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authorSebastian Andrzej Siewior <bigeasy@linutronix.de>2022-03-23 16:06:29 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2022-03-23 19:00:34 -0700
commitb1e2c8df0f007f34c373925471c7b493c9e16620 (patch)
treefbad1a9fc23197afca9fd14ea9130367b798a2fa /kernel
parent2cd50532ce5c798c029a39234ad7f48a174e15ec (diff)
downloadlinux-b1e2c8df0f007f34c373925471c7b493c9e16620.tar.bz2
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 cgroup_rstat_flush_locked(). 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. Link: https://lkml.kernel.org/r/20220301122143.1521823-2-bigeasy@linutronix.de Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Acked-by: Tejun Heo <tj@kernel.org> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Zefan Li <lizefan.x@bytedance.com> From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Subject: cgroup: add a comment to cgroup_rstat_flush_locked(). Add a comment why spin_lock_irq() -> raw_spin_lock_irqsave() is needed. Link: https://lkml.kernel.org/r/Yh+DOK73hfVV5ThX@linutronix.de Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Acked-by: Tejun Heo <tj@kernel.org> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Zefan Li <lizefan.x@bytedance.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/cgroup/rstat.c13
1 files changed, 11 insertions, 2 deletions
diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
index 9d331ba44870..ba7a660184e4 100644
--- a/kernel/cgroup/rstat.c
+++ b/kernel/cgroup/rstat.c
@@ -153,8 +153,17 @@ static void cgroup_rstat_flush_locked(struct cgroup *cgrp, bool may_sleep)
raw_spinlock_t *cpu_lock = per_cpu_ptr(&cgroup_rstat_cpu_lock,
cpu);
struct cgroup *pos = NULL;
+ unsigned long flags;
- raw_spin_lock(cpu_lock);
+ /*
+ * The _irqsave() is needed because cgroup_rstat_lock is
+ * spinlock_t which is a sleeping lock on PREEMPT_RT. Acquiring
+ * this lock with the _irq() suffix only disables interrupts on
+ * a non-PREEMPT_RT kernel. The raw_spinlock_t below disables
+ * interrupts on both configurations. The _irqsave() ensures
+ * that interrupts are always disabled and later restored.
+ */
+ raw_spin_lock_irqsave(cpu_lock, flags);
while ((pos = cgroup_rstat_cpu_pop_updated(pos, cgrp, cpu))) {
struct cgroup_subsys_state *css;
@@ -166,7 +175,7 @@ static void cgroup_rstat_flush_locked(struct cgroup *cgrp, bool may_sleep)
css->ss->css_rstat_flush(css, cpu);
rcu_read_unlock();
}
- 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() ||