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cgroup: use irqsave in cgroup_rstat_flush_locked().

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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>
This commit is contained in:
Sebastian Andrzej Siewior 2022-03-23 16:06:29 -07:00 committed by Linus Torvalds
parent 2cd50532ce
commit b1e2c8df0f
1 changed files with 11 additions and 2 deletions
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13
kernel/cgroup/rstat.c
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@ -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() ||