// SPDX-License-Identifier: GPL-2.0-or-later
/* netfs cookie management
 *
 * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * See Documentation/filesystems/caching/netfs-api.rst 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 void fscache_cookie_lru_timed_out(struct timer_list *timer);
static void fscache_cookie_lru_worker(struct work_struct *work);
static void fscache_cookie_worker(struct work_struct *work);
static void fscache_unhash_cookie(struct fscache_cookie *cookie);
static void fscache_perform_invalidation(struct fscache_cookie *cookie);

#define fscache_cookie_hash_shift 15
static struct hlist_bl_head fscache_cookie_hash[1 << fscache_cookie_hash_shift];
static LIST_HEAD(fscache_cookies);
static DEFINE_RWLOCK(fscache_cookies_lock);
static LIST_HEAD(fscache_cookie_lru);
static DEFINE_SPINLOCK(fscache_cookie_lru_lock);
DEFINE_TIMER(fscache_cookie_lru_timer, fscache_cookie_lru_timed_out);
static DECLARE_WORK(fscache_cookie_lru_work, fscache_cookie_lru_worker);
static const char fscache_cookie_states[FSCACHE_COOKIE_STATE__NR] __nonstring = "-LCAIFUWRD";
static unsigned int fscache_lru_cookie_timeout = 10 * HZ;

void fscache_print_cookie(struct fscache_cookie *cookie, char prefix)
{
        const u8 *k;

        pr_err("%c-cookie c=%08x [fl=%lx na=%u nA=%u s=%c]\n",
               prefix,
               cookie->debug_id,
               cookie->flags,
               atomic_read(&cookie->n_active),
               atomic_read(&cookie->n_accesses),
               fscache_cookie_states[cookie->state]);
        pr_err("%c-cookie V=%08x [%s]\n",
               prefix,
               cookie->volume->debug_id,
               cookie->volume->key);

        k = (cookie->key_len <= sizeof(cookie->inline_key)) ?
                cookie->inline_key : cookie->key;
        pr_err("%c-key=[%u] '%*phN'\n", prefix, cookie->key_len, cookie->key_len, k);
}

static void fscache_free_cookie(struct fscache_cookie *cookie)
{
        if (WARN_ON_ONCE(!list_empty(&cookie->commit_link))) {
                spin_lock(&fscache_cookie_lru_lock);
                list_del_init(&cookie->commit_link);
                spin_unlock(&fscache_cookie_lru_lock);
                fscache_stat_d(&fscache_n_cookies_lru);
                fscache_stat(&fscache_n_cookies_lru_removed);
        }

        if (WARN_ON_ONCE(test_bit(FSCACHE_COOKIE_IS_HASHED, &cookie->flags))) {
                fscache_print_cookie(cookie, 'F');
                return;
        }

        write_lock(&fscache_cookies_lock);
        list_del(&cookie->proc_link);
        write_unlock(&fscache_cookies_lock);
        if (cookie->aux_len > sizeof(cookie->inline_aux))
                kfree(cookie->aux);
        if (cookie->key_len > sizeof(cookie->inline_key))
                kfree(cookie->key);
        fscache_stat_d(&fscache_n_cookies);
        kmem_cache_free(fscache_cookie_jar, cookie);
}

static void __fscache_queue_cookie(struct fscache_cookie *cookie)
{
        if (!queue_work(fscache_wq, &cookie->work))
                fscache_put_cookie(cookie, fscache_cookie_put_over_queued);
}

static void fscache_queue_cookie(struct fscache_cookie *cookie,
                                 enum fscache_cookie_trace where)
{
        fscache_get_cookie(cookie, where);
        __fscache_queue_cookie(cookie);
}

/*
 * Initialise the access gate on a cookie by setting a flag to prevent the
 * state machine from being queued when the access counter transitions to 0.
 * We're only interested in this when we withdraw caching services from the
 * cookie.
 */
static void fscache_init_access_gate(struct fscache_cookie *cookie)
{
        int n_accesses;

        n_accesses = atomic_read(&cookie->n_accesses);
        trace_fscache_access(cookie->debug_id, refcount_read(&cookie->ref),
                             n_accesses, fscache_access_cache_pin);
        set_bit(FSCACHE_COOKIE_NO_ACCESS_WAKE, &cookie->flags);
}

/**
 * fscache_end_cookie_access - Unpin a cache at the end of an access.
 * @cookie: A data file cookie
 * @why: An indication of the circumstances of the access for tracing
 *
 * Unpin a cache cookie after we've accessed it and bring a deferred
 * relinquishment or withdrawal state into effect.
 *
 * The @why indicator is provided for tracing purposes.
 */
void fscache_end_cookie_access(struct fscache_cookie *cookie,
                               enum fscache_access_trace why)
{
        int n_accesses;

        smp_mb__before_atomic();
        n_accesses = atomic_dec_return(&cookie->n_accesses);
        trace_fscache_access(cookie->debug_id, refcount_read(&cookie->ref),
                             n_accesses, why);
        if (n_accesses == 0 &&
            !test_bit(FSCACHE_COOKIE_NO_ACCESS_WAKE, &cookie->flags))
                fscache_queue_cookie(cookie, fscache_cookie_get_end_access);
}
EXPORT_SYMBOL(fscache_end_cookie_access);

