4.9-stable review patch. If anyone has any objections, please let me know.
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From: Steven Rostedt (VMware) rostedt@goodmis.org
commit 364f56653708ba8bcdefd4f0da2a42904baa8eeb upstream.
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: 4bdced5c9a292 ("sched/rt: Simplify the IPI based RT balancing logic") Link: http://lkml.kernel.org/r/CAEU1=PkiHO35Dzna8EQqNSKW1fr1y1zRQ5y66X117MG06sQtNA... Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/sched/core.c | 13 +++++++++++++ kernel/sched/rt.c | 9 +++++++-- kernel/sched/sched.h | 2 ++ 3 files changed, 22 insertions(+), 2 deletions(-)
--- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5864,6 +5864,19 @@ static void rq_attach_root(struct rq *rq 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) { memset(rd, 0, sizeof(*rd)); --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1978,8 +1978,11 @@ static void tell_cpu_to_push(struct 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 */ @@ -2009,8 +2012,10 @@ void rto_push_irq_work_func(struct irq_w
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); --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -590,6 +590,8 @@ struct root_domain { };
extern struct root_domain def_root_domain; +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);