linux-kernel - [PATCH 2/3] srcu: Remove superfluous sdp->srcu_lock

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Date:   Fri,  2 Apr 2021 01:47:03 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     "Paul E . McKenney" <paulmck@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Josh Triplett <josh@...htriplett.org>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: [PATCH 2/3] srcu: Remove superfluous sdp->srcu_lock_count zero filling

alloc_percpu() zeroes out the allocated memory. Therefore we can assume
the whole struct srcu_data to be clear after calling it, just like after
a static initialization. No need for a special treatment in the dynamic
allocation case.

Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Cc: Boqun Feng <boqun.feng@...il.com>
Cc: Lai Jiangshan <jiangshanlai@...il.com>
Cc: Neeraj Upadhyay <neeraju@...eaurora.org>
Cc: Josh Triplett <josh@...htriplett.org>
Cc: Joel Fernandes <joel@...lfernandes.org>
Cc: Uladzislau Rezki <urezki@...il.com>
---
 kernel/rcu/srcutree.c | 12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 7197156418e4..10e681ea7051 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -80,7 +80,7 @@ do {									\
  * srcu_read_unlock() running against them.  So if the is_static parameter
  * is set, don't initialize ->srcu_lock_count[] and ->srcu_unlock_count[].
  */
-static void init_srcu_struct_nodes(struct srcu_struct *ssp, bool is_static)
+static void init_srcu_struct_nodes(struct srcu_struct *ssp)
 {
 	int cpu;
 	int i;
@@ -148,14 +148,6 @@ static void init_srcu_struct_nodes(struct srcu_struct *ssp, bool is_static)
 		timer_setup(&sdp->delay_work, srcu_delay_timer, 0);
 		sdp->ssp = ssp;
 		sdp->grpmask = 1 << (cpu - sdp->mynode->grplo);
-		if (is_static)
-			continue;
-
-		/* Dynamically allocated, better be no srcu_read_locks()! */
-		for (i = 0; i < ARRAY_SIZE(sdp->srcu_lock_count); i++) {
-			sdp->srcu_lock_count[i] = 0;
-			sdp->srcu_unlock_count[i] = 0;
-		}
 	}
 }
 
@@ -179,7 +171,7 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
 		ssp->sda = alloc_percpu(struct srcu_data);
 	if (!ssp->sda)
 		return -ENOMEM;
-	init_srcu_struct_nodes(ssp, is_static);
+	init_srcu_struct_nodes(ssp);
 	ssp->srcu_gp_seq_needed_exp = 0;
 	ssp->srcu_last_gp_end = ktime_get_mono_fast_ns();
 	smp_store_release(&ssp->srcu_gp_seq_needed, 0); /* Init done. */
-- 
2.25.1