/*
 * Pin the cache behind a cookie so that we can access it.
 */
static void __fscache_begin_cookie_access(struct fscache_cookie *cookie,
                                          enum fscache_access_trace why)
{
        int n_accesses;

        n_accesses = atomic_inc_return(&cookie->n_accesses);
        smp_mb__after_atomic(); /* (Future) read state after is-caching.
                                 * Reread n_accesses after is-caching
                                 */
        trace_fscache_access(cookie->debug_id, refcount_read(&cookie->ref),
                             n_accesses, why);
}

/**
 * fscache_begin_cookie_access - Pin a cache so data can be accessed
 * @cookie: A data file cookie
 * @why: An indication of the circumstances of the access for tracing
 *
 * Attempt to pin the cache to prevent it from going away whilst we're
 * accessing data and returns true if successful.  This works as follows:
 *
 *  (1) If the cookie is not being cached (ie. FSCACHE_COOKIE_IS_CACHING is not
 *      set), we return false to indicate access was not permitted.
 *
 *  (2) If the cookie is being cached, we increment its n_accesses count and
 *      then recheck the IS_CACHING flag, ending the access if it got cleared.
 *
 *  (3) When we end the access, we decrement the cookie's n_accesses and wake
 *      up the any waiters if it reaches 0.
 *
 *  (4) Whilst the cookie is actively being cached, its n_accesses is kept
 *      artificially incremented to prevent wakeups from happening.
 *
 *  (5) When the cache is taken offline or if the cookie is culled, the flag is
 *      cleared to prevent new accesses, the cookie's n_accesses is decremented
 *      and we wait for it to become 0.
 *
 * The @why indicator are merely provided for tracing purposes.
 */
bool fscache_begin_cookie_access(struct fscache_cookie *cookie,
                                 enum fscache_access_trace why)
{
        if (!test_bit(FSCACHE_COOKIE_IS_CACHING, &cookie->flags))
                return false;
        __fscache_begin_cookie_access(cookie, why);
        if (!test_bit(FSCACHE_COOKIE_IS_CACHING, &cookie->flags) ||
            !fscache_cache_is_live(cookie->volume->cache)) {
                fscache_end_cookie_access(cookie, fscache_access_unlive);
                return false;
        }
        return true;
}

static inline void wake_up_cookie_state(struct fscache_cookie *cookie)
{
        /* Use a barrier to ensure that waiters see the state variable
         * change, as spin_unlock doesn't guarantee a barrier.
         *
         * See comments over wake_up_bit() and waitqueue_active().
         */
        smp_mb();
        wake_up_var(&cookie->state);
}

/*
 * Change the state a cookie is at and wake up anyone waiting for that.  Impose
 * an ordering between the stuff stored in the cookie and the state member.
 * Paired with fscache_cookie_state().
 */
static void __fscache_set_cookie_state(struct fscache_cookie *cookie,
                                       enum fscache_cookie_state state)
{
        smp_store_release(&cookie->state, state);
}

static void fscache_set_cookie_state(struct fscache_cookie *cookie,
                                     enum fscache_cookie_state state)
{
        spin_lock(&cookie->lock);
        __fscache_set_cookie_state(cookie, state);
        spin_unlock(&cookie->lock);
        wake_up_cookie_state(cookie);
}

/**
 * fscache_cookie_lookup_negative - Note negative lookup
 * @cookie: The cookie that was being looked up
 *
 * Note that some part of the metadata path in the cache doesn't exist and so
 * we can release any waiting readers in the certain knowledge that there's
 * nothing for them to actually read.
 *
 * This function uses no locking and must only be called from the state machine.
 */
void fscache_cookie_lookup_negative(struct fscache_cookie *cookie)
{
        set_bit(FSCACHE_COOKIE_NO_DATA_TO_READ, &cookie->flags);
        fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_CREATING);
}
EXPORT_SYMBOL(fscache_cookie_lookup_negative);

/**
 * fscache_resume_after_invalidation - Allow I/O to resume after invalidation
 * @cookie: The cookie that was invalidated
 *
 * Tell fscache that invalidation is sufficiently complete that I/O can be
 * allowed again.
 */
void fscache_resume_after_invalidation(struct fscache_cookie *cookie)
{
        fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_ACTIVE);
}
EXPORT_SYMBOL(fscache_resume_after_invalidation);

/**
 * fscache_caching_failed - Report that a failure stopped caching on a cookie
 * @cookie: The cookie that was affected
 *
 * Tell fscache that caching on a cookie needs to be stopped due to some sort
 * of failure.
 *
 * This function uses no locking and must only be called from the state machine.
 */
void fscache_caching_failed(struct fscache_cookie *cookie)
{
        clear_bit(FSCACHE_COOKIE_IS_CACHING, &cookie->flags);
        fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_FAILED);
        trace_fscache_cookie(cookie->debug_id, refcount_read(&cookie->ref),
                                fscache_cookie_failed);
}
EXPORT_SYMBOL(fscache_caching_failed);

