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fasync: RCU and fine grained locking

Browse source 
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 <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Lai Jiangshan <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
This commit is contained in:
Eric Dumazet 2010-04-14 09:55:35 +00:00 • committed by David S. Miller
commit 989a297920
3 changed files with 59 additions and 92 deletions
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66
fs/fcntl.c
View file

@ -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);