mm, memcg: fix reclaim deadlock with writeback

[linux/fpc-iii.git] / fs / afs / cell.c

/* AFS cell and server record management
 *
 * Copyright (C) 2002, 2017 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * 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.
 */

#include <linux/slab.h>
#include <linux/key.h>
#include <linux/ctype.h>
#include <linux/dns_resolver.h>
#include <linux/sched.h>
#include <linux/inet.h>
#include <linux/namei.h>
#include <keys/rxrpc-type.h>
#include "internal.h"

static unsigned __read_mostly afs_cell_gc_delay = 10;

static void afs_manage_cell(struct work_struct *);

static void afs_dec_cells_outstanding(struct afs_net *net)
{
        if (atomic_dec_and_test(&net->cells_outstanding))
                wake_up_var(&net->cells_outstanding);
}

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

/*
 * Look up and get an activation reference on a cell record under RCU
 * conditions.  The caller must hold the RCU read lock.
 */
struct afs_cell *afs_lookup_cell_rcu(struct afs_net *net,
                                     const char *name, unsigned int namesz)
{
        struct afs_cell *cell = NULL;
        struct rb_node *p;
        int n, seq = 0, ret = 0;

        _enter("%*.*s", namesz, namesz, name);

        if (name && namesz == 0)
                return ERR_PTR(-EINVAL);
        if (namesz > AFS_MAXCELLNAME)
                return ERR_PTR(-ENAMETOOLONG);

        do {
                /* Unfortunately, rbtree walking doesn't give reliable results
                 * under just the RCU read lock, so we have to check for
                 * changes.
                 */
                if (cell)
                        afs_put_cell(net, cell);
                cell = NULL;
                ret = -ENOENT;

                read_seqbegin_or_lock(&net->cells_lock, &seq);

                if (!name) {
                        cell = rcu_dereference_raw(net->ws_cell);
                        if (cell) {
                                afs_get_cell(cell);
                                break;
                        }
                        ret = -EDESTADDRREQ;
                        continue;
                }

                p = rcu_dereference_raw(net->cells.rb_node);
                while (p) {
                        cell = rb_entry(p, struct afs_cell, net_node);

                        n = strncasecmp(cell->name, name,
                                        min_t(size_t, cell->name_len, namesz));
                        if (n == 0)
                                n = cell->name_len - namesz;
                        if (n < 0) {
                                p = rcu_dereference_raw(p->rb_left);
                        } else if (n > 0) {
                                p = rcu_dereference_raw(p->rb_right);
                        } else {
                                if (atomic_inc_not_zero(&cell->usage)) {
                                        ret = 0;
                                        break;
                                }
                                /* We want to repeat the search, this time with
                                 * the lock properly locked.
                                 */
                        }
                        cell = NULL;
                }

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

        done_seqretry(&net->cells_lock, seq);

        return ret == 0 ? cell : ERR_PTR(ret);
}

/*
 * Set up a cell record and fill in its name, VL server address list and
 * allocate an anonymous key
 */
static struct afs_cell *afs_alloc_cell(struct afs_net *net,
                                       const char *name, unsigned int namelen,
                                       const char *vllist)
{
        struct afs_cell *cell;
        int i, ret;

        ASSERT(name);
        if (namelen == 0)
                return ERR_PTR(-EINVAL);
        if (namelen > AFS_MAXCELLNAME) {
                _leave(" = -ENAMETOOLONG");
                return ERR_PTR(-ENAMETOOLONG);
        }
        if (namelen == 5 && memcmp(name, "@cell", 5) == 0)
                return ERR_PTR(-EINVAL);