/*
 * 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)
{
        void *buf;
        size_t buf_size;

        buf_size = round_up(index_key_len, sizeof(__le32));

        if (index_key_len > sizeof(cookie->inline_key)) {
                buf = kzalloc(buf_size, GFP_KERNEL);
                if (!buf)
                        return -ENOMEM;
                cookie->key = buf;
        } else {
                buf = cookie->inline_key;
        }

        memcpy(buf, index_key, index_key_len);
        cookie->key_hash = fscache_hash(cookie->volume->key_hash,
                                        buf, buf_size);
        return 0;
}

static bool fscache_cookie_same(const struct fscache_cookie *a,
                                const struct fscache_cookie *b)
{
        const void *ka, *kb;

        if (a->key_hash != b->key_hash ||
            a->volume   != b->volume ||
            a->key_len  != b->key_len)
                return false;

        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) == 0;
}

static atomic_t fscache_cookie_debug_id = ATOMIC_INIT(1);

/*
 * Allocate a cookie.
 */
static struct fscache_cookie *fscache_alloc_cookie(
        struct fscache_volume *volume,
        u8 advice,
        const void *index_key, size_t index_key_len,
        const void *aux_data, size_t aux_data_len,
        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;
        fscache_stat(&fscache_n_cookies);

        cookie->volume          = volume;
        cookie->advice          = advice;
        cookie->key_len         = index_key_len;
        cookie->aux_len         = aux_data_len;
        cookie->object_size     = object_size;
        if (object_size == 0)
                __set_bit(FSCACHE_COOKIE_NO_DATA_TO_READ, &cookie->flags);

        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;
        }

        refcount_set(&cookie->ref, 1);
        cookie->debug_id = atomic_inc_return(&fscache_cookie_debug_id);
        spin_lock_init(&cookie->lock);
        INIT_LIST_HEAD(&cookie->commit_link);
        INIT_WORK(&cookie->work, fscache_cookie_worker);
        __fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_QUIESCENT);

        write_lock(&fscache_cookies_lock);
        list_add_tail(&cookie->proc_link, &fscache_cookies);
        write_unlock(&fscache_cookies_lock);
        fscache_see_cookie(cookie, fscache_cookie_new_acquire);
        return cookie;

nomem:
        fscache_free_cookie(cookie);
        return NULL;
}

static inline bool fscache_cookie_is_dropped(struct fscache_cookie *cookie)
{
        return READ_ONCE(cookie->state) == FSCACHE_COOKIE_STATE_DROPPED;
}

static void fscache_wait_on_collision(struct fscache_cookie *candidate,
                                      struct fscache_cookie *wait_for)
{
        enum fscache_cookie_state *statep = &wait_for->state;

        wait_var_event_timeout(statep, fscache_cookie_is_dropped(wait_for),
                               20 * HZ);
        if (!fscache_cookie_is_dropped(wait_for)) {
                pr_notice("Potential collision c=%08x old: c=%08x",
                          candidate->debug_id, wait_for->debug_id);
                wait_var_event(statep, fscache_cookie_is_dropped(wait_for));
        }
}

/*
 * Attempt to insert the new cookie into the hash.  If there's a collision, we
 * wait for the old cookie to complete if it's being relinquished and an error
 * otherwise.
 */
static bool fscache_hash_cookie(struct fscache_cookie *candidate)
{
        struct fscache_cookie *cursor, *wait_for = NULL;
        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_cookie_same(candidate, cursor)) {
                        if (!test_bit(FSCACHE_COOKIE_RELINQUISHED, &cursor->flags))
                                goto collision;
                        wait_for = fscache_get_cookie(cursor,
                                                      fscache_cookie_get_hash_collision);
                        break;
                }
        }

        fscache_get_volume(candidate->volume, fscache_volume_get_cookie);
        atomic_inc(&candidate->volume->n_cookies);
        hlist_bl_add_head(&candidate->hash_link, h);
        set_bit(FSCACHE_COOKIE_IS_HASHED, &candidate->flags);
        hlist_bl_unlock(h);

        if (wait_for) {
                fscache_wait_on_collision(candidate, wait_for);
                fscache_put_cookie(wait_for, fscache_cookie_put_hash_collision);
        }
        return true;

collision:
        trace_fscache_cookie(cursor->debug_id, refcount_read(&cursor->ref),
                             fscache_cookie_collision);
        pr_err("Duplicate cookie detected\n");
        fscache_print_cookie(cursor, 'O');
        fscache_print_cookie(candidate, 'N');
        hlist_bl_unlock(h);
        return false;
}

/*
 * Request a cookie to represent a data storage object within a volume.
 *
 * 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_volume *volume,
        u8 advice,
        const void *index_key, size_t index_key_len,
        const void *aux_data, size_t aux_data_len,
        loff_t object_size)
{
        struct fscache_cookie *cookie;

        _enter("V=%x", volume->debug_id);

        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);

        cookie = fscache_alloc_cookie(volume, advice,
                                      index_key, index_key_len,
                                      aux_data, aux_data_len,
                                      object_size);
        if (!cookie) {
                fscache_stat(&fscache_n_acquires_oom);
                return NULL;
        }

        if (!fscache_hash_cookie(cookie)) {
                fscache_see_cookie(cookie, fscache_cookie_discard);
                fscache_free_cookie(cookie);
                return NULL;
        }

        trace_fscache_acquire(cookie);
        fscache_stat(&fscache_n_acquires_ok);
        _leave(" = c=%08x", cookie->debug_id);
        return cookie;
}
EXPORT_SYMBOL(__fscache_acquire_cookie);

