/* netfs cookie management
 *
 * Copyright (C) 2004-2007 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.
 *
 * See Documentation/filesystems/caching/netfs-api.txt for more information on
 * the netfs API.
 */

#define FSCACHE_DEBUG_LEVEL COOKIE
#include <linux/module.h>
#include <linux/slab.h>
#include "internal.h"

struct kmem_cache *fscache_cookie_jar;

static atomic_t fscache_object_debug_id = ATOMIC_INIT(0);

#define fscache_cookie_hash_shift 15
static struct hlist_bl_head fscache_cookie_hash[1 << fscache_cookie_hash_shift];

static int fscache_acquire_non_index_cookie(struct fscache_cookie *cookie,
                                            loff_t object_size);
static int fscache_alloc_object(struct fscache_cache *cache,
                                struct fscache_cookie *cookie);
static int fscache_attach_object(struct fscache_cookie *cookie,
                                 struct fscache_object *object);

static void fscache_print_cookie(struct fscache_cookie *cookie, char prefix)
{
        struct hlist_node *object;
        const u8 *k;
        unsigned loop;

        pr_err("%c-cookie c=%p [p=%p fl=%lx nc=%u na=%u]\n",
               prefix, cookie, cookie->parent, cookie->flags,
               atomic_read(&cookie->n_children),
               atomic_read(&cookie->n_active));
        pr_err("%c-cookie d=%p n=%p\n",
               prefix, cookie->def, cookie->netfs_data);

        object = READ_ONCE(cookie->backing_objects.first);
        if (object)
                pr_err("%c-cookie o=%p\n",
                       prefix, hlist_entry(object, struct fscache_object, cookie_link));

        pr_err("%c-key=[%u] '", prefix, cookie->key_len);
        k = (cookie->key_len <= sizeof(cookie->inline_key)) ?
                cookie->inline_key : cookie->key;
        for (loop = 0; loop < cookie->key_len; loop++)
                pr_cont("%02x", k[loop]);
        pr_cont("'\n");
}

void fscache_free_cookie(struct fscache_cookie *cookie)
{
        if (cookie) {
                BUG_ON(!hlist_empty(&cookie->backing_objects));
                if (cookie->aux_len > sizeof(cookie->inline_aux))
                        kfree(cookie->aux);
                if (cookie->key_len > sizeof(cookie->inline_key))
                        kfree(cookie->key);
                kmem_cache_free(fscache_cookie_jar, cookie);
        }
}

/*
 * Set the index key in a cookie.  The cookie struct has space for a 16-byte
 * key plus length and hash, but if that's not big enough, it's instead a
 * pointer to a buffer containing 3 bytes of hash, 1 byte of length and then
 * the key data.
 */
static int fscache_set_key(struct fscache_cookie *cookie,
                           const void *index_key, size_t index_key_len)
{
        unsigned long long h;
        u32 *buf;
        int bufs;
        int i;

        bufs = DIV_ROUND_UP(index_key_len, sizeof(*buf));

        if (index_key_len > sizeof(cookie->inline_key)) {
                buf = kcalloc(bufs, sizeof(*buf), GFP_KERNEL);
                if (!buf)
                        return -ENOMEM;
                cookie->key = buf;
        } else {
                buf = (u32 *)cookie->inline_key;
        }

        memcpy(buf, index_key, index_key_len);

        /* Calculate a hash and combine this with the length in the first word
         * or first half word
         */
        h = (unsigned long)cookie->parent;
        h += index_key_len + cookie->type;

        for (i = 0; i < bufs; i++)
                h += buf[i];

        cookie->key_hash = h ^ (h >> 32);
        return 0;
}

static long fscache_compare_cookie(const struct fscache_cookie *a,
                                   const struct fscache_cookie *b)
{
        const void *ka, *kb;

        if (a->key_hash != b->key_hash)
                return (long)a->key_hash - (long)b->key_hash;
        if (a->parent != b->parent)
                return (long)a->parent - (long)b->parent;
        if (a->key_len != b->key_len)
                return (long)a->key_len - (long)b->key_len;
        if (a->type != b->type)
                return (long)a->type - (long)b->type;

        if (a->key_len <= sizeof(a->inline_key)) {
                ka = &a->inline_key;
                kb = &b->inline_key;
        } else {
                ka = a->key;
                kb = b->key;
        }
        return memcmp(ka, kb, a->key_len);
}

