linux/fs/afs/server.c

// SPDX-License-Identifier: GPL-2.0-or-later
/* AFS server record management
 *
 * Copyright (C) 2002, 2007 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#include <linux/sched.h>
#include <linux/slab.h>
#include "afs_fs.h"
#include "internal.h"
#include "protocol_yfs.h"

static unsigned afs_server_gc_delay = 10;	/* Server record timeout in seconds */
static atomic_t afs_server_debug_id;

static struct afs_server *afs_maybe_use_server(struct afs_server *,
					       enum afs_server_trace);
static void __afs_put_server(struct afs_net *, struct afs_server *);

/*
 * Find a server by one of its addresses.
 */
struct afs_server *afs_find_server(struct afs_net *net, const struct rxrpc_peer *peer)
{
	const struct afs_addr_list *alist;
	struct afs_server *server = NULL;
	unsigned int i;
	int seq = 1;

	rcu_read_lock();

	do {
		if (server)
			afs_unuse_server_notime(net, server, afs_server_trace_put_find_rsq);
		server = NULL;
		seq++; /* 2 on the 1st/lockless path, otherwise odd */
		read_seqbegin_or_lock(&net->fs_addr_lock, &seq);

		hlist_for_each_entry_rcu(server, &net->fs_addresses6, addr6_link) {
			alist = rcu_dereference(server->addresses);
			for (i = 0; i < alist->nr_addrs; i++)
				if (alist->addrs[i].peer == peer)
					goto found;
		}

		server = NULL;
		continue;
	found:
		server = afs_maybe_use_server(server, afs_server_trace_get_by_addr);

	} while (need_seqretry(&net->fs_addr_lock, seq));

	done_seqretry(&net->fs_addr_lock, seq);

	rcu_read_unlock();
	return server;
}

/*
 * Look up a server by its UUID and mark it active.
 */
struct afs_server *afs_find_server_by_uuid(struct afs_net *net, const uuid_t *uuid)
{
	struct afs_server *server = NULL;
	struct rb_node *p;
	int diff, seq = 1;

	_enter("%pU", uuid);

	do {
		/* Unfortunately, rbtree walking doesn't give reliable results
		 * under just the RCU read lock, so we have to check for
		 * changes.
		 */
		if (server)
			afs_unuse_server(net, server, afs_server_trace_put_uuid_rsq);
		server = NULL;
		seq++; /* 2 on the 1st/lockless path, otherwise odd */
		read_seqbegin_or_lock(&net->fs_lock, &seq);

		p = net->fs_servers.rb_node;
		while (p) {
			server = rb_entry(p, struct afs_server, uuid_rb);

			diff = memcmp(uuid, &server->uuid, sizeof(*uuid));
			if (diff < 0) {
				p = p->rb_left;
			} else if (diff > 0) {
				p = p->rb_right;
			} else {
				afs_use_server(server, afs_server_trace_get_by_uuid);
				break;
			}

			server = NULL;
		}
	} while (need_seqretry(&net->fs_lock, seq));

	done_seqretry(&net->fs_lock, seq);

	_leave(" = %p", server);
	return server;
}

/*
 * Install a server record in the namespace tree.  If there's a clash, we stick
 * it into a list anchored on whichever afs_server struct is actually in the
 * tree.
 */
static struct afs_server *afs_install_server(struct afs_cell *cell,
					     struct afs_server *candidate)
{
	const struct afs_addr_list *alist;
	struct afs_server *server, *next;
	struct afs_net *net = cell->net;
	struct rb_node **pp, *p;
	int diff;

	_enter("%p", candidate);

	write_seqlock(&net->fs_lock);

	/* Firstly install the server in the UUID lookup tree */
	pp = &net->fs_servers.rb_node;
	p = NULL;
	while (*pp) {
		p = *pp;
		_debug("- consider %p", p);
		server = rb_entry(p, struct afs_server, uuid_rb);
		diff = memcmp(&candidate->uuid, &server->uuid, sizeof(uuid_t));
		if (diff < 0) {
			pp = &(*pp)->rb_left;
		} else if (diff > 0) {
			pp = &(*pp)->rb_right;
		} else {
			if (server->cell == cell)
				goto exists;