        _enter("%*.*s,%s", namelen, namelen, name, vllist);

        cell = kzalloc(sizeof(struct afs_cell), GFP_KERNEL);
        if (!cell) {
                _leave(" = -ENOMEM");
                return ERR_PTR(-ENOMEM);
        }

        cell->net = net;
        cell->name_len = namelen;
        for (i = 0; i < namelen; i++)
                cell->name[i] = tolower(name[i]);

        atomic_set(&cell->usage, 2);
        INIT_WORK(&cell->manager, afs_manage_cell);
        cell->flags = ((1 << AFS_CELL_FL_NOT_READY) |
                       (1 << AFS_CELL_FL_NO_LOOKUP_YET));
        INIT_LIST_HEAD(&cell->proc_volumes);
        rwlock_init(&cell->proc_lock);
        rwlock_init(&cell->vl_addrs_lock);

        /* Fill in the VL server list if we were given a list of addresses to
         * use.
         */
        if (vllist) {
                struct afs_addr_list *alist;

                alist = afs_parse_text_addrs(vllist, strlen(vllist), ':',
                                             VL_SERVICE, AFS_VL_PORT);
                if (IS_ERR(alist)) {
                        ret = PTR_ERR(alist);
                        goto parse_failed;
                }

                rcu_assign_pointer(cell->vl_addrs, alist);
                cell->dns_expiry = TIME64_MAX;
        }

        _leave(" = %p", cell);
        return cell;

parse_failed:
        if (ret == -EINVAL)
                printk(KERN_ERR "kAFS: bad VL server IP address\n");
        kfree(cell);
        _leave(" = %d", ret);
        return ERR_PTR(ret);
}

/*
 * afs_lookup_cell - Look up or create a cell record.
 * @net:        The network namespace
 * @name:       The name of the cell.
 * @namesz:     The strlen of the cell name.
 * @vllist:     A colon/comma separated list of numeric IP addresses or NULL.
 * @excl:       T if an error should be given if the cell name already exists.
 *
 * Look up a cell record by name and query the DNS for VL server addresses if
 * needed.  Note that that actual DNS query is punted off to the manager thread
 * so that this function can return immediately if interrupted whilst allowing
 * cell records to be shared even if not yet fully constructed.
 */
struct afs_cell *afs_lookup_cell(struct afs_net *net,
                                 const char *name, unsigned int namesz,
                                 const char *vllist, bool excl)
{
        struct afs_cell *cell, *candidate, *cursor;
        struct rb_node *parent, **pp;
        int ret, n;

        _enter("%s,%s", name, vllist);

        if (!excl) {
                rcu_read_lock();
                cell = afs_lookup_cell_rcu(net, name, namesz);
                rcu_read_unlock();
                if (!IS_ERR(cell))
                        goto wait_for_cell;
        }

        /* Assume we're probably going to create a cell and preallocate and
         * mostly set up a candidate record.  We can then use this to stash the
         * name, the net namespace and VL server addresses.
         *
         * We also want to do this before we hold any locks as it may involve
         * upcalling to userspace to make DNS queries.
         */
        candidate = afs_alloc_cell(net, name, namesz, vllist);
        if (IS_ERR(candidate)) {
                _leave(" = %ld", PTR_ERR(candidate));
                return candidate;
        }

        /* Find the insertion point and check to see if someone else added a
         * cell whilst we were allocating.
         */
        write_seqlock(&net->cells_lock);

        pp = &net->cells.rb_node;
        parent = NULL;
        while (*pp) {
                parent = *pp;
                cursor = rb_entry(parent, struct afs_cell, net_node);

                n = strncasecmp(cursor->name, name,
                                min_t(size_t, cursor->name_len, namesz));
                if (n == 0)
                        n = cursor->name_len - namesz;
                if (n < 0)
                        pp = &(*pp)->rb_left;
                else if (n > 0)
                        pp = &(*pp)->rb_right;
                else
                        goto cell_already_exists;
        }

        cell = candidate;
        candidate = NULL;
        rb_link_node_rcu(&cell->net_node, parent, pp);
        rb_insert_color(&cell->net_node, &net->cells);
        atomic_inc(&net->cells_outstanding);
        write_sequnlock(&net->cells_lock);

        queue_work(afs_wq, &cell->manager);

wait_for_cell:
        _debug("wait_for_cell");
        ret = wait_on_bit(&cell->flags, AFS_CELL_FL_NOT_READY, TASK_INTERRUPTIBLE);
        smp_rmb();

        switch (READ_ONCE(cell->state)) {
        case AFS_CELL_FAILED:
                ret = cell->error;
                goto error;
        default:
                _debug("weird %u %d", cell->state, cell->error);
                goto error;
        case AFS_CELL_ACTIVE:
                break;
        }