/*
 * Prepare a cache object to be written to.
 */
static void fscache_prepare_to_write(struct fscache_cookie *cookie)
{
        cookie->volume->cache->ops->prepare_to_write(cookie);
}

/*
 * Look up a cookie in the cache.
 */
static void fscache_perform_lookup(struct fscache_cookie *cookie)
{
        enum fscache_access_trace trace = fscache_access_lookup_cookie_end_failed;
        bool need_withdraw = false;

        _enter("");

        if (!cookie->volume->cache_priv) {
                fscache_create_volume(cookie->volume, true);
                if (!cookie->volume->cache_priv) {
                        fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_QUIESCENT);
                        goto out;
                }
        }

        if (!cookie->volume->cache->ops->lookup_cookie(cookie)) {
                if (cookie->state != FSCACHE_COOKIE_STATE_FAILED)
                        fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_QUIESCENT);
                need_withdraw = true;
                _leave(" [fail]");
                goto out;
        }

        fscache_see_cookie(cookie, fscache_cookie_see_active);
        spin_lock(&cookie->lock);
        if (test_and_clear_bit(FSCACHE_COOKIE_DO_INVALIDATE, &cookie->flags))
                __fscache_set_cookie_state(cookie,
                                           FSCACHE_COOKIE_STATE_INVALIDATING);
        else
                __fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_ACTIVE);
        spin_unlock(&cookie->lock);
        wake_up_cookie_state(cookie);
        trace = fscache_access_lookup_cookie_end;

out:
        fscache_end_cookie_access(cookie, trace);
        if (need_withdraw)
                fscache_withdraw_cookie(cookie);
        fscache_end_volume_access(cookie->volume, cookie, trace);
}

/*
 * Begin the process of looking up a cookie.  We offload the actual process to
 * a worker thread.
 */
static bool fscache_begin_lookup(struct fscache_cookie *cookie, bool will_modify)
{
        if (will_modify) {
                set_bit(FSCACHE_COOKIE_LOCAL_WRITE, &cookie->flags);
                set_bit(FSCACHE_COOKIE_DO_PREP_TO_WRITE, &cookie->flags);
        }
        if (!fscache_begin_volume_access(cookie->volume, cookie,
                                         fscache_access_lookup_cookie))
                return false;

        __fscache_begin_cookie_access(cookie, fscache_access_lookup_cookie);
        __fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_LOOKING_UP);
        set_bit(FSCACHE_COOKIE_IS_CACHING, &cookie->flags);
        set_bit(FSCACHE_COOKIE_HAS_BEEN_CACHED, &cookie->flags);
        return true;
}

/*
 * Start using the cookie for I/O.  This prevents the backing object from being
 * reaped by VM pressure.
 */
void __fscache_use_cookie(struct fscache_cookie *cookie, bool will_modify)
{
        enum fscache_cookie_state state;
        bool queue = false;
        int n_active;

        _enter("c=%08x", cookie->debug_id);

        if (WARN(test_bit(FSCACHE_COOKIE_RELINQUISHED, &cookie->flags),
                 "Trying to use relinquished cookie\n"))
                return;

        spin_lock(&cookie->lock);

        n_active = atomic_inc_return(&cookie->n_active);
        trace_fscache_active(cookie->debug_id, refcount_read(&cookie->ref),
                             n_active, atomic_read(&cookie->n_accesses),
                             will_modify ?
                             fscache_active_use_modify : fscache_active_use);

again:
        state = fscache_cookie_state(cookie);
        switch (state) {
        case FSCACHE_COOKIE_STATE_QUIESCENT:
                queue = fscache_begin_lookup(cookie, will_modify);
                break;

        case FSCACHE_COOKIE_STATE_LOOKING_UP:
        case FSCACHE_COOKIE_STATE_CREATING:
                if (will_modify)
                        set_bit(FSCACHE_COOKIE_LOCAL_WRITE, &cookie->flags);
                break;
        case FSCACHE_COOKIE_STATE_ACTIVE:
        case FSCACHE_COOKIE_STATE_INVALIDATING:
                if (will_modify &&
                    !test_and_set_bit(FSCACHE_COOKIE_LOCAL_WRITE, &cookie->flags)) {
                        set_bit(FSCACHE_COOKIE_DO_PREP_TO_WRITE, &cookie->flags);
                        queue = true;
                }
                /*
                 * We could race with cookie_lru which may set LRU_DISCARD bit
                 * but has yet to run the cookie state machine.  If this happens
                 * and another thread tries to use the cookie, clear LRU_DISCARD
                 * so we don't end up withdrawing the cookie while in use.
                 */
                if (test_and_clear_bit(FSCACHE_COOKIE_DO_LRU_DISCARD, &cookie->flags))
                        fscache_see_cookie(cookie, fscache_cookie_see_lru_discard_clear);
                break;

        case FSCACHE_COOKIE_STATE_FAILED:
        case FSCACHE_COOKIE_STATE_WITHDRAWING:
                break;

