| Message ID | 20220301122143.1521823-2-bigeasy@linutronix.de (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [1/2] cgroup: Use irqsave in cgroup_rstat_flush_locked(). | expand |
Hello, On Tue, Mar 01, 2022 at 01:21:42PM +0100, Sebastian Andrzej Siewior wrote: > 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. > > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Can you please add a comment explaining why irqsave is being used? As it stands, it just looks spurious. Thanks.
diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c index 9d331ba44870a..53b771c20ee50 100644 --- a/kernel/cgroup/rstat.c +++ b/kernel/cgroup/rstat.c @@ -153,8 +153,9 @@ 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); + raw_spin_lock_irqsave(cpu_lock, flags); while ((pos = cgroup_rstat_cpu_pop_updated(pos, cgrp, cpu))) { struct cgroup_subsys_state *css; @@ -166,7 +167,7 @@ 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() ||
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. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- kernel/cgroup/rstat.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)