        _leave(" = %p [cell]", cell);
        return cell;

cell_already_exists:
        _debug("cell exists");
        cell = cursor;
        if (excl) {
                ret = -EEXIST;
        } else {
                afs_get_cell(cursor);
                ret = 0;
        }
        write_sequnlock(&net->cells_lock);
        kfree(candidate);
        if (ret == 0)
                goto wait_for_cell;
        goto error_noput;
error:
        afs_put_cell(net, cell);
error_noput:
        _leave(" = %d [error]", ret);
        return ERR_PTR(ret);
}

/*
 * set the root cell information
 * - can be called with a module parameter string
 * - can be called from a write to /proc/fs/afs/rootcell
 */
int afs_cell_init(struct afs_net *net, const char *rootcell)
{
        struct afs_cell *old_root, *new_root;
        const char *cp, *vllist;
        size_t len;

        _enter("");

        if (!rootcell) {
                /* module is loaded with no parameters, or built statically.
                 * - in the future we might initialize cell DB here.
                 */
                _leave(" = 0 [no root]");
                return 0;
        }

        cp = strchr(rootcell, ':');
        if (!cp) {
                _debug("kAFS: no VL server IP addresses specified");
                vllist = NULL;
                len = strlen(rootcell);
        } else {
                vllist = cp + 1;
                len = cp - rootcell;
        }

        /* allocate a cell record for the root cell */
        new_root = afs_lookup_cell(net, rootcell, len, vllist, false);
        if (IS_ERR(new_root)) {
                _leave(" = %ld", PTR_ERR(new_root));
                return PTR_ERR(new_root);
        }

        if (!test_and_set_bit(AFS_CELL_FL_NO_GC, &new_root->flags))
                afs_get_cell(new_root);

        /* install the new cell */
        write_seqlock(&net->cells_lock);
        old_root = rcu_access_pointer(net->ws_cell);
        rcu_assign_pointer(net->ws_cell, new_root);
        write_sequnlock(&net->cells_lock);

        afs_put_cell(net, old_root);
        _leave(" = 0");
        return 0;
}

/*
 * Update a cell's VL server address list from the DNS.
 */
static void afs_update_cell(struct afs_cell *cell)
{
        struct afs_addr_list *alist, *old;
        time64_t now, expiry;

        _enter("%s", cell->name);

        alist = afs_dns_query(cell, &expiry);
        if (IS_ERR(alist)) {
                switch (PTR_ERR(alist)) {
                case -ENODATA:
                        /* The DNS said that the cell does not exist */
                        set_bit(AFS_CELL_FL_NOT_FOUND, &cell->flags);
                        clear_bit(AFS_CELL_FL_DNS_FAIL, &cell->flags);
                        cell->dns_expiry = ktime_get_real_seconds() + 61;
                        break;

                case -EAGAIN:
                case -ECONNREFUSED:
                default:
                        set_bit(AFS_CELL_FL_DNS_FAIL, &cell->flags);
                        cell->dns_expiry = ktime_get_real_seconds() + 10;
                        break;
                }

                cell->error = -EDESTADDRREQ;
        } else {
                clear_bit(AFS_CELL_FL_DNS_FAIL, &cell->flags);
                clear_bit(AFS_CELL_FL_NOT_FOUND, &cell->flags);

