Old srcu implement requires sp->completed is loaded in
RCU-sched(preempt_disable()) section.
The new srcu is now not RCU-sched based, it doesn't require the load of
sp->completed and the access to counter must be in the same RCU-sched
read site C.S., so we use ACCESS_ONCE() instead, and move it out of
the preempt_disable() section, preempt_disable() section is only used
for percpu data, not for RCU-sched.
The resulted code is almost as the same as before, but it helps people to
understand the code, and it avoids to add surprise to reviewer: "why we need
rcu_read_lock_sched_held() here?"
Signed-off-by: Lai Jiangshan <la...@cn.fujitsu.com>
---
kernel/srcu.c | 3 +--
1 files changed, 1 insertions(+), 2 deletions(-)
diff --git a/kernel/srcu.c b/kernel/srcu.c
index 38a762f..224400a 100644
--- a/kernel/srcu.c
+++ b/kernel/srcu.c
@@ -294,9 +294,8 @@ int __srcu_read_lock(struct srcu_struct *sp)
{
int idx;
+ idx = ACCESS_ONCE(sp->completed) & 0x1;
preempt_disable();
- idx = rcu_dereference_index_check(sp->completed,
- rcu_read_lock_sched_held()) & 0x1;
ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->c[idx]) += 1;
smp_mb(); /* B */ /* Avoid leaking the critical section. */
ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->seq[idx]) += 1;
--
1.7.4.4
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