[PATCH 04/11] rcu: cleanup rcu_preempt_deferred_qs()

Lai Jiangshan
2019-10-31T10:08:54Z

Don't need to set ->rcu_read_lock_nesting negative, irq-protected
rcu_preempt_deferred_qs_irqrestore() doesn't expect
->rcu_read_lock_nesting to be negative to work, it even
doesn't access to ->rcu_read_lock_nesting any more.

It is true that NMI over rcu_preempt_deferred_qs_irqrestore()
may access to ->rcu_read_lock_nesting, but it is still safe
since rcu_read_unlock_special() can protect itself from NMI.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
kernel/rcu/tree_plugin.h | 5 -----
1 file changed, 5 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 82595db04eec..9fe8138ed3c3 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -555,16 +555,11 @@ static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
static void rcu_preempt_deferred_qs(struct task_struct *t)
{
unsigned long flags;
- bool couldrecurse = t->rcu_read_lock_nesting >= 0;

if (!rcu_preempt_need_deferred_qs(t))
return;
- if (couldrecurse)
- t->rcu_read_lock_nesting -= RCU_NEST_BIAS;
local_irq_save(flags);
rcu_preempt_deferred_qs_irqrestore(t, flags);
- if (couldrecurse)
- t->rcu_read_lock_nesting += RCU_NEST_BIAS;
}

/*
--
2.20.1