I see this was just applied to Linus's tree. This too probably should be tagged for stable as well.
-- Steve On Tue, 6 Feb 2018 03:54:42 -0800 "tip-bot for Steven Rostedt (VMware)" <tip...@zytor.com> wrote: > Commit-ID: 364f56653708ba8bcdefd4f0da2a42904baa8eeb > Gitweb: > https://git.kernel.org/tip/364f56653708ba8bcdefd4f0da2a42904baa8eeb > Author: Steven Rostedt (VMware) <rost...@goodmis.org> > AuthorDate: Tue, 23 Jan 2018 20:45:38 -0500 > Committer: Ingo Molnar <mi...@kernel.org> > CommitDate: Tue, 6 Feb 2018 10:20:33 +0100 > > sched/rt: Up the root domain ref count when passing it around via IPIs > > 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 <pkond...@codeaurora.org> > Signed-off-by: Steven Rostedt (VMware) <rost...@goodmis.org> > Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> > Cc: Andrew Morton <a...@linux-foundation.org> > Cc: Linus Torvalds <torva...@linux-foundation.org> > Cc: Mike Galbraith <efa...@gmx.de> > Cc: Peter Zijlstra <pet...@infradead.org> > Cc: Thomas Gleixner <t...@linutronix.de> > Fixes: 4bdced5c9a292 ("sched/rt: Simplify the IPI based RT balancing logic") > Link: > http://lkml.kernel.org/r/CAEU1=pkiho35dzna8eqqnskw1fr1y1zrq5y66x117mg06sq...@mail.gmail.com > Signed-off-by: Ingo Molnar <mi...@kernel.org> > --- > kernel/sched/rt.c | 9 +++++++-- > kernel/sched/sched.h | 2 ++ > kernel/sched/topology.c | 13 +++++++++++++ > 3 files changed, 22 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c > index 2fb627d..89a086e 100644 > --- a/kernel/sched/rt.c > +++ b/kernel/sched/rt.c > @@ -1990,8 +1990,11 @@ 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 */ > @@ -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); > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index 2e95505..fb5fc45 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -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); > diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c > index 034cbed..519b024 100644 > --- a/kernel/sched/topology.c > +++ b/kernel/sched/topology.c > @@ -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))
