netdev - [Patch net] smc: use RCU version of lower netdev searching

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Message-Id: <20240912000446.1025844-1-xiyou.wangcong@gmail.com>
Date: Wed, 11 Sep 2024 17:04:46 -0700
From: Cong Wang <xiyou.wangcong@...il.com>
To: netdev@...r.kernel.org
Cc: Cong Wang <cong.wang@...edance.com>,
	syzbot+c75d1de73d3b8b76272f@...kaller.appspotmail.com,
	Wenjia Zhang <wenjia@...ux.ibm.com>,
	Jan Karcher <jaka@...ux.ibm.com>,
	"D. Wythe" <alibuda@...ux.alibaba.com>,
	Tony Lu <tonylu@...ux.alibaba.com>,
	Wen Gu <guwen@...ux.alibaba.com>
Subject: [Patch net] smc: use RCU version of lower netdev searching

From: Cong Wang <cong.wang@...edance.com>

Both netdev_walk_all_lower_dev() and netdev_lower_get_next() have a
RCU version, which are netdev_walk_all_lower_dev_rcu() and
netdev_next_lower_dev_rcu(). Switching to the RCU version would
eliminate the need for RTL lock, thus could amend the deadlock
complaints from syzbot. And it could also potentially speed up its
callers like smc_connect().

Reported-by: syzbot+c75d1de73d3b8b76272f@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c75d1de73d3b8b76272f
Cc: Wenjia Zhang <wenjia@...ux.ibm.com>
Cc: Jan Karcher <jaka@...ux.ibm.com>
Cc: "D. Wythe" <alibuda@...ux.alibaba.com>
Cc: Tony Lu <tonylu@...ux.alibaba.com>
Cc: Wen Gu <guwen@...ux.alibaba.com>
Signed-off-by: Cong Wang <cong.wang@...edance.com>
---
 net/smc/smc_core.c |  6 +++---
 net/smc/smc_pnet.c | 14 +++++++-------
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
index 3b95828d9976..574039b7d456 100644
--- a/net/smc/smc_core.c
+++ b/net/smc/smc_core.c
@@ -1850,9 +1850,9 @@ int smc_vlan_by_tcpsk(struct socket *clcsock, struct smc_init_info *ini)
 	}
 
 	priv.data = (void *)&ini->vlan_id;
-	rtnl_lock();
-	netdev_walk_all_lower_dev(ndev, smc_vlan_by_tcpsk_walk, &priv);
-	rtnl_unlock();
+	rcu_read_lock();
+	netdev_walk_all_lower_dev_rcu(ndev, smc_vlan_by_tcpsk_walk, &priv);
+	rcu_read_unlock();
 
 out_rel:
 	dst_release(dst);
diff --git a/net/smc/smc_pnet.c b/net/smc/smc_pnet.c
index 2adb92b8c469..b8ee6da08638 100644
--- a/net/smc/smc_pnet.c
+++ b/net/smc/smc_pnet.c
@@ -29,7 +29,6 @@
 #include "smc_ism.h"
 #include "smc_core.h"
 
-static struct net_device *__pnet_find_base_ndev(struct net_device *ndev);
 static struct net_device *pnet_find_base_ndev(struct net_device *ndev);
 
 static const struct nla_policy smc_pnet_policy[SMC_PNETID_MAX + 1] = {
@@ -791,7 +790,7 @@ static void smc_pnet_add_base_pnetid(struct net *net, struct net_device *dev,
 {
 	struct net_device *base_dev;
 
-	base_dev = __pnet_find_base_ndev(dev);
+	base_dev = pnet_find_base_ndev(dev);
 	if (base_dev->flags & IFF_UP &&
 	    !smc_pnetid_by_dev_port(base_dev->dev.parent, base_dev->dev_port,
 				    ndev_pnetid)) {
@@ -857,7 +856,7 @@ static int smc_pnet_netdev_event(struct notifier_block *this,
 		smc_pnet_add_base_pnetid(net, event_dev, ndev_pnetid);
 		return NOTIFY_OK;
 	case NETDEV_DOWN:
-		event_dev = __pnet_find_base_ndev(event_dev);
+		event_dev = pnet_find_base_ndev(event_dev);
 		if (!smc_pnetid_by_dev_port(event_dev->dev.parent,
 					    event_dev->dev_port, ndev_pnetid)) {
 			/* remove from PNETIDs list */
@@ -925,7 +924,6 @@ static struct net_device *__pnet_find_base_ndev(struct net_device *ndev)
 {
 	int i, nest_lvl;
 
-	ASSERT_RTNL();
 	nest_lvl = ndev->lower_level;
 	for (i = 0; i < nest_lvl; i++) {
 		struct list_head *lower = &ndev->adj_list.lower;
@@ -933,7 +931,9 @@ static struct net_device *__pnet_find_base_ndev(struct net_device *ndev)
 		if (list_empty(lower))
 			break;
 		lower = lower->next;
-		ndev = netdev_lower_get_next(ndev, &lower);
+		ndev = netdev_next_lower_dev_rcu(ndev, &lower);
+		if (!ndev)
+			break;
 	}
 	return ndev;
 }
@@ -945,9 +945,9 @@ static struct net_device *__pnet_find_base_ndev(struct net_device *ndev)
  */
 static struct net_device *pnet_find_base_ndev(struct net_device *ndev)
 {
-	rtnl_lock();
+	rcu_read_lock();
 	ndev = __pnet_find_base_ndev(ndev);
-	rtnl_unlock();
+	rcu_read_unlock();
 	return ndev;
 }
 
-- 
2.34.1