        case FSCACHE_COOKIE_STATE_LRU_DISCARDING:
                spin_unlock(&cookie->lock);
                wait_var_event(&cookie->state,
                               fscache_cookie_state(cookie) !=
                               FSCACHE_COOKIE_STATE_LRU_DISCARDING);
                spin_lock(&cookie->lock);
                goto again;

        case FSCACHE_COOKIE_STATE_DROPPED:
        case FSCACHE_COOKIE_STATE_RELINQUISHING:
                WARN(1, "Can't use cookie in state %u\n", state);
                break;
        }

        spin_unlock(&cookie->lock);
        if (queue)
                fscache_queue_cookie(cookie, fscache_cookie_get_use_work);
        _leave("");
}
EXPORT_SYMBOL(__fscache_use_cookie);

static void fscache_unuse_cookie_locked(struct fscache_cookie *cookie)
{
        clear_bit(FSCACHE_COOKIE_DISABLED, &cookie->flags);
        if (!test_bit(FSCACHE_COOKIE_IS_CACHING, &cookie->flags))
                return;

        cookie->unused_at = jiffies;
        spin_lock(&fscache_cookie_lru_lock);
        if (list_empty(&cookie->commit_link)) {
                fscache_get_cookie(cookie, fscache_cookie_get_lru);
                fscache_stat(&fscache_n_cookies_lru);
        }
        list_move_tail(&cookie->commit_link, &fscache_cookie_lru);

        spin_unlock(&fscache_cookie_lru_lock);
        timer_reduce(&fscache_cookie_lru_timer,
                     jiffies + fscache_lru_cookie_timeout);
}

/*
 * Stop using the cookie for I/O.
 */
void __fscache_unuse_cookie(struct fscache_cookie *cookie,
                            const void *aux_data, const loff_t *object_size)
{
        unsigned int debug_id = cookie->debug_id;
        unsigned int r = refcount_read(&cookie->ref);
        unsigned int a = atomic_read(&cookie->n_accesses);
        unsigned int c;

        if (aux_data || object_size)
                __fscache_update_cookie(cookie, aux_data, object_size);

        /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
        c = atomic_fetch_add_unless(&cookie->n_active, -1, 1);
        if (c != 1) {
                trace_fscache_active(debug_id, r, c - 1, a, fscache_active_unuse);
                return;
        }

        spin_lock(&cookie->lock);
        r = refcount_read(&cookie->ref);
        a = atomic_read(&cookie->n_accesses);
        c = atomic_dec_return(&cookie->n_active);
        trace_fscache_active(debug_id, r, c, a, fscache_active_unuse);
        if (c == 0)
                fscache_unuse_cookie_locked(cookie);
        spin_unlock(&cookie->lock);
}
EXPORT_SYMBOL(__fscache_unuse_cookie);

/*
 * Perform work upon the cookie, such as committing its cache state,
 * relinquishing it or withdrawing the backing cache.  We're protected from the
 * cache going away under us as object withdrawal must come through this
 * non-reentrant work item.
 */
static void fscache_cookie_state_machine(struct fscache_cookie *cookie)
{
        enum fscache_cookie_state state;
        bool wake = false;

        _enter("c=%x", cookie->debug_id);

again:
        spin_lock(&cookie->lock);
again_locked:
        state = cookie->state;
        switch (state) {
        case FSCACHE_COOKIE_STATE_QUIESCENT:
                /* The QUIESCENT state is jumped to the LOOKING_UP state by
                 * fscache_use_cookie().
                 */

                if (atomic_read(&cookie->n_accesses) == 0 &&
                    test_bit(FSCACHE_COOKIE_DO_RELINQUISH, &cookie->flags)) {
                        __fscache_set_cookie_state(cookie,
                                                   FSCACHE_COOKIE_STATE_RELINQUISHING);
                        wake = true;
                        goto again_locked;
                }
                break;

        case FSCACHE_COOKIE_STATE_LOOKING_UP:
                spin_unlock(&cookie->lock);
                fscache_init_access_gate(cookie);
                fscache_perform_lookup(cookie);
                goto again;

        case FSCACHE_COOKIE_STATE_INVALIDATING:
                spin_unlock(&cookie->lock);
                fscache_perform_invalidation(cookie);
                goto again;

        case FSCACHE_COOKIE_STATE_ACTIVE:
                if (test_and_clear_bit(FSCACHE_COOKIE_DO_PREP_TO_WRITE, &cookie->flags)) {
                        spin_unlock(&cookie->lock);
                        fscache_prepare_to_write(cookie);
                        spin_lock(&cookie->lock);
                }
                if (test_bit(FSCACHE_COOKIE_DO_LRU_DISCARD, &cookie->flags)) {
                        if (atomic_read(&cookie->n_accesses) != 0)
                                /* still being accessed: postpone it */
                                break;

