sched/rt: Up the root domain ref count when passing it around via IPIs (364f5665) · Commits · 戴 / test

When issuing an IPI RT push, where an IPI is sent to each CPU that has more than one RT task scheduled on it, it references the root domain's rto_mask, that contains all the CPUs within the root domain that has more than one RT task in the runable state. The problem is, after the IPIs are initiated, the rq->lock is released. This means that the root domain that is associated to the run queue could be freed while the IPIs are going around. Add a sched_get_rd() and a sched_put_rd() that will increment and decrement the root domain's ref count respectively. This way when initiating the IPIs, the scheduler will up the root domain's ref count before releasing the rq->lock, ensuring that the root domain does not go away until the IPI round is complete. Reported-by:

Pavan Kondeti <pkondeti@codeaurora.org> Signed-off-by:

Steven Rostedt (VMware) <rostedt@goodmis.org> Signed-off-by:

Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Fixes: ("sched/rt: Simplify the IPI based RT balancing logic") Link: http://lkml.kernel.org/r/CAEU1=PkiHO35Dzna8EQqNSKW1fr1y1zRQ5y66X117MG06sQtNA@mail.gmail.com Signed-off-by:

Ingo Molnar <mingo@kernel.org>

kernel/sched/rt.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -1990,9 +1990,12 @@ static void tell_cpu_to_push(struct rq *rq)

		rto_start_unlock(&rq->rd->rto_loop_start);

		if (cpu >= 0)
		if (cpu >= 0) {
		/* Make sure the rd does not get freed while pushing */
		sched_get_rd(rq->rd);
		irq_work_queue_on(&rq->rd->rto_push_work, cpu);
		}
		}

		/* Called from hardirq context */
		void rto_push_irq_work_func(struct irq_work *work)
		@@ -2021,8 +2024,10 @@ void rto_push_irq_work_func(struct irq_work *work)

		raw_spin_unlock(&rd->rto_lock);

		if (cpu < 0)
		if (cpu < 0) {
		sched_put_rd(rd);
		return;
		}

		/* Try the next RT overloaded CPU */
		irq_work_queue_on(&rd->rto_push_work, cpu);

kernel/sched/sched.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -691,6 +691,8 @@ extern struct mutex sched_domains_mutex;
		extern void init_defrootdomain(void);
		extern int sched_init_domains(const struct cpumask *cpu_map);
		extern void rq_attach_root(struct rq rq, struct root_domain rd);
		extern void sched_get_rd(struct root_domain *rd);
		extern void sched_put_rd(struct root_domain *rd);

		#ifdef HAVE_RT_PUSH_IPI
		extern void rto_push_irq_work_func(struct irq_work *work);

kernel/sched/topology.c

+13 −0

Original line number	Diff line number	Diff line
		@@ -259,6 +259,19 @@ void rq_attach_root(struct rq rq, struct root_domain rd)
		call_rcu_sched(&old_rd->rcu, free_rootdomain);
		}

		void sched_get_rd(struct root_domain *rd)
		{
		atomic_inc(&rd->refcount);
		}

		void sched_put_rd(struct root_domain *rd)
		{
		if (!atomic_dec_and_test(&rd->refcount))
		return;

		call_rcu_sched(&rd->rcu, free_rootdomain);
		}

		static int init_rootdomain(struct root_domain *rd)
		{
		if (!zalloc_cpumask_var(&rd->span, GFP_KERNEL))

Admin message