                /* Exclusion on changing vl_addrs is achieved by a
                 * non-reentrant work item.
                 */
                old = rcu_dereference_protected(cell->vl_addrs, true);
                rcu_assign_pointer(cell->vl_addrs, alist);
                cell->dns_expiry = expiry;

                if (old)
                        afs_put_addrlist(old);
        }

        if (test_and_clear_bit(AFS_CELL_FL_NO_LOOKUP_YET, &cell->flags))
                wake_up_bit(&cell->flags, AFS_CELL_FL_NO_LOOKUP_YET);

        now = ktime_get_real_seconds();
        afs_set_cell_timer(cell->net, cell->dns_expiry - now);
        _leave("");
}

/*
 * Destroy a cell record
 */
static void afs_cell_destroy(struct rcu_head *rcu)
{
        struct afs_cell *cell = container_of(rcu, struct afs_cell, rcu);

        _enter("%p{%s}", cell, cell->name);

        ASSERTCMP(atomic_read(&cell->usage), ==, 0);

        afs_put_addrlist(rcu_access_pointer(cell->vl_addrs));
        key_put(cell->anonymous_key);
        kfree(cell);

        _leave(" [destroyed]");
}

/*
 * Queue the cell manager.
 */
static void afs_queue_cell_manager(struct afs_net *net)
{
        int outstanding = atomic_inc_return(&net->cells_outstanding);

        _enter("%d", outstanding);

        if (!queue_work(afs_wq, &net->cells_manager))
                afs_dec_cells_outstanding(net);
}

/*
 * Cell management timer.  We have an increment on cells_outstanding that we
 * need to pass along to the work item.
 */
void afs_cells_timer(struct timer_list *timer)
{
        struct afs_net *net = container_of(timer, struct afs_net, cells_timer);

        _enter("");
        if (!queue_work(afs_wq, &net->cells_manager))
                afs_dec_cells_outstanding(net);
}

/*
 * Get a reference on a cell record.
 */
struct afs_cell *afs_get_cell(struct afs_cell *cell)
{
        atomic_inc(&cell->usage);
        return cell;
}

/*
 * Drop a reference on a cell record.
 */
void afs_put_cell(struct afs_net *net, struct afs_cell *cell)
{
        time64_t now, expire_delay;

        if (!cell)
                return;

        _enter("%s", cell->name);

        now = ktime_get_real_seconds();
        cell->last_inactive = now;
        expire_delay = 0;
        if (!test_bit(AFS_CELL_FL_DNS_FAIL, &cell->flags) &&
            !test_bit(AFS_CELL_FL_NOT_FOUND, &cell->flags))
                expire_delay = afs_cell_gc_delay;

        if (atomic_dec_return(&cell->usage) > 1)
                return;

        /* 'cell' may now be garbage collected. */
        afs_set_cell_timer(net, expire_delay);
}

/*
 * Allocate a key to use as a placeholder for anonymous user security.
 */
static int afs_alloc_anon_key(struct afs_cell *cell)
{
        struct key *key;
        char keyname[4 + AFS_MAXCELLNAME + 1], *cp, *dp;

        /* Create a key to represent an anonymous user. */
        memcpy(keyname, "afs@", 4);
        dp = keyname + 4;
        cp = cell->name;
        do {
                *dp++ = tolower(*cp);
        } while (*cp++);

        key = rxrpc_get_null_key(keyname);
        if (IS_ERR(key))
                return PTR_ERR(key);

        cell->anonymous_key = key;

        _debug("anon key %p{%x}",
               cell->anonymous_key, key_serial(cell->anonymous_key));
        return 0;
}

/*
 * Activate a cell.
 */
static int afs_activate_cell(struct afs_net *net, struct afs_cell *cell)
{
        struct hlist_node **p;
        struct afs_cell *pcell;
        int ret;

        if (!cell->anonymous_key) {
                ret = afs_alloc_anon_key(cell);
                if (ret < 0)
                        return ret;
        }

