Messages in this thread Patch in this message | | | From | Jiri Slaby <> | Subject | [PATCH 3.12 75/76] sched: Remove lockdep check in sched_move_task() | Date | Thu, 19 May 2016 11:08:37 +0200 |
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From: Kirill Tkhai <ktkhai@parallels.com>
3.12-stable review patch. If anyone has any objections, please let me know.
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commit f7b8a47da17c9ee4998f2ca2018fcc424e953c0e upstream.
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: eeb61e53ea19 ("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> Signed-off-by: Jiri Slaby <jslaby@suse.cz> --- kernel/sched/core.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index dd794a9b6850..e382c14652d0 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6865,8 +6865,12 @@ void sched_move_task(struct task_struct *tsk) if (unlikely(running)) tsk->sched_class->put_prev_task(rq, tsk); - tg = container_of(task_css_check(tsk, cpu_cgroup_subsys_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_cgroup_subsys_id, true), struct task_group, css); tg = autogroup_task_group(tsk, tg); tsk->sched_task_group = tg; -- 2.8.2
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