Commit 989a2979 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

fasync: RCU and fine grained locking 



kill_fasync() uses a central rwlock, candidate for RCU conversion, to
avoid cache line ping pongs on SMP.

fasync_remove_entry() and fasync_add_entry() can disable IRQS on a short
section instead during whole list scan.

Use a spinlock per fasync_struct to synchronize kill_fasync_rcu() and
fasync_{remove|add}_entry(). This spinlock is IRQ safe, so sock_fasync()
doesnt need its own implementation and can use fasync_helper(), to
reduce code size and complexity.

We can remove __kill_fasync() direct use in net/socket.c, and rename it
to kill_fasync_rcu().

Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent e5700aff

fs/fcntl.c

+42 −24
Original line number Diff line number Diff line
@@ -614,9 +614,15 @@ int send_sigurg(struct fown_struct *fown) 
	return ret;

}



static DEFINE_RWLOCK(fasync_lock);

static DEFINE_SPINLOCK(fasync_lock);

static struct kmem_cache *fasync_cache __read_mostly;



static void fasync_free_rcu(struct rcu_head *head)

{

	kmem_cache_free(fasync_cache,

			container_of(head, struct fasync_struct, fa_rcu));

}



/*

 * Remove a fasync entry. If successfully removed, return

 * positive and clear the FASYNC flag. If no entry exists,
@@ -625,8 +631,6 @@ static struct kmem_cache *fasync_cache __read_mostly; 
 * NOTE! It is very important that the FASYNC flag always

 * match the state "is the filp on a fasync list".

 *

 * We always take the 'filp->f_lock', in since fasync_lock

 * needs to be irq-safe.

 */

static int fasync_remove_entry(struct file *filp, struct fasync_struct **fapp)

{
@@ -634,17 +638,22 @@ static int fasync_remove_entry(struct file *filp, struct fasync_struct **fapp) 
	int result = 0;



	spin_lock(&filp->f_lock);

	write_lock_irq(&fasync_lock);

	spin_lock(&fasync_lock);

	for (fp = fapp; (fa = *fp) != NULL; fp = &fa->fa_next) {

		if (fa->fa_file != filp)

			continue;



		spin_lock_irq(&fa->fa_lock);

		fa->fa_file = NULL;

		spin_unlock_irq(&fa->fa_lock);



		*fp = fa->fa_next;

		kmem_cache_free(fasync_cache, fa);

		call_rcu(&fa->fa_rcu, fasync_free_rcu);

		filp->f_flags &= ~FASYNC;

		result = 1;

		break;

	}

	write_unlock_irq(&fasync_lock);

	spin_unlock(&fasync_lock);

	spin_unlock(&filp->f_lock);

	return result;

}
@@ -666,25 +675,30 @@ static int fasync_add_entry(int fd, struct file *filp, struct fasync_struct **fa 
		return -ENOMEM;



	spin_lock(&filp->f_lock);

	write_lock_irq(&fasync_lock);

	spin_lock(&fasync_lock);

	for (fp = fapp; (fa = *fp) != NULL; fp = &fa->fa_next) {

		if (fa->fa_file != filp)

			continue;



		spin_lock_irq(&fa->fa_lock);

		fa->fa_fd = fd;

		spin_unlock_irq(&fa->fa_lock);



		kmem_cache_free(fasync_cache, new);

		goto out;

	}



	spin_lock_init(&new->fa_lock);

	new->magic = FASYNC_MAGIC;

	new->fa_file = filp;

	new->fa_fd = fd;

	new->fa_next = *fapp;

	*fapp = new;

	rcu_assign_pointer(*fapp, new);

	result = 1;

	filp->f_flags |= FASYNC;



out:

	write_unlock_irq(&fasync_lock);

	spin_unlock(&fasync_lock);

	spin_unlock(&filp->f_lock);

	return result;

}
@@ -704,7 +718,10 @@ int fasync_helper(int fd, struct file * filp, int on, struct fasync_struct **fap 


EXPORT_SYMBOL(fasync_helper);



void __kill_fasync(struct fasync_struct *fa, int sig, int band)

/*

 * rcu_read_lock() is held

 */

static void kill_fasync_rcu(struct fasync_struct *fa, int sig, int band)

{

	while (fa) {

		struct fown_struct *fown;
@@ -713,17 +730,19 @@ void __kill_fasync(struct fasync_struct *fa, int sig, int band) 
			       "fasync_struct!\n");

			return;

		}

		spin_lock(&fa->fa_lock);

		if (fa->fa_file) {

			fown = &fa->fa_file->f_owner;

			/* Don't send SIGURG to processes which have not set a

			   queued signum: SIGURG has its own default signalling

			   mechanism. */

			if (!(sig == SIGURG && fown->signum == 0))

				send_sigio(fown, fa->fa_fd, band);

		fa = fa->fa_next;

		}

		spin_unlock(&fa->fa_lock);

		fa = rcu_dereference(fa->fa_next);

	}

}



EXPORT_SYMBOL(__kill_fasync);



void kill_fasync(struct fasync_struct **fp, int sig, int band)

{
@@ -731,10 +750,9 @@ void kill_fasync(struct fasync_struct **fp, int sig, int band) 
	 * the list is empty.

