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![Thomas Gleixner](/assets/img/avatar_default.png)
Based on 1 normalized pattern(s): released under the gpl version 2 or later and 1 additional normalized pattern(s): 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 extracted by the scancode license scanner the SPDX license identifier GPL-2.0-or-later has been chosen to replace the boilerplate/reference in 1 file(s). Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Allison Randal <allison@lohutok.net> Reviewed-by: Richard Fontana <rfontana@redhat.com> Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org> Cc: linux-spdx@vger.kernel.org Link: https://lkml.kernel.org/r/20190520071858.828691433@linutronix.de Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
307 lines
8.9 KiB
C
307 lines
8.9 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* NET3: Garbage Collector For AF_UNIX sockets
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*
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* Garbage Collector:
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* Copyright (C) Barak A. Pearlmutter.
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*
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* Chopped about by Alan Cox 22/3/96 to make it fit the AF_UNIX socket problem.
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* If it doesn't work blame me, it worked when Barak sent it.
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*
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* Assumptions:
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*
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* - object w/ a bit
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* - free list
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*
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* Current optimizations:
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*
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* - explicit stack instead of recursion
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* - tail recurse on first born instead of immediate push/pop
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* - we gather the stuff that should not be killed into tree
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* and stack is just a path from root to the current pointer.
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*
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* Future optimizations:
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*
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* - don't just push entire root set; process in place
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*
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* Fixes:
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* Alan Cox 07 Sept 1997 Vmalloc internal stack as needed.
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* Cope with changing max_files.
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* Al Viro 11 Oct 1998
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* Graph may have cycles. That is, we can send the descriptor
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* of foo to bar and vice versa. Current code chokes on that.
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* Fix: move SCM_RIGHTS ones into the separate list and then
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* skb_free() them all instead of doing explicit fput's.
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* Another problem: since fput() may block somebody may
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* create a new unix_socket when we are in the middle of sweep
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* phase. Fix: revert the logic wrt MARKED. Mark everything
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* upon the beginning and unmark non-junk ones.
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*
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* [12 Oct 1998] AAARGH! New code purges all SCM_RIGHTS
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* sent to connect()'ed but still not accept()'ed sockets.
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* Fixed. Old code had slightly different problem here:
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* extra fput() in situation when we passed the descriptor via
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* such socket and closed it (descriptor). That would happen on
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* each unix_gc() until the accept(). Since the struct file in
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* question would go to the free list and might be reused...
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* That might be the reason of random oopses on filp_close()
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* in unrelated processes.
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*
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* AV 28 Feb 1999
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* Kill the explicit allocation of stack. Now we keep the tree
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* with root in dummy + pointer (gc_current) to one of the nodes.
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* Stack is represented as path from gc_current to dummy. Unmark
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* now means "add to tree". Push == "make it a son of gc_current".
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* Pop == "move gc_current to parent". We keep only pointers to
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* parents (->gc_tree).
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* AV 1 Mar 1999
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* Damn. Added missing check for ->dead in listen queues scanning.
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*
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* Miklos Szeredi 25 Jun 2007
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* Reimplement with a cycle collecting algorithm. This should
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* solve several problems with the previous code, like being racy
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* wrt receive and holding up unrelated socket operations.
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*/
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#include <linux/kernel.h>
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#include <linux/string.h>
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#include <linux/socket.h>
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#include <linux/un.h>
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#include <linux/net.h>
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#include <linux/fs.h>
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#include <linux/skbuff.h>
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#include <linux/netdevice.h>
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#include <linux/file.h>
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#include <linux/proc_fs.h>
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#include <linux/mutex.h>
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#include <linux/wait.h>
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#include <net/sock.h>
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#include <net/af_unix.h>
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#include <net/scm.h>
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#include <net/tcp_states.h>
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#include "scm.h"
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/* Internal data structures and random procedures: */
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static LIST_HEAD(gc_candidates);
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static DECLARE_WAIT_QUEUE_HEAD(unix_gc_wait);
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static void scan_inflight(struct sock *x, void (*func)(struct unix_sock *),
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struct sk_buff_head *hitlist)
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{
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struct sk_buff *skb;
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struct sk_buff *next;
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spin_lock(&x->sk_receive_queue.lock);
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skb_queue_walk_safe(&x->sk_receive_queue, skb, next) {
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/* Do we have file descriptors ? */
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if (UNIXCB(skb).fp) {
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bool hit = false;
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/* Process the descriptors of this socket */
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int nfd = UNIXCB(skb).fp->count;
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struct file **fp = UNIXCB(skb).fp->fp;
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while (nfd--) {
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/* Get the socket the fd matches if it indeed does so */
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struct sock *sk = unix_get_socket(*fp++);
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if (sk) {
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struct unix_sock *u = unix_sk(sk);
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/* Ignore non-candidates, they could
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* have been added to the queues after
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* starting the garbage collection
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*/
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if (test_bit(UNIX_GC_CANDIDATE, &u->gc_flags)) {
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hit = true;
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func(u);
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}
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}
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}
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if (hit && hitlist != NULL) {
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__skb_unlink(skb, &x->sk_receive_queue);
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__skb_queue_tail(hitlist, skb);
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}
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}
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}
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spin_unlock(&x->sk_receive_queue.lock);
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}
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static void scan_children(struct sock *x, void (*func)(struct unix_sock *),
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struct sk_buff_head *hitlist)
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{
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if (x->sk_state != TCP_LISTEN) {
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scan_inflight(x, func, hitlist);
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} else {
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struct sk_buff *skb;
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struct sk_buff *next;
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struct unix_sock *u;
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LIST_HEAD(embryos);
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/* For a listening socket collect the queued embryos
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* and perform a scan on them as well.