/*
 * Allocate a cookie.
 */
struct fscache_cookie *fscache_alloc_cookie(
        struct fscache_cookie *parent,
        const struct fscache_cookie_def *def,
        const void *index_key, size_t index_key_len,
        const void *aux_data, size_t aux_data_len,
        void *netfs_data,
        loff_t object_size)
{
        struct fscache_cookie *cookie;

        /* allocate and initialise a cookie */
        cookie = kmem_cache_zalloc(fscache_cookie_jar, GFP_KERNEL);
        if (!cookie)
                return NULL;

        cookie->key_len = index_key_len;
        cookie->aux_len = aux_data_len;

        if (fscache_set_key(cookie, index_key, index_key_len) < 0)
                goto nomem;

        if (cookie->aux_len <= sizeof(cookie->inline_aux)) {
                memcpy(cookie->inline_aux, aux_data, cookie->aux_len);
        } else {
                cookie->aux = kmemdup(aux_data, cookie->aux_len, GFP_KERNEL);
                if (!cookie->aux)
                        goto nomem;
        }

        atomic_set(&cookie->usage, 1);
        atomic_set(&cookie->n_children, 0);

        /* We keep the active count elevated until relinquishment to prevent an
         * attempt to wake up every time the object operations queue quiesces.
         */
        atomic_set(&cookie->n_active, 1);

        cookie->def             = def;
        cookie->parent          = parent;
        cookie->netfs_data      = netfs_data;
        cookie->flags           = (1 << FSCACHE_COOKIE_NO_DATA_YET);
        cookie->type            = def->type;
        spin_lock_init(&cookie->lock);
        spin_lock_init(&cookie->stores_lock);
        INIT_HLIST_HEAD(&cookie->backing_objects);

        /* radix tree insertion won't use the preallocation pool unless it's
         * told it may not wait */
        INIT_RADIX_TREE(&cookie->stores, GFP_NOFS & ~__GFP_DIRECT_RECLAIM);
        return cookie;

nomem:
        fscache_free_cookie(cookie);
        return NULL;
}

/*
 * Attempt to insert the new cookie into the hash.  If there's a collision, we
 * return the old cookie if it's not in use and an error otherwise.
 */
struct fscache_cookie *fscache_hash_cookie(struct fscache_cookie *candidate)
{
        struct fscache_cookie *cursor;
        struct hlist_bl_head *h;
        struct hlist_bl_node *p;
        unsigned int bucket;

        bucket = candidate->key_hash & (ARRAY_SIZE(fscache_cookie_hash) - 1);
        h = &fscache_cookie_hash[bucket];

        hlist_bl_lock(h);
        hlist_bl_for_each_entry(cursor, p, h, hash_link) {
                if (fscache_compare_cookie(candidate, cursor) == 0)
                        goto collision;
        }

        __set_bit(FSCACHE_COOKIE_ACQUIRED, &candidate->flags);
        fscache_cookie_get(candidate->parent, fscache_cookie_get_acquire_parent);
        atomic_inc(&candidate->parent->n_children);
        hlist_bl_add_head(&candidate->hash_link, h);
        hlist_bl_unlock(h);
        return candidate;

collision:
        if (test_and_set_bit(FSCACHE_COOKIE_ACQUIRED, &cursor->flags)) {
                trace_fscache_cookie(cursor, fscache_cookie_collision,
                                     atomic_read(&cursor->usage));
                pr_err("Duplicate cookie detected\n");
                fscache_print_cookie(cursor, 'O');
                fscache_print_cookie(candidate, 'N');
                hlist_bl_unlock(h);
                return NULL;
        }

        fscache_cookie_get(cursor, fscache_cookie_get_reacquire);
        hlist_bl_unlock(h);
        return cursor;
}

