Re: [Linux-stable-mirror] [tip:sched/urgent] sched/rt: Use container_of() to get root domain in rto_push_irq_work_func()

I see this was just applied to Linus's tree. It probably should be tagged for stable as well.

-- Steve

On Tue, 6 Feb 2018 03:54:16 -0800 "tip-bot for Steven Rostedt (VMware)" tipbot@zytor.com wrote:

Commit-ID: ad0f1d9d65938aec72a698116cd73a980916895e Gitweb: https://git.kernel.org/tip/ad0f1d9d65938aec72a698116cd73a980916895e Author: Steven Rostedt (VMware) rostedt@goodmis.org AuthorDate: Tue, 23 Jan 2018 20:45:37 -0500 Committer: Ingo Molnar mingo@kernel.org CommitDate: Tue, 6 Feb 2018 10:20:33 +0100

sched/rt: Use container_of() to get root domain in rto_push_irq_work_func()

When the rto_push_irq_work_func() is called, it looks at the RT overloaded bitmask in the root domain via the runqueue (rq->rd). The problem is that during CPU up and down, nothing here stops rq->rd from changing between taking the rq->rd->rto_lock and releasing it. That means the lock that is released is not the same lock that was taken.

Instead of using this_rq()->rd to get the root domain, as the irq work is part of the root domain, we can simply get the root domain from the irq work that is passed to the routine:

container_of(work, struct root_domain, rto_push_work)

This keeps the root domain consistent.

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

---

kernel/sched/rt.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 862a513..2fb627d 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1907,9 +1907,8 @@ static void push_rt_tasks(struct rq *rq)

• the rt_loop_next will cause the iterator to perform another scan.

*/ -static int rto_next_cpu(struct rq *rq) +static int rto_next_cpu(struct root_domain *rd) {

• struct root_domain *rd = rq->rd; int next; int cpu;

@@ -1985,7 +1984,7 @@ static void tell_cpu_to_push(struct rq *rq) * Otherwise it is finishing up and an ipi needs to be sent. */ if (rq->rd->rto_cpu < 0)

• cpu = rto_next_cpu(rq);
  

• cpu = rto_next_cpu(rq->rd);
  

raw_spin_unlock(&rq->rd->rto_lock); @@ -1998,6 +1997,8 @@ static void tell_cpu_to_push(struct rq *rq) /* Called from hardirq context */ void rto_push_irq_work_func(struct irq_work *work) {

• struct root_domain *rd =

• container_of(work, struct root_domain, rto_push_work);
  

  struct rq *rq; int cpu;

@@ -2013,18 +2014,18 @@ void rto_push_irq_work_func(struct irq_work *work) raw_spin_unlock(&rq->lock); }

• raw_spin_lock(&rq->rd->rto_lock);

• raw_spin_lock(&rd->rto_lock);

/* Pass the IPI to the next rt overloaded queue */

• cpu = rto_next_cpu(rq);

• cpu = rto_next_cpu(rd);

• raw_spin_unlock(&rq->rd->rto_lock);

• raw_spin_unlock(&rd->rto_lock);

if (cpu < 0) return; /* Try the next RT overloaded CPU */

• irq_work_queue_on(&rq->rd->rto_push_work, cpu);

• irq_work_queue_on(&rd->rto_push_work, cpu);

} #endif /* HAVE_RT_PUSH_IPI */