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*/
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spin_lock(&x->sk_receive_queue.lock);
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skb_queue_walk_safe(&x->sk_receive_queue, skb, next) {
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u = unix_sk(skb->sk);
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/* An embryo cannot be in-flight, so it's safe
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* to use the list link.
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*/
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BUG_ON(!list_empty(&u->link));
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list_add_tail(&u->link, &embryos);
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}
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spin_unlock(&x->sk_receive_queue.lock);
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while (!list_empty(&embryos)) {
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u = list_entry(embryos.next, struct unix_sock, link);
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scan_inflight(&u->sk, func, hitlist);
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list_del_init(&u->link);
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}
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}
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}
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static void dec_inflight(struct unix_sock *usk)
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{
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atomic_long_dec(&usk->inflight);
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}
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static void inc_inflight(struct unix_sock *usk)
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{
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atomic_long_inc(&usk->inflight);
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}
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static void inc_inflight_move_tail(struct unix_sock *u)
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{
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atomic_long_inc(&u->inflight);
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/* If this still might be part of a cycle, move it to the end
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* of the list, so that it's checked even if it was already
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* passed over
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*/
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if (test_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags))
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list_move_tail(&u->link, &gc_candidates);
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}
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static bool gc_in_progress;
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#define UNIX_INFLIGHT_TRIGGER_GC 16000
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void wait_for_unix_gc(void)
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{
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/* If number of inflight sockets is insane,
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* force a garbage collect right now.
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*/
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if (unix_tot_inflight > UNIX_INFLIGHT_TRIGGER_GC && !gc_in_progress)
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unix_gc();
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wait_event(unix_gc_wait, gc_in_progress == false);
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}
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/* The external entry point: unix_gc() */
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void unix_gc(void)
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{
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struct unix_sock *u;
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struct unix_sock *next;
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struct sk_buff_head hitlist;
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struct list_head cursor;
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LIST_HEAD(not_cycle_list);
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spin_lock(&unix_gc_lock);
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/* Avoid a recursive GC. */
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if (gc_in_progress)
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goto out;
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gc_in_progress = true;
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/* First, select candidates for garbage collection. Only
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* in-flight sockets are considered, and from those only ones
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* which don't have any external reference.
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*
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* Holding unix_gc_lock will protect these candidates from
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* being detached, and hence from gaining an external
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* reference. Since there are no possible receivers, all
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* buffers currently on the candidates' queues stay there
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* during the garbage collection.
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*
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* We also know that no new candidate can be added onto the
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* receive queues. Other, non candidate sockets _can_ be
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* added to queue, so we must make sure only to touch
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* candidates.
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*/
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list_for_each_entry_safe(u, next, &gc_inflight_list, link) {
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long total_refs;
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long inflight_refs;
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total_refs = file_count(u->sk.sk_socket->file);
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inflight_refs = atomic_long_read(&u->inflight);
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BUG_ON(inflight_refs < 1);
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BUG_ON(total_refs < inflight_refs);
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if (total_refs == inflight_refs) {
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list_move_tail(&u->link, &gc_candidates);
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__set_bit(UNIX_GC_CANDIDATE, &u->gc_flags);
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__set_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags);
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}
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}
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/* Now remove all internal in-flight reference to children of
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* the candidates.
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*/
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list_for_each_entry(u, &gc_candidates, link)
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scan_children(&u->sk, dec_inflight, NULL);
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/* Restore the references for children of all candidates,
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* which have remaining references. Do this recursively, so
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* only those remain, which form cyclic references.
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*
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* Use a "cursor" link, to make the list traversal safe, even
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* though elements might be moved about.
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*/
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list_add(&cursor, &gc_candidates);
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while (cursor.next != &gc_candidates) {
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u = list_entry(cursor.next, struct unix_sock, link);
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/* Move cursor to after the current position. */
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list_move(&cursor, &u->link);
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if (atomic_long_read(&u->inflight) > 0) {
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list_move_tail(&u->link, ¬_cycle_list);
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__clear_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags);
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scan_children(&u->sk, inc_inflight_move_tail, NULL);
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}
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}
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list_del(&cursor);
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/* Now gc_candidates contains only garbage. Restore original
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* inflight counters for these as well, and remove the skbuffs
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* which are creating the cycle(s).
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*/
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skb_queue_head_init(&hitlist);
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list_for_each_entry(u, &gc_candidates, link)
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scan_children(&u->sk, inc_inflight, &hitlist);
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/* not_cycle_list contains those sockets which do not make up a
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* cycle. Restore these to the inflight list.
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*/
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while (!list_empty(¬_cycle_list)) {
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u = list_entry(not_cycle_list.next, struct unix_sock, link);
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__clear_bit(UNIX_GC_CANDIDATE, &u->gc_flags);
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list_move_tail(&u->link, &gc_inflight_list);
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}
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spin_unlock(&unix_gc_lock);
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/* Here we are. Hitlist is filled. Die. */
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__skb_queue_purge(&hitlist);
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spin_lock(&unix_gc_lock);
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/* All candidates should have been detached by now. */
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BUG_ON(!list_empty(&gc_candidates));
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gc_in_progress = false;
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wake_up(&unix_gc_wait);
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out:
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spin_unlock(&unix_gc_lock);
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}
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