/*
 * request a cookie to represent an object (index, datafile, xattr, etc)
 * - parent specifies the parent object
 *   - the top level index cookie for each netfs is stored in the fscache_netfs
 *     struct upon registration
 * - def points to the definition
 * - the netfs_data will be passed to the functions pointed to in *def
 * - all attached caches will be searched to see if they contain this object
 * - index objects aren't stored on disk until there's a dependent file that
 *   needs storing
 * - other objects are stored in a selected cache immediately, and all the
 *   indices forming the path to it are instantiated if necessary
 * - we never let on to the netfs about errors
 *   - we may set a negative cookie pointer, but that's okay
 */
struct fscache_cookie *__fscache_acquire_cookie(
        struct fscache_cookie *parent,
        const struct fscache_cookie_def *def,
        const void *index_key, size_t index_key_len,
        const void *aux_data, size_t aux_data_len,
        void *netfs_data,
        loff_t object_size,
        bool enable)
{
        struct fscache_cookie *candidate, *cookie;

        BUG_ON(!def);

        _enter("{%s},{%s},%p,%u",
               parent ? (char *) parent->def->name : "<no-parent>",
               def->name, netfs_data, enable);

        if (!index_key || !index_key_len || index_key_len > 255 || aux_data_len > 255)
                return NULL;
        if (!aux_data || !aux_data_len) {
                aux_data = NULL;
                aux_data_len = 0;
        }

        fscache_stat(&fscache_n_acquires);

        /* if there's no parent cookie, then we don't create one here either */
        if (!parent) {
                fscache_stat(&fscache_n_acquires_null);
                _leave(" [no parent]");
                return NULL;
        }

        /* validate the definition */
        BUG_ON(!def->name[0]);

        BUG_ON(def->type == FSCACHE_COOKIE_TYPE_INDEX &&
               parent->type != FSCACHE_COOKIE_TYPE_INDEX);

        candidate = fscache_alloc_cookie(parent, def,
                                         index_key, index_key_len,
                                         aux_data, aux_data_len,
                                         netfs_data, object_size);
        if (!candidate) {
                fscache_stat(&fscache_n_acquires_oom);
                _leave(" [ENOMEM]");
                return NULL;
        }

        cookie = fscache_hash_cookie(candidate);
        if (!cookie) {
                trace_fscache_cookie(candidate, fscache_cookie_discard, 1);
                goto out;
        }

        if (cookie == candidate)
                candidate = NULL;

        switch (cookie->type) {
        case FSCACHE_COOKIE_TYPE_INDEX:
                fscache_stat(&fscache_n_cookie_index);
                break;
        case FSCACHE_COOKIE_TYPE_DATAFILE:
                fscache_stat(&fscache_n_cookie_data);
                break;
        default:
                fscache_stat(&fscache_n_cookie_special);
                break;
        }

        trace_fscache_acquire(cookie);

        if (enable) {
                /* if the object is an index then we need do nothing more here
                 * - we create indices on disk when we need them as an index
                 * may exist in multiple caches */
                if (cookie->type != FSCACHE_COOKIE_TYPE_INDEX) {
                        if (fscache_acquire_non_index_cookie(cookie, object_size) == 0) {
                                set_bit(FSCACHE_COOKIE_ENABLED, &cookie->flags);
                        } else {
                                atomic_dec(&parent->n_children);
                                fscache_cookie_put(cookie,
                                                   fscache_cookie_put_acquire_nobufs);
                                fscache_stat(&fscache_n_acquires_nobufs);
                                _leave(" = NULL");
                                return NULL;
                        }
                } else {
                        set_bit(FSCACHE_COOKIE_ENABLED, &cookie->flags);
                }
        }

        fscache_stat(&fscache_n_acquires_ok);

out:
        fscache_free_cookie(candidate);
        return cookie;
}
EXPORT_SYMBOL(__fscache_acquire_cookie);

