This is a note to let you know that I've just added the patch titled

sched/rt: Up the root domain ref count when passing it around via IPIs

to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: sched-rt-up-the-root-domain-ref-count-when-passing-it-around-via-ipis.patch and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 364f56653708ba8bcdefd4f0da2a42904baa8eeb Mon Sep 17 00:00:00 2001

From: "Steven Rostedt (VMware)" rostedt@goodmis.org Date: Tue, 23 Jan 2018 20:45:38 -0500 Subject: sched/rt: Up the root domain ref count when passing it around via IPIs

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);

Patches currently in stable-queue which might be from rostedt@goodmis.org are

queue-4.9/sched-rt-use-container_of-to-get-root-domain-in-rto_push_irq_work_func.patch queue-4.9/sched-rt-up-the-root-domain-ref-count-when-passing-it-around-via-ipis.patch