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Commit 8b08ca52 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

rcu: Fix RCU lockdep splat in set_task_cpu on fork path 



Add an RCU read-side critical section to suppress this false
positive.

Located-by: default avatarEric Paris <eparis@parisplace.org>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
Cc: eric.dumazet@gmail.com
LKML-Reference: <1271880131-3951-1-git-send-email-paulmck@linux.vnet.ibm.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 4b402210

kernel/sched.c

+10 −0
Original line number Diff line number Diff line
@@ -323,6 +323,15 @@ static inline struct task_group *task_group(struct task_struct *p) 
/* Change a task's cfs_rq and parent entity if it moves across CPUs/groups */

static inline void set_task_rq(struct task_struct *p, unsigned int cpu)

{

	/*

	 * Strictly speaking this rcu_read_lock() is not needed since the

	 * task_group is tied to the cgroup, which in turn can never go away

	 * as long as there are tasks attached to it.

	 *

	 * However since task_group() uses task_subsys_state() which is an

	 * rcu_dereference() user, this quiets CONFIG_PROVE_RCU.

	 */

	rcu_read_lock();

#ifdef CONFIG_FAIR_GROUP_SCHED

	p->se.cfs_rq = task_group(p)->cfs_rq[cpu];

	p->se.parent = task_group(p)->se[cpu];
@@ -332,6 +341,7 @@ static inline void set_task_rq(struct task_struct *p, unsigned int cpu) 
	p->rt.rt_rq  = task_group(p)->rt_rq[cpu];

	p->rt.parent = task_group(p)->rt_se[cpu];

#endif

	rcu_read_unlock();

}



#else