nfsd: Containerise filecache laundrette

[mirror_ubuntu-focal-kernel.git] / fs / nfsd / filecache.c

/*
 * Open file cache.
 *
 * (c) 2015 - Jeff Layton <jeff.layton@primarydata.com>
 */

#include <linux/hash.h>
#include <linux/slab.h>
#include <linux/file.h>
#include <linux/sched.h>
#include <linux/list_lru.h>
#include <linux/fsnotify_backend.h>
#include <linux/fsnotify.h>
#include <linux/seq_file.h>

#include "vfs.h"
#include "nfsd.h"
#include "nfsfh.h"
#include "netns.h"
#include "filecache.h"
#include "trace.h"

#define NFSDDBG_FACILITY        NFSDDBG_FH

/* FIXME: dynamically size this for the machine somehow? */
#define NFSD_FILE_HASH_BITS                   12
#define NFSD_FILE_HASH_SIZE                  (1 << NFSD_FILE_HASH_BITS)
#define NFSD_LAUNDRETTE_DELAY                (2 * HZ)

#define NFSD_FILE_LRU_RESCAN                 (0)
#define NFSD_FILE_SHUTDOWN                   (1)
#define NFSD_FILE_LRU_THRESHOLD              (4096UL)
#define NFSD_FILE_LRU_LIMIT                  (NFSD_FILE_LRU_THRESHOLD << 2)

/* We only care about NFSD_MAY_READ/WRITE for this cache */
#define NFSD_FILE_MAY_MASK      (NFSD_MAY_READ|NFSD_MAY_WRITE)

struct nfsd_fcache_bucket {
        struct hlist_head       nfb_head;
        spinlock_t              nfb_lock;
        unsigned int            nfb_count;
        unsigned int            nfb_maxcount;
};

static DEFINE_PER_CPU(unsigned long, nfsd_file_cache_hits);

struct nfsd_fcache_disposal {
        struct list_head list;
        struct work_struct work;
        struct net *net;
        spinlock_t lock;
        struct list_head freeme;
        struct rcu_head rcu;
};

struct workqueue_struct *nfsd_filecache_wq __read_mostly;

static struct kmem_cache                *nfsd_file_slab;
static struct kmem_cache                *nfsd_file_mark_slab;
static struct nfsd_fcache_bucket        *nfsd_file_hashtbl;
static struct list_lru                  nfsd_file_lru;
static long                             nfsd_file_lru_flags;
static struct fsnotify_group            *nfsd_file_fsnotify_group;
static atomic_long_t                    nfsd_filecache_count;
static struct delayed_work              nfsd_filecache_laundrette;
static DEFINE_SPINLOCK(laundrette_lock);
static LIST_HEAD(laundrettes);

static void nfsd_file_gc(void);

static void
nfsd_file_schedule_laundrette(void)
{
        long count = atomic_long_read(&nfsd_filecache_count);

        if (count == 0 || test_bit(NFSD_FILE_SHUTDOWN, &nfsd_file_lru_flags))
                return;

        queue_delayed_work(system_wq, &nfsd_filecache_laundrette,
                        NFSD_LAUNDRETTE_DELAY);
}

static void
nfsd_file_slab_free(struct rcu_head *rcu)
{
        struct nfsd_file *nf = container_of(rcu, struct nfsd_file, nf_rcu);

        put_cred(nf->nf_cred);
        kmem_cache_free(nfsd_file_slab, nf);
}

static void
nfsd_file_mark_free(struct fsnotify_mark *mark)
{
        struct nfsd_file_mark *nfm = container_of(mark, struct nfsd_file_mark,
                                                  nfm_mark);

        kmem_cache_free(nfsd_file_mark_slab, nfm);
}

static struct nfsd_file_mark *
nfsd_file_mark_get(struct nfsd_file_mark *nfm)
{
        if (!atomic_inc_not_zero(&nfm->nfm_ref))
                return NULL;
        return nfm;
}

static void
nfsd_file_mark_put(struct nfsd_file_mark *nfm)
{
        if (atomic_dec_and_test(&nfm->nfm_ref)) {

                fsnotify_destroy_mark(&nfm->nfm_mark, nfsd_file_fsnotify_group);
                fsnotify_put_mark(&nfm->nfm_mark);
        }
}

static struct nfsd_file_mark *
nfsd_file_mark_find_or_create(struct nfsd_file *nf)
{
        int                     err;
        struct fsnotify_mark    *mark;
        struct nfsd_file_mark   *nfm = NULL, *new;
        struct inode *inode = nf->nf_inode;

        do {
                mutex_lock(&nfsd_file_fsnotify_group->mark_mutex);
                mark = fsnotify_find_mark(&inode->i_fsnotify_marks,
                                nfsd_file_fsnotify_group);
                if (mark) {
                        nfm = nfsd_file_mark_get(container_of(mark,
                                                 struct nfsd_file_mark,
                                                 nfm_mark));
                        mutex_unlock(&nfsd_file_fsnotify_group->mark_mutex);
                        if (nfm) {
                                fsnotify_put_mark(mark);
                                break;
                        }
                        /* Avoid soft lockup race with nfsd_file_mark_put() */
                        fsnotify_destroy_mark(mark, nfsd_file_fsnotify_group);
                        fsnotify_put_mark(mark);
                } else
                        mutex_unlock(&nfsd_file_fsnotify_group->mark_mutex);

