Linux 4.6-rc6

[cris-mirror.git] / fs / fscache / page.c

/* Cache page management and data I/O routines
 *
 * Copyright (C) 2004-2008 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.
 */

#define FSCACHE_DEBUG_LEVEL PAGE
#include <linux/module.h>
#include <linux/fscache-cache.h>
#include <linux/buffer_head.h>
#include <linux/pagevec.h>
#include <linux/slab.h>
#include "internal.h"

/*
 * check to see if a page is being written to the cache
 */
bool __fscache_check_page_write(struct fscache_cookie *cookie, struct page *page)
{
        void *val;

        rcu_read_lock();
        val = radix_tree_lookup(&cookie->stores, page->index);
        rcu_read_unlock();

        return val != NULL;
}
EXPORT_SYMBOL(__fscache_check_page_write);

/*
 * wait for a page to finish being written to the cache
 */
void __fscache_wait_on_page_write(struct fscache_cookie *cookie, struct page *page)
{
        wait_queue_head_t *wq = bit_waitqueue(&cookie->flags, 0);

        wait_event(*wq, !__fscache_check_page_write(cookie, page));
}
EXPORT_SYMBOL(__fscache_wait_on_page_write);

/*
 * wait for a page to finish being written to the cache. Put a timeout here
 * since we might be called recursively via parent fs.
 */
static
bool release_page_wait_timeout(struct fscache_cookie *cookie, struct page *page)
{
        wait_queue_head_t *wq = bit_waitqueue(&cookie->flags, 0);

        return wait_event_timeout(*wq, !__fscache_check_page_write(cookie, page),
                                  HZ);
}

/*
 * decide whether a page can be released, possibly by cancelling a store to it
 * - we're allowed to sleep if __GFP_DIRECT_RECLAIM is flagged
 */
bool __fscache_maybe_release_page(struct fscache_cookie *cookie,
                                  struct page *page,
                                  gfp_t gfp)
{
        struct page *xpage;
        void *val;

        _enter("%p,%p,%x", cookie, page, gfp);

try_again:
        rcu_read_lock();
        val = radix_tree_lookup(&cookie->stores, page->index);
        if (!val) {
                rcu_read_unlock();
                fscache_stat(&fscache_n_store_vmscan_not_storing);
                __fscache_uncache_page(cookie, page);
                return true;
        }

        /* see if the page is actually undergoing storage - if so we can't get
         * rid of it till the cache has finished with it */
        if (radix_tree_tag_get(&cookie->stores, page->index,
                               FSCACHE_COOKIE_STORING_TAG)) {
                rcu_read_unlock();
                goto page_busy;
        }

        /* the page is pending storage, so we attempt to cancel the store and
         * discard the store request so that the page can be reclaimed */
        spin_lock(&cookie->stores_lock);
        rcu_read_unlock();

        if (radix_tree_tag_get(&cookie->stores, page->index,
                               FSCACHE_COOKIE_STORING_TAG)) {
                /* the page started to undergo storage whilst we were looking,
                 * so now we can only wait or return */
                spin_unlock(&cookie->stores_lock);
                goto page_busy;
        }

        xpage = radix_tree_delete(&cookie->stores, page->index);
        spin_unlock(&cookie->stores_lock);

        if (xpage) {
                fscache_stat(&fscache_n_store_vmscan_cancelled);
                fscache_stat(&fscache_n_store_radix_deletes);
                ASSERTCMP(xpage, ==, page);
        } else {
                fscache_stat(&fscache_n_store_vmscan_gone);
        }

        wake_up_bit(&cookie->flags, 0);
        if (xpage)
                put_page(xpage);
        __fscache_uncache_page(cookie, page);
        return true;

page_busy:
        /* We will wait here if we're allowed to, but that could deadlock the
         * allocator as the work threads writing to the cache may all end up
         * sleeping on memory allocation, so we may need to impose a timeout
         * too. */
        if (!(gfp & __GFP_DIRECT_RECLAIM) || !(gfp & __GFP_FS)) {
                fscache_stat(&fscache_n_store_vmscan_busy);
                return false;
        }

        fscache_stat(&fscache_n_store_vmscan_wait);
        if (!release_page_wait_timeout(cookie, page))
                _debug("fscache writeout timeout page: %p{%lx}",
                        page, page->index);

        gfp &= ~__GFP_DIRECT_RECLAIM;
        goto try_again;
}
EXPORT_SYMBOL(__fscache_maybe_release_page);

