netdev - [PATCH net-next v2 3/4] devlink: expose get/put functions

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Date:   Sat, 30 Oct 2021 10:18:50 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     davem@...emloft.net
Cc:     netdev@...r.kernel.org, jiri@...nulli.us, leon@...nel.org,
        mkubecek@...e.cz, andrew@...n.ch, f.fainelli@...il.com,
        Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH net-next v2 3/4] devlink: expose get/put functions

Allow those who hold implicit reference on a devlink instance
to try to take a full ref on it. This will be used from netdev
code which has an implicit ref because of driver call ordering.

Note that after recent changes devlink_unregister() may happen
before netdev unregister, but devlink_free() should still happen
after, so we are safe to try, but we can't just refcount_inc()
and assume it's not zero.

Signed-off-by: Jakub Kicinski <kuba@...nel.org>
---
 include/net/devlink.h | 12 ++++++++++++
 net/core/devlink.c    |  8 +++++---
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/include/net/devlink.h b/include/net/devlink.h
index 1b1317d378de..991ce48f77ca 100644
--- a/include/net/devlink.h
+++ b/include/net/devlink.h
@@ -1726,6 +1726,9 @@ devlink_trap_policers_unregister(struct devlink *devlink,
 
 #if IS_ENABLED(CONFIG_NET_DEVLINK)
 
+struct devlink *__must_check devlink_try_get(struct devlink *devlink);
+void devlink_put(struct devlink *devlink);
+
 void devlink_compat_running_version(struct net_device *dev,
 				    char *buf, size_t len);
 int devlink_compat_flash_update(struct net_device *dev, const char *file_name);
@@ -1736,6 +1739,15 @@ int devlink_compat_switch_id_get(struct net_device *dev,
 
 #else
 
+static inline struct devlink *devlink_try_get(struct devlink *devlink)
+{
+	return NULL;
+}
+
+static inline void devlink_put(struct devlink *devlink)
+{
+}
+
 static inline void
 devlink_compat_running_version(struct net_device *dev, char *buf, size_t len)
 {
diff --git a/net/core/devlink.c b/net/core/devlink.c
index 2d8abe88c673..100d87fd3f65 100644
--- a/net/core/devlink.c
+++ b/net/core/devlink.c
@@ -182,15 +182,17 @@ struct net *devlink_net(const struct devlink *devlink)
 }
 EXPORT_SYMBOL_GPL(devlink_net);
 
-static void devlink_put(struct devlink *devlink)
+void devlink_put(struct devlink *devlink)
 {
 	if (refcount_dec_and_test(&devlink->refcount))
 		complete(&devlink->comp);
 }
 
-static bool __must_check devlink_try_get(struct devlink *devlink)
+struct devlink *__must_check devlink_try_get(struct devlink *devlink)
 {
-	return refcount_inc_not_zero(&devlink->refcount);
+	if (refcount_inc_not_zero(&devlink->refcount))
+		return devlink;
+	return NULL;
 }
 
 static struct devlink *devlink_get_from_attrs(struct net *net,
-- 
2.31.1