/*
 * Enable a cookie to permit it to accept new operations.
 */
void __fscache_enable_cookie(struct fscache_cookie *cookie,
                             const void *aux_data,
                             loff_t object_size,
                             bool (*can_enable)(void *data),
                             void *data)
{
        _enter("%p", cookie);

        trace_fscache_enable(cookie);

        wait_on_bit_lock(&cookie->flags, FSCACHE_COOKIE_ENABLEMENT_LOCK,
                         TASK_UNINTERRUPTIBLE);

        fscache_update_aux(cookie, aux_data);

        if (test_bit(FSCACHE_COOKIE_ENABLED, &cookie->flags))
                goto out_unlock;

        if (can_enable && !can_enable(data)) {
                /* The netfs decided it didn't want to enable after all */
        } else if (cookie->type != FSCACHE_COOKIE_TYPE_INDEX) {
                /* Wait for outstanding disablement to complete */
                __fscache_wait_on_invalidate(cookie);

                if (fscache_acquire_non_index_cookie(cookie, object_size) == 0)
                        set_bit(FSCACHE_COOKIE_ENABLED, &cookie->flags);
        } else {
                set_bit(FSCACHE_COOKIE_ENABLED, &cookie->flags);
        }

out_unlock:
        clear_bit_unlock(FSCACHE_COOKIE_ENABLEMENT_LOCK, &cookie->flags);
        wake_up_bit(&cookie->flags, FSCACHE_COOKIE_ENABLEMENT_LOCK);
}
EXPORT_SYMBOL(__fscache_enable_cookie);

/*
 * acquire a non-index cookie
 * - this must make sure the index chain is instantiated and instantiate the
 *   object representation too
 */
static int fscache_acquire_non_index_cookie(struct fscache_cookie *cookie,
                                            loff_t object_size)
{
        struct fscache_object *object;
        struct fscache_cache *cache;
        int ret;

        _enter("");

        set_bit(FSCACHE_COOKIE_UNAVAILABLE, &cookie->flags);

        /* now we need to see whether the backing objects for this cookie yet
         * exist, if not there'll be nothing to search */
        down_read(&fscache_addremove_sem);

        if (list_empty(&fscache_cache_list)) {
                up_read(&fscache_addremove_sem);
                _leave(" = 0 [no caches]");
                return 0;
        }

        /* select a cache in which to store the object */
        cache = fscache_select_cache_for_object(cookie->parent);
        if (!cache) {
                up_read(&fscache_addremove_sem);
                fscache_stat(&fscache_n_acquires_no_cache);
                _leave(" = -ENOMEDIUM [no cache]");
                return -ENOMEDIUM;
        }

        _debug("cache %s", cache->tag->name);

        set_bit(FSCACHE_COOKIE_LOOKING_UP, &cookie->flags);

        /* ask the cache to allocate objects for this cookie and its parent
         * chain */
        ret = fscache_alloc_object(cache, cookie);
        if (ret < 0) {
                up_read(&fscache_addremove_sem);
                _leave(" = %d", ret);
                return ret;
        }

        spin_lock(&cookie->lock);
        if (hlist_empty(&cookie->backing_objects)) {
                spin_unlock(&cookie->lock);
                goto unavailable;
        }

        object = hlist_entry(cookie->backing_objects.first,
                             struct fscache_object, cookie_link);

        fscache_set_store_limit(object, object_size);

        /* initiate the process of looking up all the objects in the chain
         * (done by fscache_initialise_object()) */
        fscache_raise_event(object, FSCACHE_OBJECT_EV_NEW_CHILD);

        spin_unlock(&cookie->lock);

        /* we may be required to wait for lookup to complete at this point */
        if (!fscache_defer_lookup) {
                _debug("non-deferred lookup %p", &cookie->flags);
                wait_on_bit(&cookie->flags, FSCACHE_COOKIE_LOOKING_UP,
                            TASK_UNINTERRUPTIBLE);
                _debug("complete");
                if (test_bit(FSCACHE_COOKIE_UNAVAILABLE, &cookie->flags))
                        goto unavailable;
        }

        up_read(&fscache_addremove_sem);
        _leave(" = 0 [deferred]");
        return 0;

unavailable:
        up_read(&fscache_addremove_sem);
        _leave(" = -ENOBUFS");
        return -ENOBUFS;
}