                        __fscache_set_cookie_state(cookie,
                                                   FSCACHE_COOKIE_STATE_LRU_DISCARDING);
                        wake = true;
                        goto again_locked;
                }
                fallthrough;

        case FSCACHE_COOKIE_STATE_FAILED:
                if (test_and_clear_bit(FSCACHE_COOKIE_DO_INVALIDATE, &cookie->flags))
                        fscache_end_cookie_access(cookie, fscache_access_invalidate_cookie_end);

                if (atomic_read(&cookie->n_accesses) != 0)
                        break;
                if (test_bit(FSCACHE_COOKIE_DO_RELINQUISH, &cookie->flags)) {
                        __fscache_set_cookie_state(cookie,
                                                   FSCACHE_COOKIE_STATE_RELINQUISHING);
                        wake = true;
                        goto again_locked;
                }
                if (test_bit(FSCACHE_COOKIE_DO_WITHDRAW, &cookie->flags)) {
                        __fscache_set_cookie_state(cookie,
                                                   FSCACHE_COOKIE_STATE_WITHDRAWING);
                        wake = true;
                        goto again_locked;
                }
                break;

        case FSCACHE_COOKIE_STATE_LRU_DISCARDING:
        case FSCACHE_COOKIE_STATE_RELINQUISHING:
        case FSCACHE_COOKIE_STATE_WITHDRAWING:
                if (cookie->cache_priv) {
                        spin_unlock(&cookie->lock);
                        cookie->volume->cache->ops->withdraw_cookie(cookie);
                        spin_lock(&cookie->lock);
                }

                if (test_and_clear_bit(FSCACHE_COOKIE_DO_INVALIDATE, &cookie->flags))
                        fscache_end_cookie_access(cookie, fscache_access_invalidate_cookie_end);

                switch (state) {
                case FSCACHE_COOKIE_STATE_RELINQUISHING:
                        fscache_see_cookie(cookie, fscache_cookie_see_relinquish);
                        fscache_unhash_cookie(cookie);
                        __fscache_set_cookie_state(cookie,
                                                   FSCACHE_COOKIE_STATE_DROPPED);
                        wake = true;
                        goto out;
                case FSCACHE_COOKIE_STATE_LRU_DISCARDING:
                        fscache_see_cookie(cookie, fscache_cookie_see_lru_discard);
                        break;
                case FSCACHE_COOKIE_STATE_WITHDRAWING:
                        fscache_see_cookie(cookie, fscache_cookie_see_withdraw);
                        break;
                default:
                        BUG();
                }

                clear_bit(FSCACHE_COOKIE_NEEDS_UPDATE, &cookie->flags);
                clear_bit(FSCACHE_COOKIE_DO_WITHDRAW, &cookie->flags);
                clear_bit(FSCACHE_COOKIE_DO_LRU_DISCARD, &cookie->flags);
                clear_bit(FSCACHE_COOKIE_DO_PREP_TO_WRITE, &cookie->flags);
                set_bit(FSCACHE_COOKIE_NO_DATA_TO_READ, &cookie->flags);
                __fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_QUIESCENT);
                wake = true;
                goto again_locked;

        case FSCACHE_COOKIE_STATE_DROPPED:
                break;

        default:
                WARN_ONCE(1, "Cookie %x in unexpected state %u\n",
                          cookie->debug_id, state);
                break;
        }

out:
        spin_unlock(&cookie->lock);
        if (wake)
                wake_up_cookie_state(cookie);
        _leave("");
}

static void fscache_cookie_worker(struct work_struct *work)
{
        struct fscache_cookie *cookie = container_of(work, struct fscache_cookie, work);

        fscache_see_cookie(cookie, fscache_cookie_see_work);
        fscache_cookie_state_machine(cookie);
        fscache_put_cookie(cookie, fscache_cookie_put_work);
}

/*
 * Wait for the object to become inactive.  The cookie's work item will be
 * scheduled when someone transitions n_accesses to 0 - but if someone's
 * already done that, schedule it anyway.
 */
static void __fscache_withdraw_cookie(struct fscache_cookie *cookie)
{
        int n_accesses;
        bool unpinned;

        unpinned = test_and_clear_bit(FSCACHE_COOKIE_NO_ACCESS_WAKE, &cookie->flags);

        /* Need to read the access count after unpinning */
        n_accesses = atomic_read(&cookie->n_accesses);
        if (unpinned)
                trace_fscache_access(cookie->debug_id, refcount_read(&cookie->ref),
                                     n_accesses, fscache_access_cache_unpin);
        if (n_accesses == 0)
                fscache_queue_cookie(cookie, fscache_cookie_get_end_access);
}

static void fscache_cookie_lru_do_one(struct fscache_cookie *cookie)
{
        fscache_see_cookie(cookie, fscache_cookie_see_lru_do_one);

        spin_lock(&cookie->lock);
        if (cookie->state != FSCACHE_COOKIE_STATE_ACTIVE ||
            time_before(jiffies, cookie->unused_at + fscache_lru_cookie_timeout) ||
            atomic_read(&cookie->n_active) > 0) {
                spin_unlock(&cookie->lock);
                fscache_stat(&fscache_n_cookies_lru_removed);
        } else {
                set_bit(FSCACHE_COOKIE_DO_LRU_DISCARD, &cookie->flags);
                spin_unlock(&cookie->lock);
                fscache_stat(&fscache_n_cookies_lru_expired);
                _debug("lru c=%x", cookie->debug_id);
                __fscache_withdraw_cookie(cookie);
        }

        fscache_put_cookie(cookie, fscache_cookie_put_lru);
}

static void fscache_cookie_lru_worker(struct work_struct *work)
{
        struct fscache_cookie *cookie;
        unsigned long unused_at;