			/* We have the same UUID representing servers in
			 * different cells.  Append the new server to the list.
			 */
			for (;;) {
				next = rcu_dereference_protected(
					server->uuid_next,
					lockdep_is_held(&net->fs_lock.lock));
				if (!next)
					break;
				server = next;
			}
			rcu_assign_pointer(server->uuid_next, candidate);
			candidate->uuid_prev = server;
			server = candidate;
			goto added_dup;
		}
	}

	server = candidate;
	rb_link_node(&server->uuid_rb, p, pp);
	rb_insert_color(&server->uuid_rb, &net->fs_servers);
	hlist_add_head_rcu(&server->proc_link, &net->fs_proc);

added_dup:
	write_seqlock(&net->fs_addr_lock);
	alist = rcu_dereference_protected(server->addresses,
					  lockdep_is_held(&net->fs_addr_lock.lock));

	/* Secondly, if the server has any IPv4 and/or IPv6 addresses, install
	 * it in the IPv4 and/or IPv6 reverse-map lists.
	 *
	 * TODO: For speed we want to use something other than a flat list
	 * here; even sorting the list in terms of lowest address would help a
	 * bit, but anything we might want to do gets messy and memory
	 * intensive.
	 */
	if (alist->nr_ipv4 > 0)
		hlist_add_head_rcu(&server->addr4_link, &net->fs_addresses4);
	if (alist->nr_addrs > alist->nr_ipv4)
		hlist_add_head_rcu(&server->addr6_link, &net->fs_addresses6);

	write_sequnlock(&net->fs_addr_lock);

exists:
	afs_get_server(server, afs_server_trace_get_install);
	write_sequnlock(&net->fs_lock);
	return server;
}

/*
 * Allocate a new server record and mark it active.
 */
static struct afs_server *afs_alloc_server(struct afs_cell *cell,
					   const uuid_t *uuid,
					   struct afs_addr_list *alist)
{
	struct afs_server *server;
	struct afs_net *net = cell->net;

	_enter("");

	server = kzalloc(sizeof(struct afs_server), GFP_KERNEL);
	if (!server)
		goto enomem;

	refcount_set(&server->ref, 1);
	atomic_set(&server->active, 1);
	server->debug_id = atomic_inc_return(&afs_server_debug_id);
	RCU_INIT_POINTER(server->addresses, alist);
	server->addr_version = alist->version;
	server->uuid = *uuid;
	rwlock_init(&server->fs_lock);
	INIT_WORK(&server->initcb_work, afs_server_init_callback_work);
	init_waitqueue_head(&server->probe_wq);
	INIT_LIST_HEAD(&server->probe_link);
	spin_lock_init(&server->probe_lock);
	server->cell = cell;
	server->rtt = UINT_MAX;

	afs_inc_servers_outstanding(net);
	trace_afs_server(server->debug_id, 1, 1, afs_server_trace_alloc);
	_leave(" = %p", server);
	return server;

enomem:
	_leave(" = NULL [nomem]");
	return NULL;
}

/*
 * Look up an address record for a server
 */
static struct afs_addr_list *afs_vl_lookup_addrs(struct afs_cell *cell,
						 struct key *key, const uuid_t *uuid)
{
	struct afs_vl_cursor vc;
	struct afs_addr_list *alist = NULL;
	int ret;

	ret = -ERESTARTSYS;
	if (afs_begin_vlserver_operation(&vc, cell, key)) {
		while (afs_select_vlserver(&vc)) {
			if (test_bit(AFS_VLSERVER_FL_IS_YFS, &vc.server->flags))
				alist = afs_yfsvl_get_endpoints(&vc, uuid);
			else
				alist = afs_vl_get_addrs_u(&vc, uuid);
		}

		ret = afs_end_vlserver_operation(&vc);
	}

	return ret < 0 ? ERR_PTR(ret) : alist;
}

/*
 * Get or create a fileserver record.
 */
struct afs_server *afs_lookup_server(struct afs_cell *cell, struct key *key,
				     const uuid_t *uuid, u32 addr_version)
{
	struct afs_addr_list *alist;
	struct afs_server *server, *candidate;

