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ipv6: Remove rcu_read_lock() in fib6_get_table().

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Once allocated, the IPv6 routing table is not freed until
netns is dismantled.

fib6_get_table() uses rcu_read_lock() while iterating
net->ipv6.fib_table_hash[], but it's not needed and
rather confusing.

Because some callers have this pattern,

  table = fib6_get_table();

  rcu_read_lock();
  /* ... use table here ... */
  rcu_read_unlock();

  [ See: addrconf_get_prefix_route(), ip6_route_del(),
         rt6_get_route_info(), rt6_get_dflt_router() ]

and this looks illegal but is actually safe.

Let's remove rcu_read_lock() in fib6_get_table() and pass true
to the last argument of hlist_for_each_entry_rcu() to bypass
the RCU check.

Note that protection is not needed but RCU helper is used to
avoid data-race.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250516022759.44392-2-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Kuniyuki Iwashima
2025-05-15 19:27:17 -07:00
committed by Jakub Kicinski
parent 5b1ced4469
commit f1a8d107d9
1 changed files with 10 additions and 12 deletions
Download Patch File Download Diff File Expand all files Collapse all files

22
net/ipv6/ip6_fib.c
View File

@@ -281,22 +281,20 @@ EXPORT_SYMBOL_GPL(fib6_new_table);
struct fib6_table *fib6_get_table(struct net *net, u32 id)
{
struct fib6_table *tb;
struct hlist_head *head;
unsigned int h;
struct fib6_table *tb;
if (id == 0)
if (!id)
id = RT6_TABLE_MAIN;
h = id & (FIB6_TABLE_HASHSZ - 1);
rcu_read_lock();
head = &net->ipv6.fib_table_hash[h];
hlist_for_each_entry_rcu(tb, head, tb6_hlist) {
if (tb->tb6_id == id) {
rcu_read_unlock();
head = &net->ipv6.fib_table_hash[id & (FIB6_TABLE_HASHSZ - 1)];
/* See comment in fib6_link_table(). RCU is not required,
* but rcu_dereference_raw() is used to avoid data-race.
*/
hlist_for_each_entry_rcu(tb, head, tb6_hlist, true)
if (tb->tb6_id == id)
return tb;
}
}
rcu_read_unlock();
return NULL;
}