	 */

	if (*fp) {

		read_lock(&fasync_lock);

		/* reread *fp after obtaining the lock */

		__kill_fasync(*fp, sig, band);

		read_unlock(&fasync_lock);

		rcu_read_lock();

		kill_fasync_rcu(rcu_dereference(*fp), sig, band);

		rcu_read_unlock();

	}

}

EXPORT_SYMBOL(kill_fasync);

include/linux/fs.h

+6 −6
Original line number Diff line number Diff line
@@ -1280,10 +1280,12 @@ static inline int lock_may_write(struct inode *inode, loff_t start, 




struct fasync_struct {

	spinlock_t		fa_lock;

	int			magic;

	int			fa_fd;

	struct fasync_struct	*fa_next; /* singly linked list */

	struct file		*fa_file;

	struct rcu_head		fa_rcu;

};



#define FASYNC_MAGIC 0x4601
@@ -1292,8 +1294,6 @@ struct fasync_struct { 
extern int fasync_helper(int, struct file *, int, struct fasync_struct **);

/* can be called from interrupts */

extern void kill_fasync(struct fasync_struct **, int, int);

/* only for net: no internal synchronization */

extern void __kill_fasync(struct fasync_struct *, int, int);



extern int __f_setown(struct file *filp, struct pid *, enum pid_type, int force);

extern int f_setown(struct file *filp, unsigned long arg, int force);

net/socket.c

+11 −62
Original line number Diff line number Diff line
@@ -1067,78 +1067,27 @@ static int sock_close(struct inode *inode, struct file *filp) 
 *	1. fasync_list is modified only under process context socket lock

 *	   i.e. under semaphore.

 *	2. fasync_list is used under read_lock(&sk->sk_callback_lock)

 *	   or under socket lock.

 *	3. fasync_list can be used from softirq context, so that

 *	   modification under socket lock have to be enhanced with

 *	   write_lock_bh(&sk->sk_callback_lock).

 *							--ANK (990710)

 *	   or under socket lock

 */



static int sock_fasync(int fd, struct file *filp, int on)

{

	struct fasync_struct *fa, *fna = NULL, **prev;

	struct socket *sock;

	struct sock *sk;



	if (on) {

		fna = kmalloc(sizeof(struct fasync_struct), GFP_KERNEL);

		if (fna == NULL)

			return -ENOMEM;

	}



	sock = filp->private_data;

	struct socket *sock = filp->private_data;

	struct sock *sk = sock->sk;



	sk = sock->sk;

	if (sk == NULL) {

		kfree(fna);

	if (sk == NULL)

		return -EINVAL;

	}



	lock_sock(sk);



	spin_lock(&filp->f_lock);

	if (on)

		filp->f_flags |= FASYNC;

	else

		filp->f_flags &= ~FASYNC;

	spin_unlock(&filp->f_lock);



	prev = &(sock->fasync_list);

	fasync_helper(fd, filp, on, &sock->fasync_list);



	for (fa = *prev; fa != NULL; prev = &fa->fa_next, fa = *prev)

		if (fa->fa_file == filp)

			break;



	if (on) {

		if (fa != NULL) {

			write_lock_bh(&sk->sk_callback_lock);

			fa->fa_fd = fd;

			write_unlock_bh(&sk->sk_callback_lock);



			kfree(fna);

			goto out;

		}

		fna->fa_file = filp;

		fna->fa_fd = fd;

		fna->magic = FASYNC_MAGIC;

		fna->fa_next = sock->fasync_list;

		write_lock_bh(&sk->sk_callback_lock);

		sock->fasync_list = fna;

		sock_set_flag(sk, SOCK_FASYNC);

		write_unlock_bh(&sk->sk_callback_lock);

	} else {

		if (fa != NULL) {

			write_lock_bh(&sk->sk_callback_lock);

			*prev = fa->fa_next;

	if (!sock->fasync_list)

		sock_reset_flag(sk, SOCK_FASYNC);

			write_unlock_bh(&sk->sk_callback_lock);

			kfree(fa);

		}

	}

	else

		sock_set_flag(sk, SOCK_FASYNC);



out:

	release_sock(sock->sk);

	release_sock(sk);

	return 0;

}
@@ -1159,10 +1108,10 @@ int sock_wake_async(struct socket *sock, int how, int band) 
		/* fall through */

	case SOCK_WAKE_IO:

call_kill:

		__kill_fasync(sock->fasync_list, SIGIO, band);

		kill_fasync(&sock->fasync_list, SIGIO, band);

		break;

	case SOCK_WAKE_URG:

		__kill_fasync(sock->fasync_list, SIGURG, band);

		kill_fasync(&sock->fasync_list, SIGURG, band);

	}

	return 0;

}

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