	_enter("%p,%pU", cell->net, uuid);

	server = afs_find_server_by_uuid(cell->net, uuid);
	if (server) {
		if (server->addr_version != addr_version)
			set_bit(AFS_SERVER_FL_NEEDS_UPDATE, &server->flags);
		return server;
	}

	alist = afs_vl_lookup_addrs(cell, key, uuid);
	if (IS_ERR(alist))
		return ERR_CAST(alist);

	candidate = afs_alloc_server(cell, uuid, alist);
	if (!candidate) {
		afs_put_addrlist(alist);
		return ERR_PTR(-ENOMEM);
	}

	server = afs_install_server(cell, candidate);
	if (server != candidate) {
		afs_put_addrlist(alist);
		kfree(candidate);
	} else {
		/* Immediately dispatch an asynchronous probe to each interface
		 * on the fileserver.  This will make sure the repeat-probing
		 * service is started.
		 */
		afs_fs_probe_fileserver(cell->net, server, key, true);
	}

	return server;
}

/*
 * Set the server timer to fire after a given delay, assuming it's not already
 * set for an earlier time.
 */
static void afs_set_server_timer(struct afs_net *net, time64_t delay)
{
	if (net->live) {
		afs_inc_servers_outstanding(net);
		if (timer_reduce(&net->fs_timer, jiffies + delay * HZ))
			afs_dec_servers_outstanding(net);
	}
}

/*
 * Server management timer.  We have an increment on fs_outstanding that we
 * need to pass along to the work item.
 */
void afs_servers_timer(struct timer_list *timer)
{
	struct afs_net *net = container_of(timer, struct afs_net, fs_timer);

	_enter("");
	if (!queue_work(afs_wq, &net->fs_manager))
		afs_dec_servers_outstanding(net);
}

/*
 * Get a reference on a server object.
 */
struct afs_server *afs_get_server(struct afs_server *server,
				  enum afs_server_trace reason)
{
	unsigned int a;
	int r;

	__refcount_inc(&server->ref, &r);
	a = atomic_read(&server->active);
	trace_afs_server(server->debug_id, r + 1, a, reason);
	return server;
}

/*
 * Try to get a reference on a server object.
 */
static struct afs_server *afs_maybe_use_server(struct afs_server *server,
					       enum afs_server_trace reason)
{
	unsigned int a;
	int r;

	if (!__refcount_inc_not_zero(&server->ref, &r))
		return NULL;

	a = atomic_inc_return(&server->active);
	trace_afs_server(server->debug_id, r + 1, a, reason);
	return server;
}

/*
 * Get an active count on a server object.
 */
struct afs_server *afs_use_server(struct afs_server *server, enum afs_server_trace reason)
{
	unsigned int a;
	int r;

	__refcount_inc(&server->ref, &r);
	a = atomic_inc_return(&server->active);

	trace_afs_server(server->debug_id, r + 1, a, reason);
	return server;
}

/*
 * Release a reference on a server record.
 */
void afs_put_server(struct afs_net *net, struct afs_server *server,
		    enum afs_server_trace reason)
{
	unsigned int a, debug_id = server->debug_id;
	bool zero;
	int r;

	if (!server)
		return;

	a = atomic_read(&server->active);
	zero = __refcount_dec_and_test(&server->ref, &r);
	trace_afs_server(debug_id, r - 1, a, reason);
	if (unlikely(zero))
		__afs_put_server(net, server);
}

/*
 * Drop an active count on a server object without updating the last-unused
 * time.
 */
void afs_unuse_server_notime(struct afs_net *net, struct afs_server *server,
			     enum afs_server_trace reason)
{
	if (server) {
		unsigned int active = atomic_dec_return(&server->active);

		if (active == 0)
			afs_set_server_timer(net, afs_server_gc_delay);
		afs_put_server(net, server, reason);
	}
}

