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cgroup: css_set_lock should nest inside tasklist_lock

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cgroup_enable_task_cg_lists() incorrectly nests non-irq-safe
tasklist_lock inside irq-safe css_set_lock triggering the following
lockdep warning.

  WARNING: possible irq lock inversion dependency detected
  4.17.0-rc1-00027-gb37d049 #6 Not tainted
  --------------------------------------------------------
  systemd/1 just changed the state of lock:
  00000000fe57773b (css_set_lock){..-.}, at: cgroup_free+0xf2/0x12a
  but this lock took another, SOFTIRQ-unsafe lock in the past:
   (tasklist_lock){.+.+}

  and interrupts could create inverse lock ordering between them.

  other info that might help us debug this:
   Possible interrupt unsafe locking scenario:

	 CPU0                    CPU1
	 ----                    ----
    lock(tasklist_lock);
				 local_irq_disable();
				 lock(css_set_lock);
				 lock(tasklist_lock);
    <Interrupt>
      lock(css_set_lock);

   *** DEADLOCK ***

The condition is highly unlikely to actually happen especially given
that the path is executed only once per boot.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Boqun Feng <boqun.feng@gmail.com>
This commit is contained in:
Tejun Heo 2018-05-23 11:04:54 -07:00
parent cc659e76f3
commit d8742e2290
1 changed files with 8 additions and 8 deletions
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16
kernel/cgroup/cgroup.c
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@ -1798,13 +1798,6 @@ static void cgroup_enable_task_cg_lists(void)
{
struct task_struct *p, *g;
spin_lock_irq(&css_set_lock);
if (use_task_css_set_links)
goto out_unlock;
use_task_css_set_links = true;
/*
* We need tasklist_lock because RCU is not safe against
* while_each_thread(). Besides, a forking task that has passed
@ -1813,6 +1806,13 @@ static void cgroup_enable_task_cg_lists(void)
* tasklist if we walk through it with RCU.
*/
read_lock(&tasklist_lock);
spin_lock_irq(&css_set_lock);
if (use_task_css_set_links)
goto out_unlock;
use_task_css_set_links = true;
do_each_thread(g, p) {
WARN_ON_ONCE(!list_empty(&p->cg_list) ||
task_css_set(p) != &init_css_set);
@ -1840,9 +1840,9 @@ static void cgroup_enable_task_cg_lists(void)
}
spin_unlock(&p->sighand->siglock);
} while_each_thread(g, p);
read_unlock(&tasklist_lock);
out_unlock:
spin_unlock_irq(&css_set_lock);
read_unlock(&tasklist_lock);
}
static void init_cgroup_housekeeping(struct cgroup *cgrp)