From c350705d725b07cd92ee77500fdb5b10cd4990a0 Mon Sep 17 00:00:00 2001
From: Sebastian Andrzej Siewior <>
Date: Tue, 3 Jul 2018 18:19:48 +0200
Subject: [PATCH 073/166] cgroup: use irqsave in cgroup_rstat_flush_locked()

All callers of cgroup_rstat_flush_locked() acquire cgroup_rstat_lock
either with spin_lock_irq() or spin_lock_irqsave().
cgroup_rstat_flush_locked() itself acquires cgroup_rstat_cpu_lock which
is a raw_spin_lock. This lock is also acquired in cgroup_rstat_updated()
in IRQ context and therefore requires _irqsave() locking suffix in
Since there is no difference between spin_lock_t and raw_spin_lock_t
on !RT lockdep does not complain here. On RT lockdep complains because
the interrupts were not disabled here and a deadlock is possible.

Acquire the raw_spin_lock_t with disabled interrupts.

Signed-off-by: Sebastian Andrzej Siewior <>
Signed-off-by: Thomas Gleixner <>
 kernel/cgroup/rstat.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

Index: linux-5.15.32-rt39/kernel/cgroup/rstat.c
@ linux-5.15.32-rt39/kernel/cgroup/rstat.c:159 @ static void cgroup_rstat_flush_locked(st
 		raw_spinlock_t *cpu_lock = per_cpu_ptr(&cgroup_rstat_cpu_lock,
 		struct cgroup *pos = NULL;
+		unsigned long flags;
-		raw_spin_lock(cpu_lock);
+		raw_spin_lock_irqsave(cpu_lock, flags);
 		while ((pos = cgroup_rstat_cpu_pop_updated(pos, cgrp, cpu))) {
 			struct cgroup_subsys_state *css;
@ linux-5.15.32-rt39/kernel/cgroup/rstat.c:173 @ static void cgroup_rstat_flush_locked(st
 				css->ss->css_rstat_flush(css, cpu);
-		raw_spin_unlock(cpu_lock);
+		raw_spin_unlock_irqrestore(cpu_lock, flags);
 		/* if @may_sleep, play nice and yield if necessary */
 		if (may_sleep && (need_resched() ||