From 989a2979205dd34269382b357e6d4b4b6956b889 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 14 Apr 2010 09:55:35 +0000 Subject: [PATCH] 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: Eric Dumazet Cc: Paul E. McKenney Cc: Lai Jiangshan Signed-off-by: David S. Miller --- fs/fcntl.c | 66 ++++++++++++++++++++++++++--------------- include/linux/fs.h | 12 ++++---- net/socket.c | 73 +++++++--------------------------------------- 3 files changed, 59 insertions(+), 92 deletions(-) diff --git a/fs/fcntl.c b/fs/fcntl.c index 452d02f9075e..0a140741b39e 100644 --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -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; } @@ -704,37 +718,41 @@ 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; + struct fown_struct *fown; if (fa->magic != FASYNC_MAGIC) { printk(KERN_ERR "kill_fasync: bad magic number in " "fasync_struct!\n"); return; } - 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_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); + } + 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) { /* First a quick test without locking: usually * 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); diff --git a/include/linux/fs.h b/include/linux/fs.h index 39d57bc6cc71..018d382f6f92 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1280,10 +1280,12 @@ static inline int lock_may_write(struct inode *inode, loff_t start, struct fasync_struct { - int magic; - int fa_fd; - struct fasync_struct *fa_next; /* singly linked list */ - struct file *fa_file; + 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); diff --git a/net/socket.c b/net/socket.c index 35bc198bbf68..9822081eab38 100644 --- a/net/socket.c +++ b/net/socket.c @@ -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; + struct socket *sock = filp->private_data; + struct sock *sk = sock->sk; - if (on) { - fna = kmalloc(sizeof(struct fasync_struct), GFP_KERNEL); - if (fna == NULL) - return -ENOMEM; - } - - sock = filp->private_data; - - 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; + fasync_helper(fd, filp, on, &sock->fasync_list); + + if (!sock->fasync_list) + sock_reset_flag(sk, SOCK_FASYNC); else - filp->f_flags &= ~FASYNC; - spin_unlock(&filp->f_lock); - - prev = &(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); - } - } -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; }