                /* allocate a new nfm */
                new = kmem_cache_alloc(nfsd_file_mark_slab, GFP_KERNEL);
                if (!new)
                        return NULL;
                fsnotify_init_mark(&new->nfm_mark, nfsd_file_fsnotify_group);
                new->nfm_mark.mask = FS_ATTRIB|FS_DELETE_SELF;
                atomic_set(&new->nfm_ref, 1);

                err = fsnotify_add_inode_mark(&new->nfm_mark, inode, 0);

                /*
                 * If the add was successful, then return the object.
                 * Otherwise, we need to put the reference we hold on the
                 * nfm_mark. The fsnotify code will take a reference and put
                 * it on failure, so we can't just free it directly. It's also
                 * not safe to call fsnotify_destroy_mark on it as the
                 * mark->group will be NULL. Thus, we can't let the nfm_ref
                 * counter drive the destruction at this point.
                 */
                if (likely(!err))
                        nfm = new;
                else
                        fsnotify_put_mark(&new->nfm_mark);
        } while (unlikely(err == -EEXIST));

        return nfm;
}

static struct nfsd_file *
nfsd_file_alloc(struct inode *inode, unsigned int may, unsigned int hashval,
                struct net *net)
{
        struct nfsd_file *nf;

        nf = kmem_cache_alloc(nfsd_file_slab, GFP_KERNEL);
        if (nf) {
                INIT_HLIST_NODE(&nf->nf_node);
                INIT_LIST_HEAD(&nf->nf_lru);
                nf->nf_file = NULL;
                nf->nf_cred = get_current_cred();
                nf->nf_net = net;
                nf->nf_flags = 0;
                nf->nf_inode = inode;
                nf->nf_hashval = hashval;
                atomic_set(&nf->nf_ref, 1);
                nf->nf_may = may & NFSD_FILE_MAY_MASK;
                if (may & NFSD_MAY_NOT_BREAK_LEASE) {
                        if (may & NFSD_MAY_WRITE)
                                __set_bit(NFSD_FILE_BREAK_WRITE, &nf->nf_flags);
                        if (may & NFSD_MAY_READ)
                                __set_bit(NFSD_FILE_BREAK_READ, &nf->nf_flags);
                }
                nf->nf_mark = NULL;
                trace_nfsd_file_alloc(nf);
        }
        return nf;
}

static bool
nfsd_file_free(struct nfsd_file *nf)
{
        bool flush = false;

        trace_nfsd_file_put_final(nf);
        if (nf->nf_mark)
                nfsd_file_mark_put(nf->nf_mark);
        if (nf->nf_file) {
                get_file(nf->nf_file);
                filp_close(nf->nf_file, NULL);
                fput(nf->nf_file);
                flush = true;
        }
        call_rcu(&nf->nf_rcu, nfsd_file_slab_free);
        return flush;
}

static bool
nfsd_file_check_writeback(struct nfsd_file *nf)
{
        struct file *file = nf->nf_file;
        struct address_space *mapping;

        if (!file || !(file->f_mode & FMODE_WRITE))
                return false;
        mapping = file->f_mapping;
        return mapping_tagged(mapping, PAGECACHE_TAG_DIRTY) ||
                mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK);
}

static int
nfsd_file_check_write_error(struct nfsd_file *nf)
{
        struct file *file = nf->nf_file;

        if (!file || !(file->f_mode & FMODE_WRITE))
                return 0;
        return filemap_check_wb_err(file->f_mapping, READ_ONCE(file->f_wb_err));
}

static bool
nfsd_file_in_use(struct nfsd_file *nf)
{
        return nfsd_file_check_writeback(nf) ||
                        nfsd_file_check_write_error(nf);
}

static void
nfsd_file_do_unhash(struct nfsd_file *nf)
{
        lockdep_assert_held(&nfsd_file_hashtbl[nf->nf_hashval].nfb_lock);

        trace_nfsd_file_unhash(nf);

        if (nfsd_file_check_write_error(nf))
                nfsd_reset_boot_verifier(net_generic(nf->nf_net, nfsd_net_id));
        --nfsd_file_hashtbl[nf->nf_hashval].nfb_count;
        hlist_del_rcu(&nf->nf_node);
        atomic_long_dec(&nfsd_filecache_count);
}

static bool
nfsd_file_unhash(struct nfsd_file *nf)
{
        if (test_and_clear_bit(NFSD_FILE_HASHED, &nf->nf_flags)) {
                nfsd_file_do_unhash(nf);
                if (!list_empty(&nf->nf_lru))
                        list_lru_del(&nfsd_file_lru, &nf->nf_lru);
                return true;
        }
        return false;
}