/*
 * Drop an active count on a server object.
 */
void afs_unuse_server(struct afs_net *net, struct afs_server *server,
		      enum afs_server_trace reason)
{
	if (server) {
		server->unuse_time = ktime_get_real_seconds();
		afs_unuse_server_notime(net, server, reason);
	}
}

static void afs_server_rcu(struct rcu_head *rcu)
{
	struct afs_server *server = container_of(rcu, struct afs_server, rcu);

	trace_afs_server(server->debug_id, refcount_read(&server->ref),
			 atomic_read(&server->active), afs_server_trace_free);
	afs_put_addrlist(rcu_access_pointer(server->addresses));
	kfree(server);
}

static void __afs_put_server(struct afs_net *net, struct afs_server *server)
{
	call_rcu(&server->rcu, afs_server_rcu);
	afs_dec_servers_outstanding(net);
}

static void afs_give_up_callbacks(struct afs_net *net, struct afs_server *server)
{
	struct afs_addr_list *alist = rcu_access_pointer(server->addresses);
	struct afs_addr_cursor ac = {
		.alist	= alist,
		.index	= alist->preferred,
	};

	afs_fs_give_up_all_callbacks(net, server, &ac, NULL);
}

/*
 * destroy a dead server
 */
static void afs_destroy_server(struct afs_net *net, struct afs_server *server)
{
	if (test_bit(AFS_SERVER_FL_MAY_HAVE_CB, &server->flags))
		afs_give_up_callbacks(net, server);

	flush_work(&server->initcb_work);
	afs_put_server(net, server, afs_server_trace_destroy);
}

/*
 * Garbage collect any expired servers.
 */
static void afs_gc_servers(struct afs_net *net, struct afs_server *gc_list)
{
	struct afs_server *server, *next, *prev;
	int active;

	while ((server = gc_list)) {
		gc_list = server->gc_next;

		write_seqlock(&net->fs_lock);

		active = atomic_read(&server->active);
		if (active == 0) {
			trace_afs_server(server->debug_id, refcount_read(&server->ref),
					 active, afs_server_trace_gc);
			next = rcu_dereference_protected(
				server->uuid_next, lockdep_is_held(&net->fs_lock.lock));
			prev = server->uuid_prev;
			if (!prev) {
				/* The one at the front is in the tree */
				if (!next) {
					rb_erase(&server->uuid_rb, &net->fs_servers);
				} else {
					rb_replace_node_rcu(&server->uuid_rb,
							    &next->uuid_rb,
							    &net->fs_servers);
					next->uuid_prev = NULL;
				}
			} else {
				/* This server is not at the front */
				rcu_assign_pointer(prev->uuid_next, next);
				if (next)
					next->uuid_prev = prev;
			}

			list_del(&server->probe_link);
			hlist_del_rcu(&server->proc_link);
			if (!hlist_unhashed(&server->addr4_link))
				hlist_del_rcu(&server->addr4_link);
			if (!hlist_unhashed(&server->addr6_link))
				hlist_del_rcu(&server->addr6_link);
		}
		write_sequnlock(&net->fs_lock);

		if (active == 0)
			afs_destroy_server(net, server);
	}
}

/*
 * Manage the records of servers known to be within a network namespace.  This
 * includes garbage collecting unused servers.
 *
 * Note also that we were given an increment on net->servers_outstanding by
 * whoever queued us that we need to deal with before returning.
 */
void afs_manage_servers(struct work_struct *work)
{
	struct afs_net *net = container_of(work, struct afs_net, fs_manager);
	struct afs_server *gc_list = NULL;
	struct rb_node *cursor;
	time64_t now = ktime_get_real_seconds(), next_manage = TIME64_MAX;
	bool purging = !net->live;

	_enter("");

	/* Trawl the server list looking for servers that have expired from
	 * lack of use.
	 */
	read_seqlock_excl(&net->fs_lock);

	for (cursor = rb_first(&net->fs_servers); cursor; cursor = rb_next(cursor)) {
		struct afs_server *server =
			rb_entry(cursor, struct afs_server, uuid_rb);
		int active = atomic_read(&server->active);

		_debug("manage %pU %u", &server->uuid, active);

		if (purging) {
			trace_afs_server(server->debug_id, refcount_read(&server->ref),
					 active, afs_server_trace_purging);
			if (active != 0)
				pr_notice("Can't purge s=%08x\n", server->debug_id);
		}

		if (active == 0) {
			time64_t expire_at = server->unuse_time;

			if (!test_bit(AFS_SERVER_FL_VL_FAIL, &server->flags) &&
			    !test_bit(AFS_SERVER_FL_NOT_FOUND, &server->flags))
				expire_at += afs_server_gc_delay;
			if (purging || expire_at <= now) {
				server->gc_next = gc_list;
				gc_list = server;
			} else if (expire_at < next_manage) {
				next_manage = expire_at;
			}
		}
	}

	read_sequnlock_excl(&net->fs_lock);

