--- /dev/null
+/*
+ * NET3: Garbage Collector For AF_UNIX sockets
+ *
+ * Garbage Collector:
+ * Copyright (C) Barak A. Pearlmutter.
+ * Released under the GPL version 2 or later.
+ *
+ * Chopped about by Alan Cox 22/3/96 to make it fit the AF_UNIX socket problem.
+ * If it doesn't work blame me, it worked when Barak sent it.
+ *
+ * Assumptions:
+ *
+ * - object w/ a bit
+ * - free list
+ *
+ * Current optimizations:
+ *
+ * - explicit stack instead of recursion
+ * - tail recurse on first born instead of immediate push/pop
+ * - we gather the stuff that should not be killed into tree
+ * and stack is just a path from root to the current pointer.
+ *
+ * Future optimizations:
+ *
+ * - don't just push entire root set; process in place
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ *
+ * Fixes:
+ * Alan Cox 07 Sept 1997 Vmalloc internal stack as needed.
+ * Cope with changing max_files.
+ * Al Viro 11 Oct 1998
+ * Graph may have cycles. That is, we can send the descriptor
+ * of foo to bar and vice versa. Current code chokes on that.
+ * Fix: move SCM_RIGHTS ones into the separate list and then
+ * skb_free() them all instead of doing explicit fput's.
+ * Another problem: since fput() may block somebody may
+ * create a new unix_socket when we are in the middle of sweep
+ * phase. Fix: revert the logic wrt MARKED. Mark everything
+ * upon the beginning and unmark non-junk ones.
+ *
+ * [12 Oct 1998] AAARGH! New code purges all SCM_RIGHTS
+ * sent to connect()'ed but still not accept()'ed sockets.
+ * Fixed. Old code had slightly different problem here:
+ * extra fput() in situation when we passed the descriptor via
+ * such socket and closed it (descriptor). That would happen on
+ * each unix_gc() until the accept(). Since the struct file in
+ * question would go to the free list and might be reused...
+ * That might be the reason of random oopses on filp_close()
+ * in unrelated processes.
+ *
+ * AV 28 Feb 1999
+ * Kill the explicit allocation of stack. Now we keep the tree
+ * with root in dummy + pointer (gc_current) to one of the nodes.
+ * Stack is represented as path from gc_current to dummy. Unmark
+ * now means "add to tree". Push == "make it a son of gc_current".
+ * Pop == "move gc_current to parent". We keep only pointers to
+ * parents (->gc_tree).
+ * 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>
+#include <linux/string.h>
+#include <linux/socket.h>
+#include <linux/un.h>
+#include <linux/net.h>
+#include <linux/fs.h>
+#include <linux/skbuff.h>
+#include <linux/netdevice.h>
+#include <linux/file.h>
+#include <linux/proc_fs.h>
+#include <linux/mutex.h>
+#include <linux/wait.h>
+
+#include <net/sock.h>
+#include <net/af_unix.h>
+#include <net/scm.h>
+#include <net/tcp_states.h>
+
+/* Internal data structures and random procedures: */
+
+static LIST_HEAD(gc_inflight_list);
+static LIST_HEAD(gc_candidates);
+static DEFINE_SPINLOCK(unix_gc_lock);
+static DECLARE_WAIT_QUEUE_HEAD(unix_gc_wait);
+
+unsigned int unix_tot_inflight;
+
+struct sock *unix_get_socket(struct file *filp)
+{
+ struct sock *u_sock = NULL;
+ struct inode *inode = file_inode(filp);
+
+ /* Socket ? */
+ if (S_ISSOCK(inode->i_mode) && !(filp->f_mode & FMODE_PATH)) {
+ struct socket *sock = SOCKET_I(inode);
+ struct sock *s = sock->sk;
+
+ /* PF_UNIX ? */
+ if (s && sock->ops && sock->ops->family == PF_UNIX)
+ u_sock = s;
+ }
+ return u_sock;
+}
+
+/* Keep the number of times in flight count for the file
+ * descriptor if it is for an AF_UNIX socket.