/*
 * Return true if the file was unhashed.
 */
static bool
nfsd_file_unhash_and_release_locked(struct nfsd_file *nf, struct list_head *dispose)
{
        lockdep_assert_held(&nfsd_file_hashtbl[nf->nf_hashval].nfb_lock);

        trace_nfsd_file_unhash_and_release_locked(nf);
        if (!nfsd_file_unhash(nf))
                return false;
        /* keep final reference for nfsd_file_lru_dispose */
        if (atomic_add_unless(&nf->nf_ref, -1, 1))
                return true;

        list_add(&nf->nf_lru, dispose);
        return true;
}

static int
nfsd_file_put_noref(struct nfsd_file *nf)
{
        int count;
        trace_nfsd_file_put(nf);

        count = atomic_dec_return(&nf->nf_ref);
        if (!count) {
                WARN_ON(test_bit(NFSD_FILE_HASHED, &nf->nf_flags));
                nfsd_file_free(nf);
        }
        return count;
}

void
nfsd_file_put(struct nfsd_file *nf)
{
        bool is_hashed = test_bit(NFSD_FILE_HASHED, &nf->nf_flags) != 0;
        bool unused = !nfsd_file_in_use(nf);

        set_bit(NFSD_FILE_REFERENCED, &nf->nf_flags);
        if (nfsd_file_put_noref(nf) == 1 && is_hashed && unused)
                nfsd_file_schedule_laundrette();
        if (atomic_long_read(&nfsd_filecache_count) >= NFSD_FILE_LRU_LIMIT)
                nfsd_file_gc();
}

struct nfsd_file *
nfsd_file_get(struct nfsd_file *nf)
{
        if (likely(atomic_inc_not_zero(&nf->nf_ref)))
                return nf;
        return NULL;
}

static void
nfsd_file_dispose_list(struct list_head *dispose)
{
        struct nfsd_file *nf;

        while(!list_empty(dispose)) {
                nf = list_first_entry(dispose, struct nfsd_file, nf_lru);
                list_del(&nf->nf_lru);
                nfsd_file_put_noref(nf);
        }
}

static void
nfsd_file_dispose_list_sync(struct list_head *dispose)
{
        bool flush = false;
        struct nfsd_file *nf;

        while(!list_empty(dispose)) {
                nf = list_first_entry(dispose, struct nfsd_file, nf_lru);
                list_del(&nf->nf_lru);
                if (!atomic_dec_and_test(&nf->nf_ref))
                        continue;
                if (nfsd_file_free(nf))
                        flush = true;
        }
        if (flush)
                flush_delayed_fput();
}

static void
nfsd_file_list_remove_disposal(struct list_head *dst,
                struct nfsd_fcache_disposal *l)
{
        spin_lock(&l->lock);
        list_splice_init(&l->freeme, dst);
        spin_unlock(&l->lock);
}

static void
nfsd_file_list_add_disposal(struct list_head *files, struct net *net)
{
        struct nfsd_fcache_disposal *l;

        rcu_read_lock();
        list_for_each_entry_rcu(l, &laundrettes, list) {
                if (l->net == net) {
                        spin_lock(&l->lock);
                        list_splice_tail_init(files, &l->freeme);
                        spin_unlock(&l->lock);
                        queue_work(nfsd_filecache_wq, &l->work);
                        break;
                }
        }
        rcu_read_unlock();
}

static void
nfsd_file_list_add_pernet(struct list_head *dst, struct list_head *src,
                struct net *net)
{
        struct nfsd_file *nf, *tmp;

        list_for_each_entry_safe(nf, tmp, src, nf_lru) {
                if (nf->nf_net == net)
                        list_move_tail(&nf->nf_lru, dst);
        }
}

static void
nfsd_file_dispose_list_delayed(struct list_head *dispose)
{
        LIST_HEAD(list);
        struct nfsd_file *nf;

        while(!list_empty(dispose)) {
                nf = list_first_entry(dispose, struct nfsd_file, nf_lru);
                nfsd_file_list_add_pernet(&list, dispose, nf->nf_net);
                nfsd_file_list_add_disposal(&list, nf->nf_net);
        }
}

