[PATCH 1/3] srcu: Eliminate the requirement of SRCU_SIZE_WAIT_CALL

[Pingfan Liu <kernelfans@gmail.com>]

The state SRCU_SIZE_WAIT_CALL is only used in srcu_gp_start_if_needed().
And it is not needed. Because counter_wrap_check has guarantee that both
srcu_gp_seq_needed and srcu_gp_seq_needed_exp are not far behind
srcu_gp_seq and no false alarm will be raised by the statement in
srcu_gp_start_if_needed()

  ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)

As a result, once if SRCU_SIZE_WAIT_BARRIER is seen, the tree snp can be
used immediately, not need to wait for another srcu_gp_end() to update
the srcu_gp_seq_needed and srcu_gp_seq_needed_exp to avoid false alarm.

Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: "Zhang, Qiang1" <qiang1.zhang@intel.com>
To: rcu@vger.kernel.org
---
 kernel/rcu/srcutree.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 1c304fec89c0..fe0759d89c2d 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -1092,7 +1092,7 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
 	check_init_srcu_struct(ssp);
 	idx = srcu_read_lock(ssp);
 	ss_state = smp_load_acquire(&ssp->srcu_size_state);
-	if (ss_state < SRCU_SIZE_WAIT_CALL)
+	if (ss_state < SRCU_SIZE_WAIT_BARRIER)
 		sdp = per_cpu_ptr(ssp->sda, 0);
 	else
 		sdp = raw_cpu_ptr(ssp->sda);
-- 
2.31.1