From a9ab02ed97c654a9ea09afb3e6294cea3768c388 Mon Sep 17 00:00:00 2001 From: Breno Leitao Date: Mon, 2 Dec 2024 16:22:05 -0800 Subject: [PATCH] netpoll: Use rtnl_dereference() for npinfo pointer access In the __netpoll_setup() function, when accessing the device's npinfo pointer, replace rcu_access_pointer() with rtnl_dereference(). This change is more appropriate, as suggested by Herbert Xu[1]. The function is called with the RTNL mutex held, and the pointer is being dereferenced later, so, dereference earlier and just reuse the pointer for the if/else. The replacement ensures correct pointer access while maintaining the existing locking and RCU semantics of the netpoll subsystem. Link: https://lore.kernel.org/lkml/Zz1cKZYt1e7elibV@gondor.apana.org.au/ [1] Suggested-by: Herbert Xu Signed-off-by: Breno Leitao Reviewed-by: Jacob Keller Acked-by: Herbert Xu Link: https://patch.msgid.link/20241202-netpoll_rcu_herbet_fix-v2-1-2b9d58edc76a@debian.org Signed-off-by: Jakub Kicinski --- net/core/netpoll.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/core/netpoll.c b/net/core/netpoll.c index 2e459b9d88eb5..99e5aa9cc992f 100644 --- a/net/core/netpoll.c +++ b/net/core/netpoll.c @@ -634,7 +634,8 @@ int __netpoll_setup(struct netpoll *np, struct net_device *ndev) goto out; } - if (!rcu_access_pointer(ndev->npinfo)) { + npinfo = rtnl_dereference(ndev->npinfo); + if (!npinfo) { npinfo = kmalloc(sizeof(*npinfo), GFP_KERNEL); if (!npinfo) { err = -ENOMEM; @@ -654,7 +655,6 @@ int __netpoll_setup(struct netpoll *np, struct net_device *ndev) goto free_npinfo; } } else { - npinfo = rtnl_dereference(ndev->npinfo); refcount_inc(&npinfo->refcnt); }