	/* Update the timer on the way out.  We have to pass an increment on
	 * servers_outstanding in the namespace that we are in to the timer or
	 * the work scheduler.
	 */
	if (!purging && next_manage < TIME64_MAX) {
		now = ktime_get_real_seconds();

		if (next_manage - now <= 0) {
			if (queue_work(afs_wq, &net->fs_manager))
				afs_inc_servers_outstanding(net);
		} else {
			afs_set_server_timer(net, next_manage - now);
		}
	}

	afs_gc_servers(net, gc_list);

	afs_dec_servers_outstanding(net);
	_leave(" [%d]", atomic_read(&net->servers_outstanding));
}

static void afs_queue_server_manager(struct afs_net *net)
{
	afs_inc_servers_outstanding(net);
	if (!queue_work(afs_wq, &net->fs_manager))
		afs_dec_servers_outstanding(net);
}

/*
 * Purge list of servers.
 */
void afs_purge_servers(struct afs_net *net)
{
	_enter("");

	if (del_timer_sync(&net->fs_timer))
		afs_dec_servers_outstanding(net);

	afs_queue_server_manager(net);

	_debug("wait");
	atomic_dec(&net->servers_outstanding);
	wait_var_event(&net->servers_outstanding,
		       !atomic_read(&net->servers_outstanding));
	_leave("");
}

/*
 * Get an update for a server's address list.
 */
static noinline bool afs_update_server_record(struct afs_operation *op,
					      struct afs_server *server)
{
	struct afs_addr_list *alist, *discard;

	_enter("");

	trace_afs_server(server->debug_id, refcount_read(&server->ref),
			 atomic_read(&server->active),
			 afs_server_trace_update);

	alist = afs_vl_lookup_addrs(op->volume->cell, op->key, &server->uuid);
	if (IS_ERR(alist)) {
		if ((PTR_ERR(alist) == -ERESTARTSYS ||
		     PTR_ERR(alist) == -EINTR) &&
		    (op->flags & AFS_OPERATION_UNINTR) &&
		    server->addresses) {
			_leave(" = t [intr]");
			return true;
		}
		afs_op_set_error(op, PTR_ERR(alist));
		_leave(" = f [%d]", afs_op_error(op));
		return false;
	}

	discard = alist;
	if (server->addr_version != alist->version) {
		write_lock(&server->fs_lock);
		discard = rcu_dereference_protected(server->addresses,
						    lockdep_is_held(&server->fs_lock));
		rcu_assign_pointer(server->addresses, alist);
		server->addr_version = alist->version;
		write_unlock(&server->fs_lock);
	}

	afs_put_addrlist(discard);
	_leave(" = t");
	return true;
}

/*
 * See if a server's address list needs updating.
 */
bool afs_check_server_record(struct afs_operation *op, struct afs_server *server)
{
	bool success;
	int ret, retries = 0;

	_enter("");

	ASSERT(server);

retry:
	if (test_bit(AFS_SERVER_FL_UPDATING, &server->flags))
		goto wait;
	if (test_bit(AFS_SERVER_FL_NEEDS_UPDATE, &server->flags))
		goto update;
	_leave(" = t [good]");
	return true;

update:
	if (!test_and_set_bit_lock(AFS_SERVER_FL_UPDATING, &server->flags)) {
		clear_bit(AFS_SERVER_FL_NEEDS_UPDATE, &server->flags);
		success = afs_update_server_record(op, server);
		clear_bit_unlock(AFS_SERVER_FL_UPDATING, &server->flags);
		wake_up_bit(&server->flags, AFS_SERVER_FL_UPDATING);
		_leave(" = %d", success);
		return success;
	}

wait:
	ret = wait_on_bit(&server->flags, AFS_SERVER_FL_UPDATING,
			  (op->flags & AFS_OPERATION_UNINTR) ?
			  TASK_UNINTERRUPTIBLE : TASK_INTERRUPTIBLE);
	if (ret == -ERESTARTSYS) {
		afs_op_set_error(op, ret);
		_leave(" = f [intr]");
		return false;
	}

	retries++;
	if (retries == 4) {
		_leave(" = f [stale]");
		ret = -ESTALE;
		return false;
	}
	goto retry;
}