        spin_lock(&fscache_cookie_lru_lock);

        while (!list_empty(&fscache_cookie_lru)) {
                cookie = list_first_entry(&fscache_cookie_lru,
                                          struct fscache_cookie, commit_link);
                unused_at = cookie->unused_at + fscache_lru_cookie_timeout;
                if (time_before(jiffies, unused_at)) {
                        timer_reduce(&fscache_cookie_lru_timer, unused_at);
                        break;
                }

                list_del_init(&cookie->commit_link);
                fscache_stat_d(&fscache_n_cookies_lru);
                spin_unlock(&fscache_cookie_lru_lock);
                fscache_cookie_lru_do_one(cookie);
                spin_lock(&fscache_cookie_lru_lock);
        }

        spin_unlock(&fscache_cookie_lru_lock);
}

static void fscache_cookie_lru_timed_out(struct timer_list *timer)
{
        queue_work(fscache_wq, &fscache_cookie_lru_work);
}

static void fscache_cookie_drop_from_lru(struct fscache_cookie *cookie)
{
        bool need_put = false;

        if (!list_empty(&cookie->commit_link)) {
                spin_lock(&fscache_cookie_lru_lock);
                if (!list_empty(&cookie->commit_link)) {
                        list_del_init(&cookie->commit_link);
                        fscache_stat_d(&fscache_n_cookies_lru);
                        fscache_stat(&fscache_n_cookies_lru_dropped);
                        need_put = true;
                }
                spin_unlock(&fscache_cookie_lru_lock);
                if (need_put)
                        fscache_put_cookie(cookie, fscache_cookie_put_lru);
        }
}

/*
 * 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);
        clear_bit(FSCACHE_COOKIE_IS_HASHED, &cookie->flags);
        hlist_bl_unlock(h);
        fscache_stat(&fscache_n_relinquishes_dropped);
}

static void fscache_drop_withdraw_cookie(struct fscache_cookie *cookie)
{
        fscache_cookie_drop_from_lru(cookie);
        __fscache_withdraw_cookie(cookie);
}

/**
 * fscache_withdraw_cookie - Mark a cookie for withdrawal
 * @cookie: The cookie to be withdrawn.
 *
 * Allow the cache backend to withdraw the backing for a cookie for its own
 * reasons, even if that cookie is in active use.
 */
void fscache_withdraw_cookie(struct fscache_cookie *cookie)
{
        set_bit(FSCACHE_COOKIE_DO_WITHDRAW, &cookie->flags);
        fscache_drop_withdraw_cookie(cookie);
}
EXPORT_SYMBOL(fscache_withdraw_cookie);

/*
 * Allow the netfs to release a cookie back to the cache.
 * - the object will be marked as recyclable on disk if retire is true
 */
void __fscache_relinquish_cookie(struct fscache_cookie *cookie, bool retire)
{
        fscache_stat(&fscache_n_relinquishes);
        if (retire)
                fscache_stat(&fscache_n_relinquishes_retire);

        _enter("c=%08x{%d},%d",
               cookie->debug_id, atomic_read(&cookie->n_active), retire);

        if (WARN(test_and_set_bit(FSCACHE_COOKIE_RELINQUISHED, &cookie->flags),
                 "Cookie c=%x already relinquished\n", cookie->debug_id))
                return;

        if (retire)
                set_bit(FSCACHE_COOKIE_RETIRED, &cookie->flags);
        trace_fscache_relinquish(cookie, retire);

        ASSERTCMP(atomic_read(&cookie->n_active), ==, 0);
        ASSERTCMP(atomic_read(&cookie->volume->n_cookies), >, 0);
        atomic_dec(&cookie->volume->n_cookies);

        if (test_bit(FSCACHE_COOKIE_HAS_BEEN_CACHED, &cookie->flags)) {
                set_bit(FSCACHE_COOKIE_DO_RELINQUISH, &cookie->flags);
                fscache_drop_withdraw_cookie(cookie);
        } else {
                fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_DROPPED);
                fscache_unhash_cookie(cookie);
        }
        fscache_put_cookie(cookie, fscache_cookie_put_relinquish);
}
EXPORT_SYMBOL(__fscache_relinquish_cookie);

/*
 * Drop a reference to a cookie.
 */
void fscache_put_cookie(struct fscache_cookie *cookie,
                        enum fscache_cookie_trace where)
{
        struct fscache_volume *volume = cookie->volume;
        unsigned int cookie_debug_id = cookie->debug_id;
        bool zero;
        int ref;

        zero = __refcount_dec_and_test(&cookie->ref, &ref);
        trace_fscache_cookie(cookie_debug_id, ref - 1, where);
        if (zero) {
                fscache_free_cookie(cookie);
                fscache_put_volume(volume, fscache_volume_put_cookie);
        }
}
EXPORT_SYMBOL(fscache_put_cookie);

/*
 * Get a reference to a cookie.
 */
struct fscache_cookie *fscache_get_cookie(struct fscache_cookie *cookie,
                                          enum fscache_cookie_trace where)
{
        int ref;

        __refcount_inc(&cookie->ref, &ref);
        trace_fscache_cookie(cookie->debug_id, ref + 1, where);
        return cookie;
}
EXPORT_SYMBOL(fscache_get_cookie);