/*
 * note that a page has finished being written to the cache
 */
static void fscache_end_page_write(struct fscache_object *object,
                                   struct page *page)
{
        struct fscache_cookie *cookie;
        struct page *xpage = NULL;

        spin_lock(&object->lock);
        cookie = object->cookie;
        if (cookie) {
                /* delete the page from the tree if it is now no longer
                 * pending */
                spin_lock(&cookie->stores_lock);
                radix_tree_tag_clear(&cookie->stores, page->index,
                                     FSCACHE_COOKIE_STORING_TAG);
                if (!radix_tree_tag_get(&cookie->stores, page->index,
                                        FSCACHE_COOKIE_PENDING_TAG)) {
                        fscache_stat(&fscache_n_store_radix_deletes);
                        xpage = radix_tree_delete(&cookie->stores, page->index);
                }
                spin_unlock(&cookie->stores_lock);
                wake_up_bit(&cookie->flags, 0);
        }
        spin_unlock(&object->lock);
        if (xpage)
                put_page(xpage);
}

/*
 * actually apply the changed attributes to a cache object
 */
static void fscache_attr_changed_op(struct fscache_operation *op)
{
        struct fscache_object *object = op->object;
        int ret;

        _enter("{OBJ%x OP%x}", object->debug_id, op->debug_id);

        fscache_stat(&fscache_n_attr_changed_calls);

        if (fscache_object_is_active(object)) {
                fscache_stat(&fscache_n_cop_attr_changed);
                ret = object->cache->ops->attr_changed(object);
                fscache_stat_d(&fscache_n_cop_attr_changed);
                if (ret < 0)
                        fscache_abort_object(object);
        }

        fscache_op_complete(op, true);
        _leave("");
}

/*
 * notification that the attributes on an object have changed
 */
int __fscache_attr_changed(struct fscache_cookie *cookie)
{
        struct fscache_operation *op;
        struct fscache_object *object;
        bool wake_cookie = false;

        _enter("%p", cookie);

        ASSERTCMP(cookie->def->type, !=, FSCACHE_COOKIE_TYPE_INDEX);

        fscache_stat(&fscache_n_attr_changed);

        op = kzalloc(sizeof(*op), GFP_KERNEL);
        if (!op) {
                fscache_stat(&fscache_n_attr_changed_nomem);
                _leave(" = -ENOMEM");
                return -ENOMEM;
        }

        fscache_operation_init(op, fscache_attr_changed_op, NULL, NULL);
        op->flags = FSCACHE_OP_ASYNC |
                (1 << FSCACHE_OP_EXCLUSIVE) |
                (1 << FSCACHE_OP_UNUSE_COOKIE);

        spin_lock(&cookie->lock);

        if (!fscache_cookie_enabled(cookie) ||
            hlist_empty(&cookie->backing_objects))
                goto nobufs;
        object = hlist_entry(cookie->backing_objects.first,
                             struct fscache_object, cookie_link);

        __fscache_use_cookie(cookie);
        if (fscache_submit_exclusive_op(object, op) < 0)
                goto nobufs_dec;
        spin_unlock(&cookie->lock);
        fscache_stat(&fscache_n_attr_changed_ok);
        fscache_put_operation(op);
        _leave(" = 0");
        return 0;

nobufs_dec:
        wake_cookie = __fscache_unuse_cookie(cookie);
nobufs:
        spin_unlock(&cookie->lock);
        fscache_put_operation(op);
        if (wake_cookie)
                __fscache_wake_unused_cookie(cookie);
        fscache_stat(&fscache_n_attr_changed_nobufs);
        _leave(" = %d", -ENOBUFS);
        return -ENOBUFS;
}
EXPORT_SYMBOL(__fscache_attr_changed);

/*
 * Handle cancellation of a pending retrieval op
 */
static void fscache_do_cancel_retrieval(struct fscache_operation *_op)
{
        struct fscache_retrieval *op =
                container_of(_op, struct fscache_retrieval, op);

        atomic_set(&op->n_pages, 0);
}

/*
 * release a retrieval op reference
 */
static void fscache_release_retrieval_op(struct fscache_operation *_op)
{
        struct fscache_retrieval *op =
                container_of(_op, struct fscache_retrieval, op);

        _enter("{OP%x}", op->op.debug_id);

        ASSERTIFCMP(op->op.state != FSCACHE_OP_ST_INITIALISED,
                    atomic_read(&op->n_pages), ==, 0);

        fscache_hist(fscache_retrieval_histogram, op->start_time);
        if (op->context)
                fscache_put_context(op->cookie, op->context);

        _leave("");
}

/*
 * allocate a retrieval op
 */
static struct fscache_retrieval *fscache_alloc_retrieval(
        struct fscache_cookie *cookie,
        struct address_space *mapping,
        fscache_rw_complete_t end_io_func,
        void *context)
{
        struct fscache_retrieval *op;

