* AV 1 Mar 1999
* Damn. Added missing check for ->dead in listen queues scanning.
*
+ * Miklos Szeredi 25 Jun 2007
+ * Reimplement with a cycle collecting algorithm. This should
+ * solve several problems with the previous code, like being racy
+ * wrt receive and holding up unrelated socket operations.
*/
#include <linux/kernel.h>
/* Internal data structures and random procedures: */
-#define GC_HEAD ((struct sock *)(-1))
-#define GC_ORPHAN ((struct sock *)(-3))
-
-static struct sock *gc_current = GC_HEAD; /* stack of objects to mark */
+static LIST_HEAD(gc_inflight_list);
+static LIST_HEAD(gc_candidates);
+static DEFINE_SPINLOCK(unix_gc_lock);
atomic_t unix_tot_inflight = ATOMIC_INIT(0);
{
struct sock *s = unix_get_socket(fp);
if(s) {
- atomic_inc(&unix_sk(s)->inflight);
+ struct unix_sock *u = unix_sk(s);
+ spin_lock(&unix_gc_lock);
+ if (atomic_inc_return(&u->inflight) == 1) {
+ BUG_ON(!list_empty(&u->link));
+ list_add_tail(&u->link, &gc_inflight_list);
+ } else {
+ BUG_ON(list_empty(&u->link));
+ }
atomic_inc(&unix_tot_inflight);
+ spin_unlock(&unix_gc_lock);
}
}
{
struct sock *s = unix_get_socket(fp);
if(s) {
- atomic_dec(&unix_sk(s)->inflight);
+ struct unix_sock *u = unix_sk(s);
+ spin_lock(&unix_gc_lock);
+ BUG_ON(list_empty(&u->link));
+ if (atomic_dec_and_test(&u->inflight))
+ list_del_init(&u->link);
atomic_dec(&unix_tot_inflight);
+ spin_unlock(&unix_gc_lock);
}
}
+static inline struct sk_buff *sock_queue_head(struct sock *sk)
+{
+ return (struct sk_buff *) &sk->sk_receive_queue;
+}
-/*
- * Garbage Collector Support Functions
- */
+#define receive_queue_for_each_skb(sk, next, skb) \
+ for (skb = sock_queue_head(sk)->next, next = skb->next; \
+ skb != sock_queue_head(sk); skb = next, next = skb->next)
-static inline struct sock *pop_stack(void)
+static void scan_inflight(struct sock *x, void (*func)(struct sock *),
+ struct sk_buff_head *hitlist)
{
- struct sock *p = gc_current;
- gc_current = unix_sk(p)->gc_tree;
- return p;
+ struct sk_buff *skb;
+ struct sk_buff *next;
+
+ spin_lock(&x->sk_receive_queue.lock);
+ receive_queue_for_each_skb(x, next, skb) {
+ /*
+ * Do we have file descriptors ?
+ */
+ if (UNIXCB(skb).fp) {
+ bool hit = false;
+ /*
+ * Process the descriptors of this socket
+ */
+ int nfd = UNIXCB(skb).fp->count;
+ struct file **fp = UNIXCB(skb).fp->fp;
+ while (nfd--) {
+ /*
+ * Get the socket the fd matches
+ * if it indeed does so
+ */
+ struct sock *sk = unix_get_socket(*fp++);
+ if(sk) {
+ hit = true;
+ func(sk);
+ }
+ }
+ if (hit && hitlist != NULL) {
+ __skb_unlink(skb, &x->sk_receive_queue);
+ __skb_queue_tail(hitlist, skb);
+ }
+ }
+ }
+ spin_unlock(&x->sk_receive_queue.lock);
}
-static inline int empty_stack(void)
+static void scan_children(struct sock *x, void (*func)(struct sock *),
+ struct sk_buff_head *hitlist)
{
- return gc_current == GC_HEAD;
+ if (x->sk_state != TCP_LISTEN)
+ scan_inflight(x, func, hitlist);
+ else {
+ struct sk_buff *skb;
+ struct sk_buff *next;
+ struct unix_sock *u;
+ LIST_HEAD(embryos);
+
+ /*
+ * For a listening socket collect the queued embryos
+ * and perform a scan on them as well.
