[PATCH 6.6.y 1/4] netpoll: remove netpoll_srcu

[Sasha Levin <sashal@kernel.org>]

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 9a95eedc81deb86af1ac56f2c2bfe8306b27b82a ]

netpoll_srcu is currently used from netpoll_poll_disable() and
__netpoll_cleanup()

Both functions run under RTNL, using netpoll_srcu adds confusion
and no additional protection.

Moreover the synchronize_srcu() call in __netpoll_cleanup() is
performed before clearing np->dev->npinfo, which violates RCU rules.

After this patch, netpoll_poll_disable() and netpoll_poll_enable()
simply use rtnl_dereference().

This saves a big chunk of memory (more than 192KB on platforms
with 512 cpus)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20240905084909.2082486-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 49c8d2c1f94c ("net: netpoll: fix incorrect refcount handling causing incorrect cleanup")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/core/netpoll.c | 15 ++++-----------
 1 file changed, 4 insertions(+), 11 deletions(-)

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 2bdb1e84c6c8a..8c3379c1ecf07 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -48,8 +48,6 @@
 
 static struct sk_buff_head skb_pool;
 
-DEFINE_STATIC_SRCU(netpoll_srcu);
-
 #define USEC_PER_POLL	50
 
 #define MAX_SKB_SIZE							\
@@ -220,24 +218,21 @@ EXPORT_SYMBOL(netpoll_poll_dev);
 void netpoll_poll_disable(struct net_device *dev)
 {
 	struct netpoll_info *ni;
-	int idx;
+
 	might_sleep();
-	idx = srcu_read_lock(&netpoll_srcu);
-	ni = srcu_dereference(dev->npinfo, &netpoll_srcu);
+	ni = rtnl_dereference(dev->npinfo);
 	if (ni)
 		down(&ni->dev_lock);
-	srcu_read_unlock(&netpoll_srcu, idx);
 }
 EXPORT_SYMBOL(netpoll_poll_disable);
 
 void netpoll_poll_enable(struct net_device *dev)
 {
 	struct netpoll_info *ni;
-	rcu_read_lock();
-	ni = rcu_dereference(dev->npinfo);
+
+	ni = rtnl_dereference(dev->npinfo);
 	if (ni)
 		up(&ni->dev_lock);
-	rcu_read_unlock();
 }
 EXPORT_SYMBOL(netpoll_poll_enable);
 
@@ -843,8 +838,6 @@ void __netpoll_cleanup(struct netpoll *np)
 	if (!npinfo)
 		return;
 
-	synchronize_srcu(&netpoll_srcu);
-
 	if (refcount_dec_and_test(&npinfo->refcnt)) {
 		const struct net_device_ops *ops;
 
-- 
2.51.0