        /* allocate a retrieval operation and attempt to submit it */
        op = kzalloc(sizeof(*op), GFP_NOIO);
        if (!op) {
                fscache_stat(&fscache_n_retrievals_nomem);
                return NULL;
        }

        fscache_operation_init(&op->op, NULL,
                               fscache_do_cancel_retrieval,
                               fscache_release_retrieval_op);
        op->op.flags    = FSCACHE_OP_MYTHREAD |
                (1UL << FSCACHE_OP_WAITING) |
                (1UL << FSCACHE_OP_UNUSE_COOKIE);
        op->cookie      = cookie;
        op->mapping     = mapping;
        op->end_io_func = end_io_func;
        op->context     = context;
        op->start_time  = jiffies;
        INIT_LIST_HEAD(&op->to_do);

        /* Pin the netfs read context in case we need to do the actual netfs
         * read because we've encountered a cache read failure.
         */
        if (context)
                fscache_get_context(op->cookie, context);
        return op;
}

/*
 * wait for a deferred lookup to complete
 */
int fscache_wait_for_deferred_lookup(struct fscache_cookie *cookie)
{
        unsigned long jif;

        _enter("");

        if (!test_bit(FSCACHE_COOKIE_LOOKING_UP, &cookie->flags)) {
                _leave(" = 0 [imm]");
                return 0;
        }

        fscache_stat(&fscache_n_retrievals_wait);

        jif = jiffies;
        if (wait_on_bit(&cookie->flags, FSCACHE_COOKIE_LOOKING_UP,
                        TASK_INTERRUPTIBLE) != 0) {
                fscache_stat(&fscache_n_retrievals_intr);
                _leave(" = -ERESTARTSYS");
                return -ERESTARTSYS;
        }

        ASSERT(!test_bit(FSCACHE_COOKIE_LOOKING_UP, &cookie->flags));

        smp_rmb();
        fscache_hist(fscache_retrieval_delay_histogram, jif);
        _leave(" = 0 [dly]");
        return 0;
}

/*
 * wait for an object to become active (or dead)
 */
int fscache_wait_for_operation_activation(struct fscache_object *object,
                                          struct fscache_operation *op,
                                          atomic_t *stat_op_waits,
                                          atomic_t *stat_object_dead)
{
        int ret;

        if (!test_bit(FSCACHE_OP_WAITING, &op->flags))
                goto check_if_dead;

        _debug(">>> WT");
        if (stat_op_waits)
                fscache_stat(stat_op_waits);
        if (wait_on_bit(&op->flags, FSCACHE_OP_WAITING,
                        TASK_INTERRUPTIBLE) != 0) {
                ret = fscache_cancel_op(op, false);
                if (ret == 0)
                        return -ERESTARTSYS;

                /* it's been removed from the pending queue by another party,
                 * so we should get to run shortly */
                wait_on_bit(&op->flags, FSCACHE_OP_WAITING,
                            TASK_UNINTERRUPTIBLE);
        }
        _debug("<<< GO");

check_if_dead:
        if (op->state == FSCACHE_OP_ST_CANCELLED) {
                if (stat_object_dead)
                        fscache_stat(stat_object_dead);
                _leave(" = -ENOBUFS [cancelled]");
                return -ENOBUFS;
        }
        if (unlikely(fscache_object_is_dying(object) ||
                     fscache_cache_is_broken(object))) {
                enum fscache_operation_state state = op->state;
                fscache_cancel_op(op, true);
                if (stat_object_dead)
                        fscache_stat(stat_object_dead);
                _leave(" = -ENOBUFS [obj dead %d]", state);
                return -ENOBUFS;
        }
        return 0;
}

/*
 * read a page from the cache or allocate a block in which to store it
 * - we return:
 *   -ENOMEM    - out of memory, nothing done
 *   -ERESTARTSYS - interrupted
 *   -ENOBUFS   - no backing object available in which to cache the block
 *   -ENODATA   - no data available in the backing object for this block
 *   0          - dispatched a read - it'll call end_io_func() when finished
 */
int __fscache_read_or_alloc_page(struct fscache_cookie *cookie,
                                 struct page *page,
                                 fscache_rw_complete_t end_io_func,
                                 void *context,
                                 gfp_t gfp)
{
        struct fscache_retrieval *op;
        struct fscache_object *object;
        bool wake_cookie = false;
        int ret;

        _enter("%p,%p,,,", cookie, page);

        fscache_stat(&fscache_n_retrievals);

        if (hlist_empty(&cookie->backing_objects))
                goto nobufs;

        if (test_bit(FSCACHE_COOKIE_INVALIDATING, &cookie->flags)) {
                _leave(" = -ENOBUFS [invalidating]");
                return -ENOBUFS;
        }

        ASSERTCMP(cookie->def->type, !=, FSCACHE_COOKIE_TYPE_INDEX);
        ASSERTCMP(page, !=, NULL);

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

        op = fscache_alloc_retrieval(cookie, page->mapping,
                                     end_io_func, context);
        if (!op) {
                _leave(" = -ENOMEM");
                return -ENOMEM;
        }
        atomic_set(&op->n_pages, 1);

        spin_lock(&cookie->lock);

        if (!fscache_cookie_enabled(cookie) ||
            hlist_empty(&cookie->backing_objects))
                goto nobufs_unlock;
        object = hlist_entry(cookie->backing_objects.first,
                             struct fscache_object, cookie_link);

