[PATCH 2/2] srcu: Remove needless updating of srcu_have_cbs in srcu_gp_end()

[Pingfan Liu <kernelfans@gmail.com>]

At present, snp->srcu_have_cbs[idx] is updated by either
srcu_funnel_gp_start() or srcu_gp_end().

But as the code changes, now, srcu_funnel_gp_start() is called with srcu
read lock held. And its input parameter s, s = rcu_seq_snap(&ssp->srcu_gp_seq),
whose counter field always proceeds that of the srcu_gp_seq by one or two.

If the seq snap only proceeds by one, the state machine should be in
state SRCU_STATE_IDLE, the held srcu read lock will prevent the state
machine from moving ahead. So when srcu_gp_end() updates
snp->srcu_have_cbs[idx], the idx must be the past idx for
srcu_funnel_gp_start() that is cared by nobody.

So removing the unnecessary updating in srcu_gp_end().

Test info:
  Running "tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration 10h --configs 18*SRCU-P"
without any failure.

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>
To: rcu@vger.kernel.org
---
 kernel/rcu/srcutree.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 7df59fc8073e..c54d6c04751f 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -783,8 +783,6 @@ static void srcu_gp_end(struct srcu_struct *ssp)
 			last_lvl = snp >= ssp->level[rcu_num_lvls - 1];
 			if (last_lvl)
 				cbs = ss_state < SRCU_SIZE_BIG || snp->srcu_have_cbs[idx] == gpseq;
-			snp->srcu_have_cbs[idx] = gpseq;
-			rcu_seq_set_state(&snp->srcu_have_cbs[idx], 1);
 			sgsne = snp->srcu_gp_seq_needed_exp;
 			if (srcu_invl_snp_seq(sgsne) || ULONG_CMP_LT(sgsne, gpseq))
 				WRITE_ONCE(snp->srcu_gp_seq_needed_exp, gpseq);
-- 
2.31.1