/*
 * recursively allocate cache object records for a cookie/cache combination
 * - caller must be holding the addremove sem
 */
static int fscache_alloc_object(struct fscache_cache *cache,
                                struct fscache_cookie *cookie)
{
        struct fscache_object *object;
        int ret;

        _enter("%p,%p{%s}", cache, cookie, cookie->def->name);

        spin_lock(&cookie->lock);
        hlist_for_each_entry(object, &cookie->backing_objects,
                             cookie_link) {
                if (object->cache == cache)
                        goto object_already_extant;
        }
        spin_unlock(&cookie->lock);

        /* ask the cache to allocate an object (we may end up with duplicate
         * objects at this stage, but we sort that out later) */
        fscache_stat(&fscache_n_cop_alloc_object);
        object = cache->ops->alloc_object(cache, cookie);
        fscache_stat_d(&fscache_n_cop_alloc_object);
        if (IS_ERR(object)) {
                fscache_stat(&fscache_n_object_no_alloc);
                ret = PTR_ERR(object);
                goto error;
        }

        ASSERTCMP(object->cookie, ==, cookie);
        fscache_stat(&fscache_n_object_alloc);

        object->debug_id = atomic_inc_return(&fscache_object_debug_id);

        _debug("ALLOC OBJ%x: %s {%lx}",
               object->debug_id, cookie->def->name, object->events);

        ret = fscache_alloc_object(cache, cookie->parent);
        if (ret < 0)
                goto error_put;

        /* only attach if we managed to allocate all we needed, otherwise
         * discard the object we just allocated and instead use the one
         * attached to the cookie */
        if (fscache_attach_object(cookie, object) < 0) {
                fscache_stat(&fscache_n_cop_put_object);
                cache->ops->put_object(object, fscache_obj_put_attach_fail);
                fscache_stat_d(&fscache_n_cop_put_object);
        }

        _leave(" = 0");
        return 0;

object_already_extant:
        ret = -ENOBUFS;
        if (fscache_object_is_dying(object) ||
            fscache_cache_is_broken(object)) {
                spin_unlock(&cookie->lock);
                goto error;
        }
        spin_unlock(&cookie->lock);
        _leave(" = 0 [found]");
        return 0;

error_put:
        fscache_stat(&fscache_n_cop_put_object);
        cache->ops->put_object(object, fscache_obj_put_alloc_fail);
        fscache_stat_d(&fscache_n_cop_put_object);
error:
        _leave(" = %d", ret);
        return ret;
}

/*
 * attach a cache object to a cookie
 */
static int fscache_attach_object(struct fscache_cookie *cookie,
                                 struct fscache_object *object)
{
        struct fscache_object *p;
        struct fscache_cache *cache = object->cache;
        int ret;

        _enter("{%s},{OBJ%x}", cookie->def->name, object->debug_id);

        ASSERTCMP(object->cookie, ==, cookie);

        spin_lock(&cookie->lock);

        /* there may be multiple initial creations of this object, but we only
         * want one */
        ret = -EEXIST;
        hlist_for_each_entry(p, &cookie->backing_objects, cookie_link) {
                if (p->cache == object->cache) {
                        if (fscache_object_is_dying(p))
                                ret = -ENOBUFS;
                        goto cant_attach_object;
                }
        }

        /* pin the parent object */
        spin_lock_nested(&cookie->parent->lock, 1);
        hlist_for_each_entry(p, &cookie->parent->backing_objects,
                             cookie_link) {
                if (p->cache == object->cache) {
                        if (fscache_object_is_dying(p)) {
                                ret = -ENOBUFS;
                                spin_unlock(&cookie->parent->lock);
                                goto cant_attach_object;
                        }
                        object->parent = p;
                        spin_lock(&p->lock);
                        p->n_children++;
                        spin_unlock(&p->lock);
                        break;
                }
        }
        spin_unlock(&cookie->parent->lock);