        ASSERT(test_bit(FSCACHE_OBJECT_IS_LOOKED_UP, &object->flags));

        __fscache_use_cookie(cookie);
        atomic_inc(&object->n_reads);
        __set_bit(FSCACHE_OP_DEC_READ_CNT, &op->op.flags);

        if (fscache_submit_op(object, &op->op) < 0)
                goto nobufs_unlock_dec;
        spin_unlock(&cookie->lock);

        fscache_stat(&fscache_n_retrieval_ops);

        /* we wait for the operation to become active, and then process it
         * *here*, in this thread, and not in the thread pool */
        ret = fscache_wait_for_operation_activation(
                object, &op->op,
                __fscache_stat(&fscache_n_retrieval_op_waits),
                __fscache_stat(&fscache_n_retrievals_object_dead));
        if (ret < 0)
                goto error;

        /* ask the cache to honour the operation */
        if (test_bit(FSCACHE_COOKIE_NO_DATA_YET, &object->cookie->flags)) {
                fscache_stat(&fscache_n_cop_allocate_page);
                ret = object->cache->ops->allocate_page(op, page, gfp);
                fscache_stat_d(&fscache_n_cop_allocate_page);
                if (ret == 0)
                        ret = -ENODATA;
        } else {
                fscache_stat(&fscache_n_cop_read_or_alloc_page);
                ret = object->cache->ops->read_or_alloc_page(op, page, gfp);
                fscache_stat_d(&fscache_n_cop_read_or_alloc_page);
        }

error:
        if (ret == -ENOMEM)
                fscache_stat(&fscache_n_retrievals_nomem);
        else if (ret == -ERESTARTSYS)
                fscache_stat(&fscache_n_retrievals_intr);
        else if (ret == -ENODATA)
                fscache_stat(&fscache_n_retrievals_nodata);
        else if (ret < 0)
                fscache_stat(&fscache_n_retrievals_nobufs);
        else
                fscache_stat(&fscache_n_retrievals_ok);

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

nobufs_unlock_dec:
        atomic_dec(&object->n_reads);
        wake_cookie = __fscache_unuse_cookie(cookie);
nobufs_unlock:
        spin_unlock(&cookie->lock);
        if (wake_cookie)
                __fscache_wake_unused_cookie(cookie);
        fscache_put_retrieval(op);
nobufs:
        fscache_stat(&fscache_n_retrievals_nobufs);
        _leave(" = -ENOBUFS");
        return -ENOBUFS;
}
EXPORT_SYMBOL(__fscache_read_or_alloc_page);

/*
 * read a list of page from the cache or allocate a block in which to store
 * them
 * - we return:
 *   -ENOMEM    - out of memory, some pages may be being read
 *   -ERESTARTSYS - interrupted, some pages may be being read
 *   -ENOBUFS   - no backing object or space available in which to cache any
 *                pages not being read
 *   -ENODATA   - no data available in the backing object for some or all of
 *                the pages
 *   0          - dispatched a read on all pages
 *
 * end_io_func() will be called for each page read from the cache as it is
 * finishes being read
 *
 * any pages for which a read is dispatched will be removed from pages and
 * nr_pages
 */
int __fscache_read_or_alloc_pages(struct fscache_cookie *cookie,
                                  struct address_space *mapping,
                                  struct list_head *pages,
                                  unsigned *nr_pages,
                                  fscache_rw_complete_t end_io_func,
                                  void *context,
                                  gfp_t gfp)
{
        struct fscache_retrieval *op;
        struct fscache_object *object;
        bool wake_cookie = false;
        int ret;

        _enter("%p,,%d,,,", cookie, *nr_pages);

        fscache_stat(&fscache_n_retrievals);

        if (hlist_empty(&cookie->backing_objects))
                goto nobufs;

        if (test_bit(FSCACHE_COOKIE_INVALIDATING, &cookie->flags)) {
                _leave(" = -ENOBUFS [invalidating]");
                return -ENOBUFS;
        }

        ASSERTCMP(cookie->def->type, !=, FSCACHE_COOKIE_TYPE_INDEX);
        ASSERTCMP(*nr_pages, >, 0);
        ASSERT(!list_empty(pages));

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

        op = fscache_alloc_retrieval(cookie, mapping, end_io_func, context);
        if (!op)
                return -ENOMEM;
        atomic_set(&op->n_pages, *nr_pages);

        spin_lock(&cookie->lock);

        if (!fscache_cookie_enabled(cookie) ||
            hlist_empty(&cookie->backing_objects))
                goto nobufs_unlock;
        object = hlist_entry(cookie->backing_objects.first,
                             struct fscache_object, cookie_link);