#ifdef CONFIG_AFS_FSCACHE
        cell->cache = fscache_acquire_cookie(afs_cache_netfs.primary_index,
                                             &afs_cell_cache_index_def,
                                             cell->name, strlen(cell->name),
                                             NULL, 0,
                                             cell, 0, true);
#endif
        ret = afs_proc_cell_setup(cell);
        if (ret < 0)
                return ret;

        mutex_lock(&net->proc_cells_lock);
        for (p = &net->proc_cells.first; *p; p = &(*p)->next) {
                pcell = hlist_entry(*p, struct afs_cell, proc_link);
                if (strcmp(cell->name, pcell->name) < 0)
                        break;
        }

        cell->proc_link.pprev = p;
        cell->proc_link.next = *p;
        rcu_assign_pointer(*p, &cell->proc_link.next);
        if (cell->proc_link.next)
                cell->proc_link.next->pprev = &cell->proc_link.next;

        afs_dynroot_mkdir(net, cell);
        mutex_unlock(&net->proc_cells_lock);
        return 0;
}

/*
 * Deactivate a cell.
 */
static void afs_deactivate_cell(struct afs_net *net, struct afs_cell *cell)
{
        _enter("%s", cell->name);

        afs_proc_cell_remove(cell);

        mutex_lock(&net->proc_cells_lock);
        hlist_del_rcu(&cell->proc_link);
        afs_dynroot_rmdir(net, cell);
        mutex_unlock(&net->proc_cells_lock);

#ifdef CONFIG_AFS_FSCACHE
        fscache_relinquish_cookie(cell->cache, NULL, false);
        cell->cache = NULL;
#endif

        _leave("");
}

/*
 * Manage a cell record, initialising and destroying it, maintaining its DNS
 * records.
 */
static void afs_manage_cell(struct work_struct *work)
{
        struct afs_cell *cell = container_of(work, struct afs_cell, manager);
        struct afs_net *net = cell->net;
        bool deleted;
        int ret, usage;

        _enter("%s", cell->name);

again:
        _debug("state %u", cell->state);
        switch (cell->state) {
        case AFS_CELL_INACTIVE:
        case AFS_CELL_FAILED:
                write_seqlock(&net->cells_lock);
                usage = 1;
                deleted = atomic_try_cmpxchg_relaxed(&cell->usage, &usage, 0);
                if (deleted)
                        rb_erase(&cell->net_node, &net->cells);
                write_sequnlock(&net->cells_lock);
                if (deleted)
                        goto final_destruction;
                if (cell->state == AFS_CELL_FAILED)
                        goto done;
                cell->state = AFS_CELL_UNSET;
                goto again;

        case AFS_CELL_UNSET:
                cell->state = AFS_CELL_ACTIVATING;
                goto again;

        case AFS_CELL_ACTIVATING:
                ret = afs_activate_cell(net, cell);
                if (ret < 0)
                        goto activation_failed;

                cell->state = AFS_CELL_ACTIVE;
                smp_wmb();
                clear_bit(AFS_CELL_FL_NOT_READY, &cell->flags);
                wake_up_bit(&cell->flags, AFS_CELL_FL_NOT_READY);
                goto again;

        case AFS_CELL_ACTIVE:
                if (atomic_read(&cell->usage) > 1) {
                        time64_t now = ktime_get_real_seconds();
                        if (cell->dns_expiry <= now && net->live)
                                afs_update_cell(cell);
                        goto done;
                }
                cell->state = AFS_CELL_DEACTIVATING;
                goto again;

        case AFS_CELL_DEACTIVATING:
                set_bit(AFS_CELL_FL_NOT_READY, &cell->flags);
                if (atomic_read(&cell->usage) > 1)
                        goto reverse_deactivation;
                afs_deactivate_cell(net, cell);
                cell->state = AFS_CELL_INACTIVE;
                goto again;

        default:
                break;
        }
        _debug("bad state %u", cell->state);
        BUG(); /* Unhandled state */

activation_failed:
        cell->error = ret;
        afs_deactivate_cell(net, cell);

        cell->state = AFS_CELL_FAILED;
        smp_wmb();
        if (test_and_clear_bit(AFS_CELL_FL_NOT_READY, &cell->flags))
                wake_up_bit(&cell->flags, AFS_CELL_FL_NOT_READY);
        goto again;

