Commit 19efbd93 authored by Kirill Tkhai's avatar Kirill Tkhai Committed by David S. Miller
Browse files

net: Kill net_mutex 



We take net_mutex, when there are !async pernet_operations
registered, and read locking of net_sem is not enough. But
we may get rid of taking the mutex, and just change the logic
to write lock net_sem in such cases. This obviously reduces
the number of lock operations, we do.

Signed-off-by: default avatarKirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent ffc385b9

include/linux/rtnetlink.h

+0 −1
Original line number Diff line number Diff line
@@ -35,7 +35,6 @@ extern int rtnl_trylock(void); 
extern int rtnl_is_locked(void);



extern wait_queue_head_t netdev_unregistering_wq;

extern struct mutex net_mutex;

extern struct rw_semaphore net_sem;



#ifdef CONFIG_PROVE_LOCKING

include/net/net_namespace.h

+7 −4
Original line number Diff line number Diff line
@@ -60,8 +60,11 @@ struct net { 


	struct list_head	list;		/* list of network namespaces */

	struct list_head	cleanup_list;	/* namespaces on death row */

	struct list_head	exit_list;	/* Use only net_mutex */



	struct list_head	exit_list;	/* To linked to call pernet exit

						 * methods on dead net (net_sem

						 * read locked), or to unregister

						 * pernet ops (net_sem wr locked).

						 */

	struct user_namespace   *user_ns;	/* Owning user namespace */

	struct ucounts		*ucounts;

	spinlock_t		nsid_lock;
@@ -89,7 +92,7 @@ struct net { 
	/* core fib_rules */

	struct list_head	rules_ops;



	struct list_head	fib_notifier_ops;  /* protected by net_mutex */

	struct list_head	fib_notifier_ops;  /* protected by net_sem */



	struct net_device       *loopback_dev;          /* The loopback */

	struct netns_core	core;
@@ -316,7 +319,7 @@ struct pernet_operations { 
	/*

	 * Indicates above methods are allowed to be executed in parallel

	 * with methods of any other pernet_operations, i.e. they are not

	 * need synchronization via net_mutex.

	 * need write locked net_sem.

	 */

	bool async;

};

net/core/net_namespace.c

+32 −21
Original line number Diff line number Diff line
@@ -29,8 +29,6 @@ 


static LIST_HEAD(pernet_list);

static struct list_head *first_device = &pernet_list;

/* Used only if there are !async pernet_operations registered */

DEFINE_MUTEX(net_mutex);



LIST_HEAD(net_namespace_list);

EXPORT_SYMBOL_GPL(net_namespace_list);
@@ -407,6 +405,7 @@ struct net *copy_net_ns(unsigned long flags, 
{

	struct ucounts *ucounts;

	struct net *net;

	unsigned write;

	int rv;



	if (!(flags & CLONE_NEWNET))
@@ -424,20 +423,26 @@ struct net *copy_net_ns(unsigned long flags, 
	refcount_set(&net->passive, 1);

	net->ucounts = ucounts;

	get_user_ns(user_ns);



again:

	write = READ_ONCE(nr_sync_pernet_ops);

	if (write)

		rv = down_write_killable(&net_sem);

	else

		rv = down_read_killable(&net_sem);

	if (rv < 0)

		goto put_userns;

	if (nr_sync_pernet_ops) {

		rv = mutex_lock_killable(&net_mutex);

		if (rv < 0)

			goto up_read;



	if (!write && unlikely(READ_ONCE(nr_sync_pernet_ops))) {

		up_read(&net_sem);

		goto again;

	}

	rv = setup_net(net, user_ns);

	if (nr_sync_pernet_ops)

		mutex_unlock(&net_mutex);

up_read:



	if (write)

		up_write(&net_sem);

	else

		up_read(&net_sem);



	if (rv < 0) {

put_userns:

		put_user_ns(user_ns);
@@ -485,15 +490,23 @@ static void cleanup_net(struct work_struct *work) 
	struct net *net, *tmp, *last;

	struct list_head net_kill_list;

	LIST_HEAD(net_exit_list);

	unsigned write;



	/* Atomically snapshot the list of namespaces to cleanup */

	spin_lock_irq(&cleanup_list_lock);

	list_replace_init(&cleanup_list, &net_kill_list);

	spin_unlock_irq(&cleanup_list_lock);



again:

	write = READ_ONCE(nr_sync_pernet_ops);

	if (write)

		down_write(&net_sem);

	else

		down_read(&net_sem);

	if (nr_sync_pernet_ops)

		mutex_lock(&net_mutex);



	if (!write && unlikely(READ_ONCE(nr_sync_pernet_ops))) {

		up_read(&net_sem);

		goto again;

	}



	/* Don't let anyone else find us. */

	rtnl_lock();
@@ -528,13 +541,13 @@ static void cleanup_net(struct work_struct *work) 
	list_for_each_entry_reverse(ops, &pernet_list, list)

		ops_exit_list(ops, &net_exit_list);



	if (nr_sync_pernet_ops)

		mutex_unlock(&net_mutex);



	/* Free the net generic variables */

	list_for_each_entry_reverse(ops, &pernet_list, list)

		ops_free_list(ops, &net_exit_list);



	if (write)

		up_write(&net_sem);

	else

		up_read(&net_sem);



	/* Ensure there are no outstanding rcu callbacks using this
@@ -563,8 +576,6 @@ static void cleanup_net(struct work_struct *work) 
void net_ns_barrier(void)

{

	down_write(&net_sem);

	mutex_lock(&net_mutex);

	mutex_unlock(&net_mutex);

	up_write(&net_sem);

}

EXPORT_SYMBOL(net_ns_barrier);

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