        __fscache_use_cookie(cookie);
        atomic_inc(&object->n_reads);
        __set_bit(FSCACHE_OP_DEC_READ_CNT, &op->op.flags);

        if (fscache_submit_op(object, &op->op) < 0)
                goto nobufs_unlock_dec;
        spin_unlock(&cookie->lock);

        fscache_stat(&fscache_n_retrieval_ops);

        /* we wait for the operation to become active, and then process it
         * *here*, in this thread, and not in the thread pool */
        ret = fscache_wait_for_operation_activation(
                object, &op->op,
                __fscache_stat(&fscache_n_retrieval_op_waits),
                __fscache_stat(&fscache_n_retrievals_object_dead));
        if (ret < 0)
                goto error;

        /* ask the cache to honour the operation */
        if (test_bit(FSCACHE_COOKIE_NO_DATA_YET, &object->cookie->flags)) {
                fscache_stat(&fscache_n_cop_allocate_pages);
                ret = object->cache->ops->allocate_pages(
                        op, pages, nr_pages, gfp);
                fscache_stat_d(&fscache_n_cop_allocate_pages);
        } else {
                fscache_stat(&fscache_n_cop_read_or_alloc_pages);
                ret = object->cache->ops->read_or_alloc_pages(
                        op, pages, nr_pages, gfp);
                fscache_stat_d(&fscache_n_cop_read_or_alloc_pages);
        }

error:
        if (ret == -ENOMEM)
                fscache_stat(&fscache_n_retrievals_nomem);
        else if (ret == -ERESTARTSYS)
                fscache_stat(&fscache_n_retrievals_intr);
        else if (ret == -ENODATA)
                fscache_stat(&fscache_n_retrievals_nodata);
        else if (ret < 0)
                fscache_stat(&fscache_n_retrievals_nobufs);
        else
                fscache_stat(&fscache_n_retrievals_ok);

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

nobufs_unlock_dec:
        atomic_dec(&object->n_reads);
        wake_cookie = __fscache_unuse_cookie(cookie);
nobufs_unlock:
        spin_unlock(&cookie->lock);
        fscache_put_retrieval(op);
        if (wake_cookie)
                __fscache_wake_unused_cookie(cookie);
nobufs:
        fscache_stat(&fscache_n_retrievals_nobufs);
        _leave(" = -ENOBUFS");
        return -ENOBUFS;
}
EXPORT_SYMBOL(__fscache_read_or_alloc_pages);

/*
 * allocate a block in the cache on which to store a page
 * - we return:
 *   -ENOMEM    - out of memory, nothing done
 *   -ERESTARTSYS - interrupted
 *   -ENOBUFS   - no backing object available in which to cache the block
 *   0          - block allocated
 */
int __fscache_alloc_page(struct fscache_cookie *cookie,
                         struct page *page,
                         gfp_t gfp)
{
        struct fscache_retrieval *op;
        struct fscache_object *object;
        bool wake_cookie = false;
        int ret;

        _enter("%p,%p,,,", cookie, page);

        fscache_stat(&fscache_n_allocs);

        if (hlist_empty(&cookie->backing_objects))
                goto nobufs;

        ASSERTCMP(cookie->def->type, !=, FSCACHE_COOKIE_TYPE_INDEX);
        ASSERTCMP(page, !=, NULL);

        if (test_bit(FSCACHE_COOKIE_INVALIDATING, &cookie->flags)) {
                _leave(" = -ENOBUFS [invalidating]");
                return -ENOBUFS;
        }

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

        op = fscache_alloc_retrieval(cookie, page->mapping, NULL, NULL);
        if (!op)
                return -ENOMEM;
        atomic_set(&op->n_pages, 1);

        spin_lock(&cookie->lock);

        if (!fscache_cookie_enabled(cookie) ||
            hlist_empty(&cookie->backing_objects))
                goto nobufs_unlock;
        object = hlist_entry(cookie->backing_objects.first,
                             struct fscache_object, cookie_link);

        __fscache_use_cookie(cookie);
        if (fscache_submit_op(object, &op->op) < 0)
                goto nobufs_unlock_dec;
        spin_unlock(&cookie->lock);

        fscache_stat(&fscache_n_alloc_ops);

        ret = fscache_wait_for_operation_activation(
                object, &op->op,
                __fscache_stat(&fscache_n_alloc_op_waits),
                __fscache_stat(&fscache_n_allocs_object_dead));
        if (ret < 0)
                goto error;

        /* ask the cache to honour the operation */
        fscache_stat(&fscache_n_cop_allocate_page);
        ret = object->cache->ops->allocate_page(op, page, gfp);
        fscache_stat_d(&fscache_n_cop_allocate_page);

error:
        if (ret == -ERESTARTSYS)
                fscache_stat(&fscache_n_allocs_intr);
        else if (ret < 0)
                fscache_stat(&fscache_n_allocs_nobufs);
        else
                fscache_stat(&fscache_n_allocs_ok);

