On 2019/10/31 11:07 下午, Paul E. McKenney wrote:
On Thu, Oct 31, 2019 at 10:35:22PM +0800, Lai Jiangshan wrote:
On 2019/10/31 10:10 下午, Paul E. McKenney wrote:
On Thu, Oct 31, 2019 at 10:07:59AM +0000, Lai Jiangshan wrote:
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.
Hmmm... Testing identified the need for this one. But I will wait for
your responses on the earlier patches before going any further through
this series.
Hmmm... I was wrong, it should be after patch7 to avoid
the scheduler deadlock.
I was wondering about that. ;-)
This patch was split from the core patch(patch8: don't use negative
->rcu_read_lock_nesting).
When I reordered "fixing something" as patch1/2, I reordered
it close to the patch of clean up rcu_preempt_deferred_qs_irqrestore
caused this mistake.
I will reorder it back later and "fixing something" is fixing
nothing and I will drop patch 1/2. Could you continue to review
further through this series please? Sorry for any mistakes.
Thanks
Lai
Thanx, Paul
Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
---
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