        /* attach to the cache's object list */
        if (list_empty(&object->cache_link)) {
                spin_lock(&cache->object_list_lock);
                list_add(&object->cache_link, &cache->object_list);
                spin_unlock(&cache->object_list_lock);
        }

        /* Attach to the cookie.  The object already has a ref on it. */
        hlist_add_head(&object->cookie_link, &cookie->backing_objects);

        fscache_objlist_add(object);
        ret = 0;

cant_attach_object:
        spin_unlock(&cookie->lock);
        _leave(" = %d", ret);
        return ret;
}

/*
 * Invalidate an object.  Callable with spinlocks held.
 */
void __fscache_invalidate(struct fscache_cookie *cookie)
{
        struct fscache_object *object;

        _enter("{%s}", cookie->def->name);

        fscache_stat(&fscache_n_invalidates);

        /* Only permit invalidation of data files.  Invalidating an index will
         * require the caller to release all its attachments to the tree rooted
         * there, and if it's doing that, it may as well just retire the
         * cookie.
         */
        ASSERTCMP(cookie->type, ==, FSCACHE_COOKIE_TYPE_DATAFILE);

        /* If there's an object, we tell the object state machine to handle the
         * invalidation on our behalf, otherwise there's nothing to do.
         */
        if (!hlist_empty(&cookie->backing_objects)) {
                spin_lock(&cookie->lock);

                if (fscache_cookie_enabled(cookie) &&
                    !hlist_empty(&cookie->backing_objects) &&
                    !test_and_set_bit(FSCACHE_COOKIE_INVALIDATING,
                                      &cookie->flags)) {
                        object = hlist_entry(cookie->backing_objects.first,
                                             struct fscache_object,
                                             cookie_link);
                        if (fscache_object_is_live(object))
                                fscache_raise_event(
                                        object, FSCACHE_OBJECT_EV_INVALIDATE);
                }

                spin_unlock(&cookie->lock);
        }

        _leave("");
}
EXPORT_SYMBOL(__fscache_invalidate);

/*
 * Wait for object invalidation to complete.
 */
void __fscache_wait_on_invalidate(struct fscache_cookie *cookie)
{
        _enter("%p", cookie);

        wait_on_bit(&cookie->flags, FSCACHE_COOKIE_INVALIDATING,
                    TASK_UNINTERRUPTIBLE);

        _leave("");
}
EXPORT_SYMBOL(__fscache_wait_on_invalidate);

/*
 * update the index entries backing a cookie
 */
void __fscache_update_cookie(struct fscache_cookie *cookie, const void *aux_data)
{
        struct fscache_object *object;

        fscache_stat(&fscache_n_updates);

        if (!cookie) {
                fscache_stat(&fscache_n_updates_null);
                _leave(" [no cookie]");
                return;
        }

        _enter("{%s}", cookie->def->name);

        spin_lock(&cookie->lock);

        fscache_update_aux(cookie, aux_data);

        if (fscache_cookie_enabled(cookie)) {
                /* update the index entry on disk in each cache backing this
                 * cookie.
                 */
                hlist_for_each_entry(object,
                                     &cookie->backing_objects, cookie_link) {
                        fscache_raise_event(object, FSCACHE_OBJECT_EV_UPDATE);
                }
        }

        spin_unlock(&cookie->lock);
        _leave("");
}
EXPORT_SYMBOL(__fscache_update_cookie);

/*
 * Disable a cookie to stop it from accepting new requests from the netfs.
 */
void __fscache_disable_cookie(struct fscache_cookie *cookie,
                              const void *aux_data,
                              bool invalidate)
{
        struct fscache_object *object;
        bool awaken = false;

        _enter("%p,%u", cookie, invalidate);

        trace_fscache_disable(cookie);

        ASSERTCMP(atomic_read(&cookie->n_active), >, 0);

        if (atomic_read(&cookie->n_children) != 0) {
                pr_err("Cookie '%s' still has children\n",
                       cookie->def->name);
                BUG();
        }

        wait_on_bit_lock(&cookie->flags, FSCACHE_COOKIE_ENABLEMENT_LOCK,
                         TASK_UNINTERRUPTIBLE);

        fscache_update_aux(cookie, aux_data);

        if (!test_and_clear_bit(FSCACHE_COOKIE_ENABLED, &cookie->flags))
                goto out_unlock_enable;

