linux-kernel - [PATCH 3/3] locking/static_key: don't take sleeping locks in __static_key_slow_dec

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Message-Id: <20190330000854.30142-4-jakub.kicinski@netronome.com>
Date:   Fri, 29 Mar 2019 17:08:54 -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 3/3] locking/static_key: don't take sleeping locks in __static_key_slow_dec_deferred()

Changing jump_label state is protected by jump_label_lock().
Rate limited static_key_slow_dec(), however, will never
directly call jump_label_update(), it will schedule a delayed
work instead.  Therefore it's unnecessary to take both the
cpus_read_lock() and jump_label_lock().

This allows static_key_slow_dec_deferred() to be called
from atomic contexts, like socket destructing in net/tls,
without the need for another indirection.

Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
Reviewed-by: Simon Horman <simon.horman@...ronome.com>
---
 kernel/jump_label.c | 32 +++++++++++++-------------------
 1 file changed, 13 insertions(+), 19 deletions(-)

diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 02c3d11264dd..de6efdecc70d 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -221,9 +221,7 @@ static bool static_key_slow_try_dec(struct static_key *key)
 	return true;
 }
 
-static void __static_key_slow_dec_cpuslocked(struct static_key *key,
-					   unsigned long rate_limit,
-					   struct delayed_work *work)
+static void __static_key_slow_dec_cpuslocked(struct static_key *key)
 {
 	lockdep_assert_cpus_held();
 
@@ -231,23 +229,15 @@ static void __static_key_slow_dec_cpuslocked(struct static_key *key,
 		return;
 
 	jump_label_lock();
-	if (atomic_dec_and_test(&key->enabled)) {
-		if (rate_limit) {
-			atomic_inc(&key->enabled);
-			schedule_delayed_work(work, rate_limit);
-		} else {
-			jump_label_update(key);
-		}
-	}
+	if (atomic_dec_and_test(&key->enabled))
+		jump_label_update(key);
 	jump_label_unlock();
 }
 
-static void __static_key_slow_dec(struct static_key *key,
-				  unsigned long rate_limit,
-				  struct delayed_work *work)
+static void __static_key_slow_dec(struct static_key *key)
 {
 	cpus_read_lock();
-	__static_key_slow_dec_cpuslocked(key, rate_limit, work);
+	__static_key_slow_dec_cpuslocked(key);
 	cpus_read_unlock();
 }
 
@@ -255,21 +245,21 @@ void jump_label_update_timeout(struct work_struct *work)
 {
 	struct static_key_deferred *key =
 		container_of(work, struct static_key_deferred, work.work);
-	__static_key_slow_dec(&key->key, 0, NULL);
+	__static_key_slow_dec(&key->key);
 }
 EXPORT_SYMBOL_GPL(jump_label_update_timeout);
 
 void static_key_slow_dec(struct static_key *key)
 {
 	STATIC_KEY_CHECK_USE(key);
-	__static_key_slow_dec(key, 0, NULL);
+	__static_key_slow_dec(key);
 }
 EXPORT_SYMBOL_GPL(static_key_slow_dec);
 
 void static_key_slow_dec_cpuslocked(struct static_key *key)
 {
 	STATIC_KEY_CHECK_USE(key);
-	__static_key_slow_dec_cpuslocked(key, 0, NULL);
+	__static_key_slow_dec_cpuslocked(key);
 }
 
 void __static_key_slow_dec_deferred(struct static_key *key,
@@ -277,7 +267,11 @@ void __static_key_slow_dec_deferred(struct static_key *key,
 				    unsigned long timeout)
 {
 	STATIC_KEY_CHECK_USE(key);
-	__static_key_slow_dec(key, timeout, work);
+
+	if (static_key_slow_try_dec(key))
+		return;
+
+	schedule_delayed_work(work, timeout);
 }
 EXPORT_SYMBOL_GPL(__static_key_slow_dec_deferred);
 
-- 
2.21.0