/*
 * Ask the cache to effect invalidation of a cookie.
 */
static void fscache_perform_invalidation(struct fscache_cookie *cookie)
{
        if (!cookie->volume->cache->ops->invalidate_cookie(cookie))
                fscache_caching_failed(cookie);
        fscache_end_cookie_access(cookie, fscache_access_invalidate_cookie_end);
}

/*
 * Invalidate an object.
 */
void __fscache_invalidate(struct fscache_cookie *cookie,
                          const void *aux_data, loff_t new_size,
                          unsigned int flags)
{
        bool is_caching;

        _enter("c=%x", cookie->debug_id);

        fscache_stat(&fscache_n_invalidates);

        if (WARN(test_bit(FSCACHE_COOKIE_RELINQUISHED, &cookie->flags),
                 "Trying to invalidate relinquished cookie\n"))
                return;

        if ((flags & FSCACHE_INVAL_DIO_WRITE) &&
            test_and_set_bit(FSCACHE_COOKIE_DISABLED, &cookie->flags))
                return;

        spin_lock(&cookie->lock);
        set_bit(FSCACHE_COOKIE_NO_DATA_TO_READ, &cookie->flags);
        fscache_update_aux(cookie, aux_data, &new_size);
        cookie->inval_counter++;
        trace_fscache_invalidate(cookie, new_size);

        switch (cookie->state) {
        case FSCACHE_COOKIE_STATE_INVALIDATING: /* is_still_valid will catch it */
        default:
                spin_unlock(&cookie->lock);
                _leave(" [no %u]", cookie->state);
                return;

        case FSCACHE_COOKIE_STATE_LOOKING_UP:
                if (!test_and_set_bit(FSCACHE_COOKIE_DO_INVALIDATE, &cookie->flags))
                        __fscache_begin_cookie_access(cookie, fscache_access_invalidate_cookie);
                fallthrough;
        case FSCACHE_COOKIE_STATE_CREATING:
                spin_unlock(&cookie->lock);
                _leave(" [look %x]", cookie->inval_counter);
                return;

        case FSCACHE_COOKIE_STATE_ACTIVE:
                is_caching = fscache_begin_cookie_access(
                        cookie, fscache_access_invalidate_cookie);
                if (is_caching)
                        __fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_INVALIDATING);
                spin_unlock(&cookie->lock);
                wake_up_cookie_state(cookie);

                if (is_caching)
                        fscache_queue_cookie(cookie, fscache_cookie_get_inval_work);
                _leave(" [inv]");
                return;
        }
}
EXPORT_SYMBOL(__fscache_invalidate);

#ifdef CONFIG_PROC_FS
/*
 * Generate a list of extant cookies in /proc/fs/fscache/cookies
 */
static int fscache_cookies_seq_show(struct seq_file *m, void *v)
{
        struct fscache_cookie *cookie;
        unsigned int keylen = 0, auxlen = 0;
        u8 *p;

        if (v == &fscache_cookies) {
                seq_puts(m,
                         "COOKIE   VOLUME   REF ACT ACC S FL DEF             \n"
                         "======== ======== === === === = == ================\n"
                         );
                return 0;
        }

        cookie = list_entry(v, struct fscache_cookie, proc_link);

        seq_printf(m,
                   "%08x %08x %3d %3d %3d %c %02lx",
                   cookie->debug_id,
                   cookie->volume->debug_id,
                   refcount_read(&cookie->ref),
                   atomic_read(&cookie->n_active),
                   atomic_read(&cookie->n_accesses),
                   fscache_cookie_states[cookie->state],
                   cookie->flags);

        keylen = cookie->key_len;
        auxlen = cookie->aux_len;

        if (keylen > 0 || auxlen > 0) {
                seq_puts(m, " ");
                p = keylen <= sizeof(cookie->inline_key) ?
                        cookie->inline_key : cookie->key;
                for (; keylen > 0; keylen--)
                        seq_printf(m, "%02x", *p++);
                if (auxlen > 0) {
                        seq_puts(m, ", ");
                        p = auxlen <= sizeof(cookie->inline_aux) ?
                                cookie->inline_aux : cookie->aux;
                        for (; auxlen > 0; auxlen--)
                                seq_printf(m, "%02x", *p++);
                }
        }

        seq_puts(m, "\n");
        return 0;
}

static void *fscache_cookies_seq_start(struct seq_file *m, loff_t *_pos)
        __acquires(fscache_cookies_lock)
{
        read_lock(&fscache_cookies_lock);
        return seq_list_start_head(&fscache_cookies, *_pos);
}

static void *fscache_cookies_seq_next(struct seq_file *m, void *v, loff_t *_pos)
{
        return seq_list_next(v, &fscache_cookies, _pos);
}

static void fscache_cookies_seq_stop(struct seq_file *m, void *v)
        __releases(rcu)
{
        read_unlock(&fscache_cookies_lock);
}


const struct seq_operations fscache_cookies_seq_ops = {
        .start  = fscache_cookies_seq_start,
        .next   = fscache_cookies_seq_next,
        .stop   = fscache_cookies_seq_stop,
        .show   = fscache_cookies_seq_show,
};
#endif