+ */
+ spin_lock(&x->sk_receive_queue.lock);
+ receive_queue_for_each_skb(x, next, skb) {
+ u = unix_sk(skb->sk);
+
+ /*
+ * An embryo cannot be in-flight, so it's safe
+ * to use the list link.
+ */
+ BUG_ON(!list_empty(&u->link));
+ list_add_tail(&u->link, &embryos);
+ }
+ spin_unlock(&x->sk_receive_queue.lock);
+
+ while (!list_empty(&embryos)) {
+ u = list_entry(embryos.next, struct unix_sock, link);
+ scan_inflight(&u->sk, func, hitlist);
+ list_del_init(&u->link);
+ }
+ }
}
-static void maybe_unmark_and_push(struct sock *x)
+static void dec_inflight(struct sock *sk)
{
- struct unix_sock *u = unix_sk(x);
+ atomic_dec(&unix_sk(sk)->inflight);
+}
- if (u->gc_tree != GC_ORPHAN)
- return;
- sock_hold(x);
- u->gc_tree = gc_current;
- gc_current = x;
+static void inc_inflight(struct sock *sk)
+{
+ atomic_inc(&unix_sk(sk)->inflight);
}
+static void inc_inflight_move_tail(struct sock *sk)
+{
+ struct unix_sock *u = unix_sk(sk);
+
+ atomic_inc(&u->inflight);
+ /*
+ * If this is still a candidate, move it to the end of the
+ * list, so that it's checked even if it was already passed
+ * over
+ */
+ if (u->gc_candidate)
+ list_move_tail(&u->link, &gc_candidates);
+}
/* The external entry point: unix_gc() */
void unix_gc(void)
{
- static DEFINE_MUTEX(unix_gc_sem);
- int i;
- struct sock *s;
- struct sk_buff_head hitlist;
- struct sk_buff *skb;
+ static bool gc_in_progress = false;
- /*
- * Avoid a recursive GC.
- */
+ struct unix_sock *u;
+ struct unix_sock *next;
+ struct sk_buff_head hitlist;
+ struct list_head cursor;
- if (!mutex_trylock(&unix_gc_sem))
- return;
+ spin_lock(&unix_gc_lock);
- spin_lock(&unix_table_lock);
+ /* Avoid a recursive GC. */
+ if (gc_in_progress)
+ goto out;
- forall_unix_sockets(i, s)
- {
- unix_sk(s)->gc_tree = GC_ORPHAN;
- }
+ gc_in_progress = true;
/*
- * Everything is now marked
- */
-
- /* Invariant to be maintained:
- - everything unmarked is either:
- -- (a) on the stack, or
- -- (b) has all of its children unmarked
- - everything on the stack is always unmarked
- - nothing is ever pushed onto the stack twice, because:
- -- nothing previously unmarked is ever pushed on the stack
+ * First, select candidates for garbage collection. Only
+ * in-flight sockets are considered, and from those only ones
+ * which don't have any external reference.
+ *
+ * Holding unix_gc_lock will protect these candidates from
+ * being detached, and hence from gaining an external
+ * reference. This also means, that since there are no
+ * possible receivers, the receive queues of these sockets are
+ * static during the GC, even though the dequeue is done
+ * before the detach without atomicity guarantees.
*/
+ list_for_each_entry_safe(u, next, &gc_inflight_list, link) {
+ int total_refs;
+ int inflight_refs;
+
+ total_refs = file_count(u->sk.sk_socket->file);
+ inflight_refs = atomic_read(&u->inflight);
+
+ BUG_ON(inflight_refs < 1);
+ BUG_ON(total_refs < inflight_refs);
+ if (total_refs == inflight_refs) {
+ list_move_tail(&u->link, &gc_candidates);
+ u->gc_candidate = 1;
+ }
+ }
/*
- * Push root set
+ * Now remove all internal in-flight reference to children of
+ * the candidates.
*/
-
- forall_unix_sockets(i, s)
- {
- int open_count = 0;
-
- /*
- * If all instances of the descriptor are not
- * in flight we are in use.
- *
- * Special case: when socket s is embrion, it may be
- * hashed but still not in queue of listening socket.
- * In this case (see unix_create1()) we set artificial
- * negative inflight counter to close race window.
