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ipv4: fib: Drop RTNL annotation for net->ipv4.fib_table_hash[].

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fib_newrule() will drop RTNL except for the first IPv4 rule.

net->ipv4.fib_table_hash[] will be read with no protection,
but this is fine because fib_table is not destroyed until
netns dismantle except for the merged main/local table.

fib_unmerge() will continue to be called under RTNL, so other
readers (fib_flush() and fib_info_notify_update()) just have
to care about the concurrent hlist_add().

IPv6 and IPMR/IP6MR also take this strategy and use RCU helpers
to avoid data race against concurrent hlist_add().

Let's not use lockdep_rtnl_is_held() and rcu_dereference_rtnl()
for net->ipv4.fib_table_hash[].

Note that commit a7e5353123 ("fib_trie: Make fib_table rcu
safe") started to use the _safe version in fib_flush(), but it
is not needed thanks to RTNL.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260629181226.1929658-5-kuniyu@google.com
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Kuniyuki Iwashima
2026-06-29 18:10:56 +00:00
committed by Paolo Abeni
parent 4b8f5c974d
commit 763a943710
3 changed files with 16 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
include/net/ip_fib.h
View File

@@ -302,7 +302,8 @@ static inline struct fib_table *fib_get_table(struct net *net, u32 id)
&net->ipv4.fib_table_hash[TABLE_LOCAL_INDEX] :
&net->ipv4.fib_table_hash[TABLE_MAIN_INDEX];
tb_hlist = rcu_dereference_rtnl(hlist_first_rcu(ptr));
/* Only fib4_rules_init() adds fib_table. */
tb_hlist = rcu_dereference_protected(hlist_first_rcu(ptr), true);
return hlist_entry(tb_hlist, struct fib_table, tb_hlist);
}

23
net/ipv4/fib_frontend.c
View File

@@ -126,24 +126,28 @@ struct fib_table *fib_new_table(struct net *net, u32 id)
}
EXPORT_SYMBOL_GPL(fib_new_table);
/* caller must hold either rtnl or rcu read lock */
struct fib_table *fib_get_table(struct net *net, u32 id)
{
struct fib_table *tb;
struct fib_table *tb = NULL;
struct hlist_head *head;
unsigned int h;
if (id == 0)
id = RT_TABLE_MAIN;
h = id & (FIB_TABLE_HASHSZ - 1);
head = &net->ipv4.fib_table_hash[h];
hlist_for_each_entry_rcu(tb, head, tb_hlist,
lockdep_rtnl_is_held()) {
/* fib_table is not destroyed until ip_fib_net_exit()
* except for the merged main/local table.
* fib_unmerge() is called under RTNL, so other readers
* under RTNL (e.g. fib_flush(), fib_info_notify_update())
* can safely traverse the list with rcu_dereference_raw().
*/
hlist_for_each_entry_rcu(tb, head, tb_hlist, true)
if (tb->tb_id == id)
return tb;
}
return NULL;
break;
return tb;
}
#endif /* CONFIG_IP_MULTIPLE_TABLES */
@@ -206,10 +210,9 @@ void fib_flush(struct net *net)
for (h = 0; h < FIB_TABLE_HASHSZ; h++) {
struct hlist_head *head = &net->ipv4.fib_table_hash[h];
struct hlist_node *tmp;
struct fib_table *tb;
hlist_for_each_entry_safe(tb, tmp, head, tb_hlist)
hlist_for_each_entry_rcu(tb, head, tb_hlist, true)
flushed += fib_table_flush(net, tb, false);
}

3
net/ipv4/fib_trie.c
View File

@@ -2137,8 +2137,7 @@ void fib_info_notify_update(struct net *net, struct nl_info *info)
struct hlist_head *head = &net->ipv4.fib_table_hash[h];
struct fib_table *tb;
hlist_for_each_entry_rcu(tb, head, tb_hlist,
lockdep_rtnl_is_held())
hlist_for_each_entry_rcu(tb, head, tb_hlist, true)
__fib_info_notify_update(net, tb, info);
}
}