Messages in this thread Patch in this message | | | From | "Xu, Yanfei" <> | Subject | [Qestion] Is preempt_disable/enable needed in non-preemption code path | Date | Thu, 15 Apr 2021 23:04:05 +0800 |
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Hi experts,
I am learning rcu mechanism and its codes. When looking at the rcu_blocking_is_gp(), I found there is a pair preemption disable/enable operation in non-preemption code path. And it has been a long time. I can't understand why we need it? Is there some thing I missed? If not, can we remove the unnecessary operation like blow?
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index da6f5213fb74..c6d95a00715e 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3703,7 +3703,6 @@ static int rcu_blocking_is_gp(void) if (IS_ENABLED(CONFIG_PREEMPTION)) return rcu_scheduler_active == RCU_SCHEDULER_INACTIVE; might_sleep(); /* Check for RCU read-side critical section. */ - preempt_disable(); /* * If the rcu_state.n_online_cpus counter is equal to one, * there is only one CPU, and that CPU sees all prior accesses @@ -3718,7 +3717,6 @@ static int rcu_blocking_is_gp(void) * Those memory barriers are provided by CPU-hotplug code. */ ret = READ_ONCE(rcu_state.n_online_cpus) <= 1; - preempt_enable(); return ret; }
Best regards, Yanfei
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