- * It is trick of course and dirty one.
- */
- if (s->sk_socket && s->sk_socket->file)
- open_count = file_count(s->sk_socket->file);
- if (open_count > atomic_read(&unix_sk(s)->inflight))
- maybe_unmark_and_push(s);
- }
+ list_for_each_entry(u, &gc_candidates, link)
+ scan_children(&u->sk, dec_inflight, NULL);
/*
- * Mark phase
+ * Restore the references for children of all candidates,
+ * which have remaining references. Do this recursively, so
+ * only those remain, which form cyclic references.
+ *
+ * Use a "cursor" link, to make the list traversal safe, even
+ * though elements might be moved about.
*/
+ list_add(&cursor, &gc_candidates);
+ while (cursor.next != &gc_candidates) {
+ u = list_entry(cursor.next, struct unix_sock, link);
- while (!empty_stack())
- {
- struct sock *x = pop_stack();
- struct sock *sk;
-
- spin_lock(&x->sk_receive_queue.lock);
- skb = skb_peek(&x->sk_receive_queue);
-
- /*
- * Loop through all but first born
- */
+ /* Move cursor to after the current position. */
+ list_move(&cursor, &u->link);
- while (skb && skb != (struct sk_buff *)&x->sk_receive_queue) {
- /*
- * Do we have file descriptors ?
- */
- if(UNIXCB(skb).fp)
- {
- /*
- * Process the descriptors of this socket
- */
- int nfd=UNIXCB(skb).fp->count;
- struct file **fp = UNIXCB(skb).fp->fp;
- while(nfd--)
- {
- /*
- * Get the socket the fd matches if
- * it indeed does so
- */
- if((sk=unix_get_socket(*fp++))!=NULL)
- {
- maybe_unmark_and_push(sk);
- }
- }
- }
- /* We have to scan not-yet-accepted ones too */
- if (x->sk_state == TCP_LISTEN)
- maybe_unmark_and_push(skb->sk);
- skb=skb->next;
+ if (atomic_read(&u->inflight) > 0) {
+ list_move_tail(&u->link, &gc_inflight_list);
+ u->gc_candidate = 0;
+ scan_children(&u->sk, inc_inflight_move_tail, NULL);
}
- spin_unlock(&x->sk_receive_queue.lock);
- sock_put(x);
}
+ list_del(&cursor);
+ /*
+ * Now gc_candidates contains only garbage. Restore original
+ * inflight counters for these as well, and remove the skbuffs
+ * which are creating the cycle(s).
+ */
skb_queue_head_init(&hitlist);
+ list_for_each_entry(u, &gc_candidates, link)
+ scan_children(&u->sk, inc_inflight, &hitlist);
- forall_unix_sockets(i, s)
- {
- struct unix_sock *u = unix_sk(s);
+ spin_unlock(&unix_gc_lock);
- if (u->gc_tree == GC_ORPHAN) {
- struct sk_buff *nextsk;
+ /* Here we are. Hitlist is filled. Die. */
+ __skb_queue_purge(&hitlist);
- spin_lock(&s->sk_receive_queue.lock);
- skb = skb_peek(&s->sk_receive_queue);
- while (skb &&
- skb != (struct sk_buff *)&s->sk_receive_queue) {
- nextsk = skb->next;
- /*
- * Do we have file descriptors ?
- */
- if (UNIXCB(skb).fp) {
- __skb_unlink(skb,
- &s->sk_receive_queue);
- __skb_queue_tail(&hitlist, skb);
- }
- skb = nextsk;
- }
- spin_unlock(&s->sk_receive_queue.lock);
- }
- u->gc_tree = GC_ORPHAN;
- }
- spin_unlock(&unix_table_lock);
+ spin_lock(&unix_gc_lock);
- /*
- * Here we are. Hitlist is filled. Die.
- */
+ /* All candidates should have been detached by now. */
+ BUG_ON(!list_empty(&gc_candidates));
+ gc_in_progress = false;
- __skb_queue_purge(&hitlist);
- mutex_unlock(&unix_gc_sem);
+ out:
+ spin_unlock(&unix_gc_lock);
}
git.openpandora.org / pandora-kernel.git / blobdiff