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netpoll: Use rtnl_dereference() for npinfo pointer access

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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 <herbert@gondor.apana.org.au>
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Link: https://patch.msgid.link/20241202-netpoll_rcu_herbet_fix-v2-1-2b9d58edc76a@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Breno Leitao 2024-12-02 16:22:05 -08:00 committed by Jakub Kicinski
parent bb18265c3a
commit a9ab02ed97
1 changed files with 2 additions and 2 deletions
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4
net/core/netpoll.c
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@ -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);
}