Commit a3e72739 authored Sep 25, 2015 by Tejun Heo

cgroup: fix too early usage of static_branch_disable()



49d1dc4b ("cgroup: implement static_key based
cgroup_subsys_enabled() and cgroup_subsys_on_dfl()") converted cgroup
enabled test to use static_key; however, cgroup_disable() is called
before static_key subsystem itself is initialized and thus leads to
the following warning when "cgroup_disable=" parameter is specified.

 WARNING: CPU: 0 PID: 0 at kernel/jump_label.c:99 static_key_slow_dec+0x44/0x60()
 static_key_slow_dec used before call to jump_label_init
 ...
 Call Trace:
  [<ffffffff813b18c2>] dump_stack+0x44/0x62
  [<ffffffff8108dd52>] warn_slowpath_common+0x82/0xc0
  [<ffffffff8108ddec>] warn_slowpath_fmt+0x5c/0x80
  [<ffffffff8119c054>] static_key_slow_dec+0x44/0x60
  [<ffffffff81d826b6>] cgroup_disable+0xaf/0xd6
  [<ffffffff81d5f9de>] unknown_bootoption+0x8c/0x194
  [<ffffffff810b0c03>] parse_args+0x273/0x4a0
  [<ffffffff81d5fd67>] start_kernel+0x205/0x4b8
 ...

Fix it by making cgroup_disable() to record the subsystems to disable
in cgroup_disable_mask and moving the actual application to
cgroup_init() which is late enough and where the enabled state is
first used.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Andrey Wagin <avagin@gmail.com>
Link: http://lkml.kernel.org/g/CANaxB-yFuS4SA2znSvcKrO9L_CbHciHYW+o9bN8sZJ8eR9FxYA@mail.gmail.com
Fixes: 49d1dc4b

parent c0522908

kernel/cgroup.c

+8 −6

Original line number	Diff line number	Diff line
		@@ -5124,6 +5124,8 @@ int __init cgroup_init_early(void)
		return 0;
		}

		static unsigned long cgroup_disable_mask __initdata;

		/**
		* cgroup_init - cgroup initialization
		*
		@@ -5170,8 +5172,12 @@ int __init cgroup_init(void)
		* disabled flag and cftype registration needs kmalloc,
		* both of which aren't available during early_init.
		*/
		if (!cgroup_ssid_enabled(ssid))
		if (cgroup_disable_mask & (1 << ssid)) {
		static_branch_disable(cgroup_subsys_enabled_key[ssid]);
		printk(KERN_INFO "Disabling %s control group subsystem\n",
		ss->name);
		continue;
		}

		cgrp_dfl_root.subsys_mask \|= 1 << ss->id;

		@@ -5595,11 +5601,7 @@ static int __init cgroup_disable(char *str)
		if (strcmp(token, ss->name) &&
		strcmp(token, ss->legacy_name))
		continue;

		static_branch_disable(cgroup_subsys_enabled_key[i]);
		printk(KERN_INFO "Disabling %s control group subsystem\n",
		ss->name);
		break;
		cgroup_disable_mask \|= 1 << i;
		}
		}
		return 1;

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