which
+ * happens before initcalls. hotcpu_notifier() can't be done together as
+ * it would introduce circular locking by adding cgroup_lock -> cpu hotplug
+ * dependency. Do it from a subsys_initcall().
+ */
+static int __init mem_cgroup_init(void)
+{
+ hotcpu_notifier(memcg_cpu_hotplug_callback, 0);
+ return 0;
+}
+subsys_initcall(mem_cgroup_init);
+
#ifdef CONFIG_MEMCG_SWAP
static int __init enable_swap_account(char *s)
{
--
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