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

nobufs_unlock_dec:
        wake_cookie = __fscache_unuse_cookie(cookie);
nobufs_unlock:
        spin_unlock(&cookie->lock);
        fscache_put_retrieval(op);
        if (wake_cookie)
                __fscache_wake_unused_cookie(cookie);
nobufs:
        fscache_stat(&fscache_n_allocs_nobufs);
        _leave(" = -ENOBUFS");
        return -ENOBUFS;
}
EXPORT_SYMBOL(__fscache_alloc_page);

/*
 * Unmark pages allocate in the readahead code path (via:
 * fscache_readpages_or_alloc) after delegating to the base filesystem
 */
void __fscache_readpages_cancel(struct fscache_cookie *cookie,
                                struct list_head *pages)
{
        struct page *page;

        list_for_each_entry(page, pages, lru) {
                if (PageFsCache(page))
                        __fscache_uncache_page(cookie, page);
        }
}
EXPORT_SYMBOL(__fscache_readpages_cancel);

/*
 * release a write op reference
 */
static void fscache_release_write_op(struct fscache_operation *_op)
{
        _enter("{OP%x}", _op->debug_id);
}

/*
 * perform the background storage of a page into the cache
 */
static void fscache_write_op(struct fscache_operation *_op)
{
        struct fscache_storage *op =
                container_of(_op, struct fscache_storage, op);
        struct fscache_object *object = op->op.object;
        struct fscache_cookie *cookie;
        struct page *page;
        unsigned n;
        void *results[1];
        int ret;

        _enter("{OP%x,%d}", op->op.debug_id, atomic_read(&op->op.usage));

        spin_lock(&object->lock);
        cookie = object->cookie;

        if (!fscache_object_is_active(object)) {
                /* If we get here, then the on-disk cache object likely longer
                 * exists, so we should just cancel this write operation.
                 */
                spin_unlock(&object->lock);
                fscache_op_complete(&op->op, false);
                _leave(" [inactive]");
                return;
        }

        if (!cookie) {
                /* If we get here, then the cookie belonging to the object was
                 * detached, probably by the cookie being withdrawn due to
                 * memory pressure, which means that the pages we might write
                 * to the cache from no longer exist - therefore, we can just
                 * cancel this write operation.
                 */
                spin_unlock(&object->lock);
                fscache_op_complete(&op->op, false);
                _leave(" [cancel] op{f=%lx s=%u} obj{s=%s f=%lx}",
                       _op->flags, _op->state, object->state->short_name,
                       object->flags);
                return;
        }

        spin_lock(&cookie->stores_lock);

        fscache_stat(&fscache_n_store_calls);

        /* find a page to store */
        page = NULL;
        n = radix_tree_gang_lookup_tag(&cookie->stores, results, 0, 1,
                                       FSCACHE_COOKIE_PENDING_TAG);
        if (n != 1)
                goto superseded;
        page = results[0];
        _debug("gang %d [%lx]", n, page->index);
        if (page->index >= op->store_limit) {
                fscache_stat(&fscache_n_store_pages_over_limit);
                goto superseded;
        }

        radix_tree_tag_set(&cookie->stores, page->index,
                           FSCACHE_COOKIE_STORING_TAG);
        radix_tree_tag_clear(&cookie->stores, page->index,
                             FSCACHE_COOKIE_PENDING_TAG);

        spin_unlock(&cookie->stores_lock);
        spin_unlock(&object->lock);

        fscache_stat(&fscache_n_store_pages);
        fscache_stat(&fscache_n_cop_write_page);
        ret = object->cache->ops->write_page(op, page);
        fscache_stat_d(&fscache_n_cop_write_page);
        fscache_end_page_write(object, page);
        if (ret < 0) {
                fscache_abort_object(object);
                fscache_op_complete(&op->op, true);
        } else {
                fscache_enqueue_operation(&op->op);
        }

        _leave("");
        return;

superseded:
        /* this writer is going away and there aren't any more things to
         * write */
        _debug("cease");
        spin_unlock(&cookie->stores_lock);
        clear_bit(FSCACHE_OBJECT_PENDING_WRITE, &object->flags);
        spin_unlock(&object->lock);
        fscache_op_complete(&op->op, true);
        _leave("");
}

/*
 * Clear the pages pending writing for invalidation
 */
void fscache_invalidate_writes(struct fscache_cookie *cookie)
{
        struct page *page;
        void *results[16];
        int n, i;

        _enter("");

        for (;;) {
                spin_lock(&cookie->stores_lock);
                n = radix_tree_gang_lookup_tag(&cookie->stores, results, 0,
                                               ARRAY_SIZE(results),
                                               FSCACHE_COOKIE_PENDING_TAG);
                if (n == 0) {
                        spin_unlock(&cookie->stores_lock);
                        break;
                }

                for (i = n - 1; i >= 0; i--) {
                        page = results[i];
                        radix_tree_delete(&cookie->stores, page->index);
                }

                spin_unlock(&cookie->stores_lock);

                for (i = n - 1; i >= 0; i--)
                        put_page(results[i]);
        }