+ */
+
+void unix_inflight(struct file *fp)
+{
+ struct sock *s = unix_get_socket(fp);
+
+ if (s) {
+ struct unix_sock *u = unix_sk(s);
+
+ spin_lock(&unix_gc_lock);
+
+ if (atomic_long_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));
+ }
+ unix_tot_inflight++;
+ spin_unlock(&unix_gc_lock);
+ }
+}
+
+void unix_notinflight(struct file *fp)
+{
+ struct sock *s = unix_get_socket(fp);
+
+ if (s) {
+ struct unix_sock *u = unix_sk(s);
+
+ spin_lock(&unix_gc_lock);
+ BUG_ON(list_empty(&u->link));
+
+ if (atomic_long_dec_and_test(&u->inflight))
+ list_del_init(&u->link);
+ unix_tot_inflight--;
+ spin_unlock(&unix_gc_lock);
+ }
+}
+
+static void scan_inflight(struct sock *x, void (*func)(struct unix_sock *),
+ struct sk_buff_head *hitlist)
+{
+ struct sk_buff *skb;
+ struct sk_buff *next;
+
+ spin_lock(&x->sk_receive_queue.lock);
+ skb_queue_walk_safe(&x->sk_receive_queue, skb, next) {
+ /* 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) {
+ struct unix_sock *u = unix_sk(sk);
+
+ /* Ignore non-candidates, they could
+ * have been added to the queues after
+ * starting the garbage collection
+ */
+ if (test_bit(UNIX_GC_CANDIDATE, &u->gc_flags)) {
+ hit = true;
+
+ func(u);
+ }
+ }
+ }
+ if (hit && hitlist != NULL) {
+ __skb_unlink(skb, &x->sk_receive_queue);
+ __skb_queue_tail(hitlist, skb);
+ }
+ }
+ }
+ spin_unlock(&x->sk_receive_queue.lock);
+}
+
+static void scan_children(struct sock *x, void (*func)(struct unix_sock *),
+ struct sk_buff_head *hitlist)
+{
+ 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);
+ skb_queue_walk_safe(&x->sk_receive_queue, skb, next) {
+ 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 dec_inflight(struct unix_sock *usk)
+{
+ atomic_long_dec(&usk->inflight);
+}
+
+static void inc_inflight(struct unix_sock *usk)
+{
+ atomic_long_inc(&usk->inflight);
+}
+
+static void inc_inflight_move_tail(struct unix_sock *u)
+{
+ atomic_long_inc(&u->inflight);
+ /* If this still might be part of a cycle, move it to the end
+ * of the list, so that it's checked even if it was already
+ * passed over
+ */
+ if (test_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags))
+ list_move_tail(&u->link, &gc_candidates);
+}
+
+static bool gc_in_progress;
+#define UNIX_INFLIGHT_TRIGGER_GC 16000
+
+void wait_for_unix_gc(void)
+{
+ /* If number of inflight sockets is insane,
+ * force a garbage collect right now.
+ */
+ if (unix_tot_inflight > UNIX_INFLIGHT_TRIGGER_GC && !gc_in_progress)
+ unix_gc();
+ wait_event(unix_gc_wait, gc_in_progress == false);
+}
+
+/* The external entry point: unix_gc() */
+void unix_gc(void)
+{
+ struct unix_sock *u;
+ struct unix_sock *next;
+ struct sk_buff_head hitlist;
+ struct list_head cursor;
+ LIST_HEAD(not_cycle_list);
+
+ spin_lock(&unix_gc_lock);
+
+ /* Avoid a recursive GC. */
+ if (gc_in_progress)
+ goto out;
+
+ gc_in_progress = true;
+ /* 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. Since there are no possible receivers, all
+ * buffers currently on the candidates' queues stay there
+ * during the garbage collection.
+ *
+ * We also know that no new candidate can be added onto the
+ * receive queues. Other, non candidate sockets _can_ be
+ * added to queue, so we must make sure only to touch
+ * candidates.
+ */
+ list_for_each_entry_safe(u, next, &gc_inflight_list, link) {
+ long total_refs;
+ long inflight_refs;
+
+ total_refs = file_count(u->sk.sk_socket->file);
+ inflight_refs = atomic_long_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);
+ __set_bit(UNIX_GC_CANDIDATE, &u->gc_flags);
+ __set_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags);
+ }
+ }
+
+ /* Now remove all internal in-flight reference to children of
+ * the candidates.
+ */
+ list_for_each_entry(u, &gc_candidates, link)
+ scan_children(&u->sk, dec_inflight, NULL);
+
+ /* 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);
+
+ /* Move cursor to after the current position. */
+ list_move(&cursor, &u->link);
+
+ if (atomic_long_read(&u->inflight) > 0) {
+ list_move_tail(&u->link, ¬_cycle_list);
+ __clear_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags);
+ scan_children(&u->sk, inc_inflight_move_tail, NULL);
+ }
+ }
+ list_del(&cursor);
+
+ /* not_cycle_list contains those sockets which do not make up a
+ * cycle. Restore these to the inflight list.
+ */
+ while (!list_empty(¬_cycle_list)) {
+ u = list_entry(not_cycle_list.next, struct unix_sock, link);
+ __clear_bit(UNIX_GC_CANDIDATE, &u->gc_flags);
+ list_move_tail(&u->link, &gc_inflight_list);
+ }
+
+ /* 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);
+
+ spin_unlock(&unix_gc_lock);
+
+ /* Here we are. Hitlist is filled. Die. */
+ __skb_queue_purge(&hitlist);
+
+ spin_lock(&unix_gc_lock);
+
+ /* All candidates should have been detached by now. */
+ BUG_ON(!list_empty(&gc_candidates));
+ gc_in_progress = false;
+ wake_up(&unix_gc_wait);
+
+ out:
+ spin_unlock(&unix_gc_lock);
+}
Code Review / kvmfornfv.git / blobdiff