linux-kernel - [PATCH 2/3] locking/static_key: factor out the fast path of static_key_slow

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Message-Id: <20190330000854.30142-3-jakub.kicinski@netronome.com>
Date:   Fri, 29 Mar 2019 17:08:53 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     peterz@...radead.org, tglx@...utronix.de
Cc:     ard.biesheuvel@...aro.org, yamada.masahiro@...ionext.com,
        mingo@...nel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, oss-drivers@...ronome.com,
        alexei.starovoitov@...il.com,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Simon Horman <simon.horman@...ronome.com>
Subject: [PATCH 2/3] locking/static_key: factor out the fast path of static_key_slow_dec()

static_key_slow_dec() checks if the atomic enable count is larger
than 1, and if so there decrements it before taking the jump_label_lock.
Move this logic into a helper for reuse in rate limitted keys.

Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
Reviewed-by: Simon Horman <simon.horman@...ronome.com>
---
 kernel/jump_label.c | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 73bbbaddbd9c..02c3d11264dd 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -202,13 +202,13 @@ void static_key_disable(struct static_key *key)
 }
 EXPORT_SYMBOL_GPL(static_key_disable);
 
-static void __static_key_slow_dec_cpuslocked(struct static_key *key,
-					   unsigned long rate_limit,
-					   struct delayed_work *work)
+static bool static_key_slow_try_dec(struct static_key *key)
 {
 	int val;
 
-	lockdep_assert_cpus_held();
+	val = atomic_fetch_add_unless(&key->enabled, -1, 1);
+	if (val == 1)
+		return false;
 
 	/*
 	 * The negative count check is valid even when a negative
@@ -217,11 +217,18 @@ static void __static_key_slow_dec_cpuslocked(struct static_key *key,
 	 * returns is unbalanced, because all other static_key_slow_inc()
 	 * instances block while the update is in progress.
 	 */
-	val = atomic_fetch_add_unless(&key->enabled, -1, 1);
-	if (val != 1) {
-		WARN(val < 0, "jump label: negative count!\n");
+	WARN(val < 0, "jump label: negative count!\n");
+	return true;
+}
+
+static void __static_key_slow_dec_cpuslocked(struct static_key *key,
+					   unsigned long rate_limit,
+					   struct delayed_work *work)
+{
+	lockdep_assert_cpus_held();
+
+	if (static_key_slow_try_dec(key))
 		return;
-	}
 
 	jump_label_lock();
 	if (atomic_dec_and_test(&key->enabled)) {
-- 
2.21.0