        _leave("");
}

/*
 * request a page be stored in the cache
 * - returns:
 *   -ENOMEM    - out of memory, nothing done
 *   -ENOBUFS   - no backing object available in which to cache the page
 *   0          - dispatched a write - it'll call end_io_func() when finished
 *
 * if the cookie still has a backing object at this point, that object can be
 * in one of a few states with respect to storage processing:
 *
 *  (1) negative lookup, object not yet created (FSCACHE_COOKIE_CREATING is
 *      set)
 *
 *      (a) no writes yet
 *
 *      (b) writes deferred till post-creation (mark page for writing and
 *          return immediately)
 *
 *  (2) negative lookup, object created, initial fill being made from netfs
 *
 *      (a) fill point not yet reached this page (mark page for writing and
 *          return)
 *
 *      (b) fill point passed this page (queue op to store this page)
 *
 *  (3) object extant (queue op to store this page)
 *
 * any other state is invalid
 */
int __fscache_write_page(struct fscache_cookie *cookie,
                         struct page *page,
                         gfp_t gfp)
{
        struct fscache_storage *op;
        struct fscache_object *object;
        bool wake_cookie = false;
        int ret;

        _enter("%p,%x,", cookie, (u32) page->flags);

        ASSERTCMP(cookie->def->type, !=, FSCACHE_COOKIE_TYPE_INDEX);
        ASSERT(PageFsCache(page));

        fscache_stat(&fscache_n_stores);

        if (test_bit(FSCACHE_COOKIE_INVALIDATING, &cookie->flags)) {
                _leave(" = -ENOBUFS [invalidating]");
                return -ENOBUFS;
        }

        op = kzalloc(sizeof(*op), GFP_NOIO | __GFP_NOMEMALLOC | __GFP_NORETRY);
        if (!op)
                goto nomem;

        fscache_operation_init(&op->op, fscache_write_op, NULL,
                               fscache_release_write_op);
        op->op.flags = FSCACHE_OP_ASYNC |
                (1 << FSCACHE_OP_WAITING) |
                (1 << FSCACHE_OP_UNUSE_COOKIE);

        ret = radix_tree_maybe_preload(gfp & ~__GFP_HIGHMEM);
        if (ret < 0)
                goto nomem_free;

        ret = -ENOBUFS;
        spin_lock(&cookie->lock);

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

        /* add the page to the pending-storage radix tree on the backing
         * object */
        spin_lock(&object->lock);
        spin_lock(&cookie->stores_lock);

        _debug("store limit %llx", (unsigned long long) object->store_limit);

        ret = radix_tree_insert(&cookie->stores, page->index, page);
        if (ret < 0) {
                if (ret == -EEXIST)
                        goto already_queued;
                _debug("insert failed %d", ret);
                goto nobufs_unlock_obj;
        }

        radix_tree_tag_set(&cookie->stores, page->index,
                           FSCACHE_COOKIE_PENDING_TAG);
        get_page(page);

        /* we only want one writer at a time, but we do need to queue new
         * writers after exclusive ops */
        if (test_and_set_bit(FSCACHE_OBJECT_PENDING_WRITE, &object->flags))
                goto already_pending;

        spin_unlock(&cookie->stores_lock);
        spin_unlock(&object->lock);

        op->op.debug_id = atomic_inc_return(&fscache_op_debug_id);
        op->store_limit = object->store_limit;

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

        spin_unlock(&cookie->lock);
        radix_tree_preload_end();
        fscache_stat(&fscache_n_store_ops);
        fscache_stat(&fscache_n_stores_ok);

        /* the work queue now carries its own ref on the object */
        fscache_put_operation(&op->op);
        _leave(" = 0");
        return 0;

already_queued:
        fscache_stat(&fscache_n_stores_again);
already_pending:
        spin_unlock(&cookie->stores_lock);
        spin_unlock(&object->lock);
        spin_unlock(&cookie->lock);
        radix_tree_preload_end();
        fscache_put_operation(&op->op);
        fscache_stat(&fscache_n_stores_ok);
        _leave(" = 0");
        return 0;

submit_failed:
        spin_lock(&cookie->stores_lock);
        radix_tree_delete(&cookie->stores, page->index);
        spin_unlock(&cookie->stores_lock);
        wake_cookie = __fscache_unuse_cookie(cookie);
        put_page(page);
        ret = -ENOBUFS;
        goto nobufs;

nobufs_unlock_obj:
        spin_unlock(&cookie->stores_lock);
        spin_unlock(&object->lock);
nobufs:
        spin_unlock(&cookie->lock);
        radix_tree_preload_end();
        fscache_put_operation(&op->op);
        if (wake_cookie)
                __fscache_wake_unused_cookie(cookie);
        fscache_stat(&fscache_n_stores_nobufs);
        _leave(" = -ENOBUFS");
        return -ENOBUFS;

nomem_free:
        fscache_put_operation(&op->op);
nomem:
        fscache_stat(&fscache_n_stores_oom);
        _leave(" = -ENOMEM");
        return -ENOMEM;
}
EXPORT_SYMBOL(__fscache_write_page);