        /* If the cookie is being invalidated, wait for that to complete first
         * so that we can reuse the flag.
         */
        __fscache_wait_on_invalidate(cookie);

        /* Dispose of the backing objects */
        set_bit(FSCACHE_COOKIE_INVALIDATING, &cookie->flags);

        spin_lock(&cookie->lock);
        if (!hlist_empty(&cookie->backing_objects)) {
                hlist_for_each_entry(object, &cookie->backing_objects, cookie_link) {
                        if (invalidate)
                                set_bit(FSCACHE_OBJECT_RETIRED, &object->flags);
                        clear_bit(FSCACHE_OBJECT_PENDING_WRITE, &object->flags);
                        fscache_raise_event(object, FSCACHE_OBJECT_EV_KILL);
                }
        } else {
                if (test_and_clear_bit(FSCACHE_COOKIE_INVALIDATING, &cookie->flags))
                        awaken = true;
        }
        spin_unlock(&cookie->lock);
        if (awaken)
                wake_up_bit(&cookie->flags, FSCACHE_COOKIE_INVALIDATING);

        /* Wait for cessation of activity requiring access to the netfs (when
         * n_active reaches 0).  This makes sure outstanding reads and writes
         * have completed.
         */
        if (!atomic_dec_and_test(&cookie->n_active)) {
                wait_var_event(&cookie->n_active,
                               !atomic_read(&cookie->n_active));
        }

        /* Make sure any pending writes are cancelled. */
        if (cookie->type != FSCACHE_COOKIE_TYPE_INDEX)
                fscache_invalidate_writes(cookie);

        /* Reset the cookie state if it wasn't relinquished */
        if (!test_bit(FSCACHE_COOKIE_RELINQUISHED, &cookie->flags)) {
                atomic_inc(&cookie->n_active);
                set_bit(FSCACHE_COOKIE_NO_DATA_YET, &cookie->flags);
        }

out_unlock_enable:
        clear_bit_unlock(FSCACHE_COOKIE_ENABLEMENT_LOCK, &cookie->flags);
        wake_up_bit(&cookie->flags, FSCACHE_COOKIE_ENABLEMENT_LOCK);
        _leave("");
}
EXPORT_SYMBOL(__fscache_disable_cookie);

/*
 * release a cookie back to the cache
 * - the object will be marked as recyclable on disk if retire is true
 * - all dependents of this cookie must have already been unregistered
 *   (indices/files/pages)
 */
void __fscache_relinquish_cookie(struct fscache_cookie *cookie,
                                 const void *aux_data,
                                 bool retire)
{
        fscache_stat(&fscache_n_relinquishes);
        if (retire)
                fscache_stat(&fscache_n_relinquishes_retire);

        if (!cookie) {
                fscache_stat(&fscache_n_relinquishes_null);
                _leave(" [no cookie]");
                return;
        }

        _enter("%p{%s,%p,%d},%d",
               cookie, cookie->def->name, cookie->netfs_data,
               atomic_read(&cookie->n_active), retire);

        trace_fscache_relinquish(cookie, retire);

        /* No further netfs-accessing operations on this cookie permitted */
        if (test_and_set_bit(FSCACHE_COOKIE_RELINQUISHED, &cookie->flags))
                BUG();

        __fscache_disable_cookie(cookie, aux_data, retire);

        /* Clear pointers back to the netfs */
        cookie->netfs_data      = NULL;
        cookie->def             = NULL;
        BUG_ON(!radix_tree_empty(&cookie->stores));

        if (cookie->parent) {
                ASSERTCMP(atomic_read(&cookie->parent->usage), >, 0);
                ASSERTCMP(atomic_read(&cookie->parent->n_children), >, 0);
                atomic_dec(&cookie->parent->n_children);
        }

