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 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
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-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 364f56653708ba8bcdefd4f0da2a42904baa8eeb Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
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@xxxxxxxxxxx>
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@xxxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Fixes: 4bdced5c9a292 ("sched/rt: Simplify the IPI based RT balancing logic")
Link: http://lkml.kernel.org/r/CAEU1=PkiHO35Dzna8EQqNSKW1fr1y1zRQ5y66X117MG06sQtNA@xxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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
@@ -5896,6 +5896,19 @@ 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
@@ -1916,8 +1916,11 @@ 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 */
@@ -1947,8 +1950,10 @@ 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
@@ -553,6 +553,8 @@ 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@xxxxxxxxxxx are
queue-4.4/sched-rt-use-container_of-to-get-root-domain-in-rto_push_irq_work_func.patch
queue-4.4/sched-rt-up-the-root-domain-ref-count-when-passing-it-around-via-ipis.patch