/*
 * remove a page from the cache
 */
void __fscache_uncache_page(struct fscache_cookie *cookie, struct page *page)
{
        struct fscache_object *object;

        _enter(",%p", page);

        ASSERTCMP(cookie->def->type, !=, FSCACHE_COOKIE_TYPE_INDEX);
        ASSERTCMP(page, !=, NULL);

        fscache_stat(&fscache_n_uncaches);

        /* cache withdrawal may beat us to it */
        if (!PageFsCache(page))
                goto done;

        /* get the object */
        spin_lock(&cookie->lock);

        if (hlist_empty(&cookie->backing_objects)) {
                ClearPageFsCache(page);
                goto done_unlock;
        }

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

        /* there might now be stuff on disk we could read */
        clear_bit(FSCACHE_COOKIE_NO_DATA_YET, &cookie->flags);

        /* only invoke the cache backend if we managed to mark the page
         * uncached here; this deals with synchronisation vs withdrawal */
        if (TestClearPageFsCache(page) &&
            object->cache->ops->uncache_page) {
                /* the cache backend releases the cookie lock */
                fscache_stat(&fscache_n_cop_uncache_page);
                object->cache->ops->uncache_page(object, page);
                fscache_stat_d(&fscache_n_cop_uncache_page);
                goto done;
        }

done_unlock:
        spin_unlock(&cookie->lock);
done:
        _leave("");
}
EXPORT_SYMBOL(__fscache_uncache_page);

/**
 * fscache_mark_page_cached - Mark a page as being cached
 * @op: The retrieval op pages are being marked for
 * @page: The page to be marked
 *
 * Mark a netfs page as being cached.  After this is called, the netfs
 * must call fscache_uncache_page() to remove the mark.
 */
void fscache_mark_page_cached(struct fscache_retrieval *op, struct page *page)
{
        struct fscache_cookie *cookie = op->op.object->cookie;

#ifdef CONFIG_FSCACHE_STATS
        atomic_inc(&fscache_n_marks);
#endif

        _debug("- mark %p{%lx}", page, page->index);
        if (TestSetPageFsCache(page)) {
                static bool once_only;
                if (!once_only) {
                        once_only = true;
                        pr_warn("Cookie type %s marked page %lx multiple times\n",
                                cookie->def->name, page->index);
                }
        }

        if (cookie->def->mark_page_cached)
                cookie->def->mark_page_cached(cookie->netfs_data,
                                              op->mapping, page);
}
EXPORT_SYMBOL(fscache_mark_page_cached);

/**
 * fscache_mark_pages_cached - Mark pages as being cached
 * @op: The retrieval op pages are being marked for
 * @pagevec: The pages to be marked
 *
 * Mark a bunch of netfs pages as being cached.  After this is called,
 * the netfs must call fscache_uncache_page() to remove the mark.
 */
void fscache_mark_pages_cached(struct fscache_retrieval *op,
                               struct pagevec *pagevec)
{
        unsigned long loop;

        for (loop = 0; loop < pagevec->nr; loop++)
                fscache_mark_page_cached(op, pagevec->pages[loop]);

        pagevec_reinit(pagevec);
}
EXPORT_SYMBOL(fscache_mark_pages_cached);

/*
 * Uncache all the pages in an inode that are marked PG_fscache, assuming them
 * to be associated with the given cookie.
 */
void __fscache_uncache_all_inode_pages(struct fscache_cookie *cookie,
                                       struct inode *inode)
{
        struct address_space *mapping = inode->i_mapping;
        struct pagevec pvec;
        pgoff_t next;
        int i;

        _enter("%p,%p", cookie, inode);

        if (!mapping || mapping->nrpages == 0) {
                _leave(" [no pages]");
                return;
        }

        pagevec_init(&pvec, 0);
        next = 0;
        do {
                if (!pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE))
                        break;
                for (i = 0; i < pagevec_count(&pvec); i++) {
                        struct page *page = pvec.pages[i];
                        next = page->index;
                        if (PageFsCache(page)) {
                                __fscache_wait_on_page_write(cookie, page);
                                __fscache_uncache_page(cookie, page);
                        }
                }
                pagevec_release(&pvec);
                cond_resched();
        } while (++next);

        _leave("");
}
EXPORT_SYMBOL(__fscache_uncache_all_inode_pages);