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net: expedite synchronize_net() for cleanup_net()

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cleanup_net() is the single thread responsible
for netns dismantles, and a serious bottleneck.

Before we can get per-netns RTNL, make sure
all synchronize_net() called from this thread
are using rcu_synchronize_expedited().

v3: deal with CONFIG_NET_NS=n

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Jesse Brandeburg <jbrandeburg@cloudflare.com>
Link: https://patch.msgid.link/20250114205531.967841-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet 2025-01-14 20:55:27 +00:00 • committed by Jakub Kicinski
parent 0b6f6593aa
commit 0734d7c3d9
3 changed files with 17 additions and 1 deletions
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2
include/net/net_namespace.h
View file

@ -210,6 +210,8 @@ void net_ns_barrier(void);
struct ns_common *get_net_ns(struct ns_common *ns);
struct net *get_net_ns_by_fd(int fd);
extern struct task_struct *cleanup_net_task;
#else /* CONFIG_NET_NS */
#include <linux/sched.h>
#include <linux/nsproxy.h>

11
net/core/dev.c
View file

@ -10099,6 +10099,15 @@ static void dev_index_release(struct net *net, int ifindex)
WARN_ON(xa_erase(&net->dev_by_index, ifindex));
}
static bool from_cleanup_net(void)
{
#ifdef CONFIG_NET_NS
return current == cleanup_net_task;
#else
return false;
#endif
}
/* Delayed registration/unregisteration */
LIST_HEAD(net_todo_list);
DECLARE_WAIT_QUEUE_HEAD(netdev_unregistering_wq);
@ -11474,7 +11483,7 @@ EXPORT_SYMBOL_GPL(alloc_netdev_dummy);
void synchronize_net(void)
{
might_sleep();
if (rtnl_is_locked())
if (from_cleanup_net() || rtnl_is_locked())
synchronize_rcu_expedited();
else
synchronize_rcu();

5
net/core/net_namespace.c
View file

@ -588,6 +588,8 @@ static void unhash_nsid(struct net *net, struct net *last)
static LLIST_HEAD(cleanup_list);
struct task_struct *cleanup_net_task;
static void cleanup_net(struct work_struct *work)
{
const struct pernet_operations *ops;
@ -596,6 +598,8 @@ static void cleanup_net(struct work_struct *work)
LIST_HEAD(net_exit_list);
LIST_HEAD(dev_kill_list);
cleanup_net_task = current;
/* Atomically snapshot the list of namespaces to cleanup */
net_kill_list = llist_del_all(&cleanup_list);
@ -670,6 +674,7 @@ static void cleanup_net(struct work_struct *work)
put_user_ns(net->user_ns);
net_free(net);
}
cleanup_net_task = NULL;
}
/**