Commit f7b8a47d authored Oct 28, 2014 by Kirill Tkhai Committed by Ingo Molnar Nov 04, 2014

sched: Remove lockdep check in sched_move_task()



sched_move_task() is the only interface to change sched_task_group:
cpu_cgrp_subsys methods and autogroup_move_group() use it.

Everything is synchronized by task_rq_lock(), so cpu_cgroup_attach()
is ordered with other users of sched_move_task(). This means we do no
need RCU here: if we've dereferenced a tg here, the .attach method
hasn't been called for it yet.

Thus, we should pass "true" to task_css_check() to silence lockdep
warnings.

Fixes: eeb61e53 ("sched: Fix race between task_group and sched_task_group")
Reported-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1414473874.8574.2.camel@tkhai


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 980d0d51

kernel/sched/core.c

+6 −2

Original line number	Original line	Diff line number	Diff line
	@@ -7444,8 +7444,12 @@ void sched_move_task(struct task_struct *tsk)
	if (unlikely(running))		if (unlikely(running))
	put_prev_task(rq, tsk);		put_prev_task(rq, tsk);

	tg = container_of(task_css_check(tsk, cpu_cgrp_id,		/*
	lockdep_is_held(&tsk->sighand->siglock)),		* All callers are synchronized by task_rq_lock(); we do not use RCU
			* which is pointless here. Thus, we pass "true" to task_css_check()
			* to prevent lockdep warnings.
			*/
			tg = container_of(task_css_check(tsk, cpu_cgrp_id, true),
	struct task_group, css);		struct task_group, css);
	tg = autogroup_task_group(tsk, tg);		tg = autogroup_task_group(tsk, tg);
	tsk->sched_task_group = tg;		tsk->sched_task_group = tg;

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