reverse_deactivation:
        cell->state = AFS_CELL_ACTIVE;
        smp_wmb();
        clear_bit(AFS_CELL_FL_NOT_READY, &cell->flags);
        wake_up_bit(&cell->flags, AFS_CELL_FL_NOT_READY);
        _leave(" [deact->act]");
        return;

done:
        _leave(" [done %u]", cell->state);
        return;

final_destruction:
        call_rcu(&cell->rcu, afs_cell_destroy);
        afs_dec_cells_outstanding(net);
        _leave(" [destruct %d]", atomic_read(&net->cells_outstanding));
}

/*
 * Manage the records of cells known to a network namespace.  This includes
 * updating the DNS records and garbage collecting unused cells that were
 * automatically added.
 *
 * Note that constructed cell records may only be removed from net->cells by
 * this work item, so it is safe for this work item to stash a cursor pointing
 * into the tree and then return to caller (provided it skips cells that are
 * still under construction).
 *
 * Note also that we were given an increment on net->cells_outstanding by
 * whoever queued us that we need to deal with before returning.
 */
void afs_manage_cells(struct work_struct *work)
{
        struct afs_net *net = container_of(work, struct afs_net, cells_manager);
        struct rb_node *cursor;
        time64_t now = ktime_get_real_seconds(), next_manage = TIME64_MAX;
        bool purging = !net->live;

        _enter("");

        /* Trawl the cell database looking for cells that have expired from
         * lack of use and cells whose DNS results have expired and dispatch
         * their managers.
         */
        read_seqlock_excl(&net->cells_lock);

        for (cursor = rb_first(&net->cells); cursor; cursor = rb_next(cursor)) {
                struct afs_cell *cell =
                        rb_entry(cursor, struct afs_cell, net_node);
                unsigned usage;
                bool sched_cell = false;

                usage = atomic_read(&cell->usage);
                _debug("manage %s %u", cell->name, usage);

                ASSERTCMP(usage, >=, 1);

                if (purging) {
                        if (test_and_clear_bit(AFS_CELL_FL_NO_GC, &cell->flags))
                                usage = atomic_dec_return(&cell->usage);
                        ASSERTCMP(usage, ==, 1);
                }

                if (usage == 1) {
                        time64_t expire_at = cell->last_inactive;

                        if (!test_bit(AFS_CELL_FL_DNS_FAIL, &cell->flags) &&
                            !test_bit(AFS_CELL_FL_NOT_FOUND, &cell->flags))
                                expire_at += afs_cell_gc_delay;
                        if (purging || expire_at <= now)
                                sched_cell = true;
                        else if (expire_at < next_manage)
                                next_manage = expire_at;
                }

                if (!purging) {
                        if (cell->dns_expiry <= now)
                                sched_cell = true;
                        else if (cell->dns_expiry <= next_manage)
                                next_manage = cell->dns_expiry;
                }

                if (sched_cell)
                        queue_work(afs_wq, &cell->manager);
        }

        read_sequnlock_excl(&net->cells_lock);

        /* Update the timer on the way out.  We have to pass an increment on
         * cells_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->cells_manager))
                                atomic_inc(&net->cells_outstanding);
                } else {
                        afs_set_cell_timer(net, next_manage - now);
                }
        }

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

/*
 * Purge in-memory cell database.
 */
void afs_cell_purge(struct afs_net *net)
{
        struct afs_cell *ws;

        _enter("");

        write_seqlock(&net->cells_lock);
        ws = rcu_access_pointer(net->ws_cell);
        RCU_INIT_POINTER(net->ws_cell, NULL);
        write_sequnlock(&net->cells_lock);
        afs_put_cell(net, ws);

        _debug("del timer");
        if (del_timer_sync(&net->cells_timer))
                atomic_dec(&net->cells_outstanding);

        _debug("kick mgr");
        afs_queue_cell_manager(net);

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