        /* Dispose of the netfs's link to the cookie */
        ASSERTCMP(atomic_read(&cookie->usage), >, 0);
        fscache_cookie_put(cookie, fscache_cookie_put_relinquish);

        _leave("");
}
EXPORT_SYMBOL(__fscache_relinquish_cookie);

/*
 * Remove a cookie from the hash table.
 */
static void fscache_unhash_cookie(struct fscache_cookie *cookie)
{
        struct hlist_bl_head *h;
        unsigned int bucket;

        bucket = cookie->key_hash & (ARRAY_SIZE(fscache_cookie_hash) - 1);
        h = &fscache_cookie_hash[bucket];

        hlist_bl_lock(h);
        hlist_bl_del(&cookie->hash_link);
        hlist_bl_unlock(h);
}

/*
 * Drop a reference to a cookie.
 */
void fscache_cookie_put(struct fscache_cookie *cookie,
                        enum fscache_cookie_trace where)
{
        struct fscache_cookie *parent;
        int usage;

        _enter("%p", cookie);

        do {
                usage = atomic_dec_return(&cookie->usage);
                trace_fscache_cookie(cookie, where, usage);

                if (usage > 0)
                        return;
                BUG_ON(usage < 0);

                parent = cookie->parent;
                fscache_unhash_cookie(cookie);
                fscache_free_cookie(cookie);

                cookie = parent;
                where = fscache_cookie_put_parent;
        } while (cookie);

        _leave("");
}

/*
 * check the consistency between the netfs inode and the backing cache
 *
 * NOTE: it only serves no-index type
 */
int __fscache_check_consistency(struct fscache_cookie *cookie,
                                const void *aux_data)
{
        struct fscache_operation *op;
        struct fscache_object *object;
        bool wake_cookie = false;
        int ret;

        _enter("%p,", cookie);

        ASSERTCMP(cookie->type, ==, FSCACHE_COOKIE_TYPE_DATAFILE);

        if (fscache_wait_for_deferred_lookup(cookie) < 0)
                return -ERESTARTSYS;

        if (hlist_empty(&cookie->backing_objects))
                return 0;

        op = kzalloc(sizeof(*op), GFP_NOIO | __GFP_NOMEMALLOC | __GFP_NORETRY);
        if (!op)
                return -ENOMEM;

        fscache_operation_init(cookie, op, NULL, NULL, NULL);
        op->flags = FSCACHE_OP_MYTHREAD |
                (1 << FSCACHE_OP_WAITING) |
                (1 << FSCACHE_OP_UNUSE_COOKIE);
        trace_fscache_page_op(cookie, NULL, op, fscache_page_op_check_consistency);

        spin_lock(&cookie->lock);

        fscache_update_aux(cookie, aux_data);

        if (!fscache_cookie_enabled(cookie) ||
            hlist_empty(&cookie->backing_objects))
                goto inconsistent;
        object = hlist_entry(cookie->backing_objects.first,
                             struct fscache_object, cookie_link);
        if (test_bit(FSCACHE_IOERROR, &object->cache->flags))
                goto inconsistent;

        op->debug_id = atomic_inc_return(&fscache_op_debug_id);

        __fscache_use_cookie(cookie);
        if (fscache_submit_op(object, op) < 0)
                goto submit_failed;

        /* the work queue now carries its own ref on the object */
        spin_unlock(&cookie->lock);

        ret = fscache_wait_for_operation_activation(object, op, NULL, NULL);
        if (ret == 0) {
                /* ask the cache to honour the operation */
                ret = object->cache->ops->check_consistency(op);
                fscache_op_complete(op, false);
        } else if (ret == -ENOBUFS) {
                ret = 0;
        }

        fscache_put_operation(op);
        _leave(" = %d", ret);
        return ret;

submit_failed:
        wake_cookie = __fscache_unuse_cookie(cookie);
inconsistent:
        spin_unlock(&cookie->lock);
        if (wake_cookie)
                __fscache_wake_unused_cookie(cookie);
        kfree(op);
        _leave(" = -ESTALE");
        return -ESTALE;
}
EXPORT_SYMBOL(__fscache_check_consistency);