On Tue 18-12-12 07:40:30, Tejun Heo wrote:
> 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>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
> ---
> Michal, if it looks okay, can you please route this patch?
Andrew, could you pick this one up, please?
> 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);
Hmm, we can move enable_swap_cgroup() and per-cpu memcg_stock
initialization here as well to make the css_alloc a bit cleaner.
mem_cgroup_soft_limit_tree_init with a trivial BUG_ON() on allocation
failure can go there as well.
I will do it.
> + return 0;
> +}
> +subsys_initcall(mem_cgroup_init);
> +
> #ifdef CONFIG_MEMCG_SWAP
> static int __init enable_swap_account(char *s)
> {
> --
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--
Michal Hocko
SUSE Labs
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