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mptcp: pm: lockless list traversal to dump endp

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To return an endpoint to the userspace via Netlink, and to dump all of
them, the endpoint list was iterated while holding the pernet->lock, but
only to read the content of the list.

In these cases, the spin locks can be replaced by RCU read ones, and use
the _rcu variants to iterate over the entries list in a lockless way.

Note that the __lookup_addr_by_id() helper has been modified to use the
_rcu variants of list_for_each_entry(), but with an extra conditions, so
it can be called either while the RCU read lock is held, or when the
associated pernet->lock is held.

Reviewed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20241115-net-next-mptcp-pm-lockless-dump-v1-1-f4a1bcb4ca2c@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Matthieu Baerts (NGI0) 2024-11-15 17:52:34 +01:00 committed by Jakub Kicinski
parent cc84d89ad8
commit 3fbb27b7f8
1 changed files with 7 additions and 6 deletions
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13
net/mptcp/pm_netlink.c
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@ -512,7 +512,8 @@ __lookup_addr_by_id(struct pm_nl_pernet *pernet, unsigned int id)
{
struct mptcp_pm_addr_entry *entry;
list_for_each_entry(entry, &pernet->local_addr_list, list) {
list_for_each_entry_rcu(entry, &pernet->local_addr_list, list,
lockdep_is_held(&pernet->lock)) {
if (entry->addr.id == id)
return entry;
}
@ -1824,7 +1825,7 @@ int mptcp_pm_nl_get_addr(struct sk_buff *skb, struct genl_info *info)
goto fail;
}
spin_lock_bh(&pernet->lock);
rcu_read_lock();
entry = __lookup_addr_by_id(pernet, addr.addr.id);
if (!entry) {
GENL_SET_ERR_MSG(info, "address not found");
@ -1838,11 +1839,11 @@ int mptcp_pm_nl_get_addr(struct sk_buff *skb, struct genl_info *info)
genlmsg_end(msg, reply);
ret = genlmsg_reply(msg, info);
spin_unlock_bh(&pernet->lock);
rcu_read_unlock();
return ret;
unlock_fail:
spin_unlock_bh(&pernet->lock);
rcu_read_unlock();
fail:
nlmsg_free(msg);
@ -1866,7 +1867,7 @@ int mptcp_pm_nl_dump_addr(struct sk_buff *msg,
pernet = pm_nl_get_pernet(net);
spin_lock_bh(&pernet->lock);
rcu_read_lock();
for (i = id; i < MPTCP_PM_MAX_ADDR_ID + 1; i++) {
if (test_bit(i, pernet->id_bitmap)) {
entry = __lookup_addr_by_id(pernet, i);
@ -1891,7 +1892,7 @@ int mptcp_pm_nl_dump_addr(struct sk_buff *msg,
genlmsg_end(msg, hdr);
}
}
spin_unlock_bh(&pernet->lock);
rcu_read_unlock();
cb->args[0] = id;
return msg->len;