/*
 * Note this can deadlock with nfsd_file_cache_purge.
 */
static enum lru_status
nfsd_file_lru_cb(struct list_head *item, struct list_lru_one *lru,
                 spinlock_t *lock, void *arg)
        __releases(lock)
        __acquires(lock)
{
        struct list_head *head = arg;
        struct nfsd_file *nf = list_entry(item, struct nfsd_file, nf_lru);

        /*
         * Do a lockless refcount check. The hashtable holds one reference, so
         * we look to see if anything else has a reference, or if any have
         * been put since the shrinker last ran. Those don't get unhashed and
         * released.
         *
         * Note that in the put path, we set the flag and then decrement the
         * counter. Here we check the counter and then test and clear the flag.
         * That order is deliberate to ensure that we can do this locklessly.
         */
        if (atomic_read(&nf->nf_ref) > 1)
                goto out_skip;

        /*
         * Don't throw out files that are still undergoing I/O or
         * that have uncleared errors pending.
         */
        if (nfsd_file_check_writeback(nf))
                goto out_skip;

        if (test_and_clear_bit(NFSD_FILE_REFERENCED, &nf->nf_flags))
                goto out_rescan;

        if (!test_and_clear_bit(NFSD_FILE_HASHED, &nf->nf_flags))
                goto out_skip;

        list_lru_isolate_move(lru, &nf->nf_lru, head);
        return LRU_REMOVED;
out_rescan:
        set_bit(NFSD_FILE_LRU_RESCAN, &nfsd_file_lru_flags);
out_skip:
        return LRU_SKIP;
}

static unsigned long
nfsd_file_lru_walk_list(struct shrink_control *sc)
{
        LIST_HEAD(head);
        struct nfsd_file *nf;
        unsigned long ret;

        if (sc)
                ret = list_lru_shrink_walk(&nfsd_file_lru, sc,
                                nfsd_file_lru_cb, &head);
        else
                ret = list_lru_walk(&nfsd_file_lru,
                                nfsd_file_lru_cb,
                                &head, LONG_MAX);
        list_for_each_entry(nf, &head, nf_lru) {
                spin_lock(&nfsd_file_hashtbl[nf->nf_hashval].nfb_lock);
                nfsd_file_do_unhash(nf);
                spin_unlock(&nfsd_file_hashtbl[nf->nf_hashval].nfb_lock);
        }
        nfsd_file_dispose_list_delayed(&head);
        return ret;
}

static void
nfsd_file_gc(void)
{
        nfsd_file_lru_walk_list(NULL);
}

static void
nfsd_file_gc_worker(struct work_struct *work)
{
        nfsd_file_gc();
        nfsd_file_schedule_laundrette();
}

static unsigned long
nfsd_file_lru_count(struct shrinker *s, struct shrink_control *sc)
{
        return list_lru_count(&nfsd_file_lru);
}

static unsigned long
nfsd_file_lru_scan(struct shrinker *s, struct shrink_control *sc)
{
        return nfsd_file_lru_walk_list(sc);
}

static struct shrinker  nfsd_file_shrinker = {
        .scan_objects = nfsd_file_lru_scan,
        .count_objects = nfsd_file_lru_count,
        .seeks = 1,
};

static void
__nfsd_file_close_inode(struct inode *inode, unsigned int hashval,
                        struct list_head *dispose)
{
        struct nfsd_file        *nf;
        struct hlist_node       *tmp;

        spin_lock(&nfsd_file_hashtbl[hashval].nfb_lock);
        hlist_for_each_entry_safe(nf, tmp, &nfsd_file_hashtbl[hashval].nfb_head, nf_node) {
                if (inode == nf->nf_inode)
                        nfsd_file_unhash_and_release_locked(nf, dispose);
        }
        spin_unlock(&nfsd_file_hashtbl[hashval].nfb_lock);
}

/**
 * nfsd_file_close_inode_sync - attempt to forcibly close a nfsd_file
 * @inode: inode of the file to attempt to remove
 *
 * Walk the whole hash bucket, looking for any files that correspond to "inode".
 * If any do, then unhash them and put the hashtable reference to them and
 * destroy any that had their last reference put. Also ensure that any of the
 * fputs also have their final __fput done as well.
 */
void
nfsd_file_close_inode_sync(struct inode *inode)
{
        unsigned int            hashval = (unsigned int)hash_long(inode->i_ino,
                                                NFSD_FILE_HASH_BITS);
        LIST_HEAD(dispose);

        __nfsd_file_close_inode(inode, hashval, &dispose);
        trace_nfsd_file_close_inode_sync(inode, hashval, !list_empty(&dispose));
        nfsd_file_dispose_list_sync(&dispose);
}

/**
 * nfsd_file_close_inode_sync - attempt to forcibly close a nfsd_file
 * @inode: inode of the file to attempt to remove
 *
 * Walk the whole hash bucket, looking for any files that correspond to "inode".
 * If any do, then unhash them and put the hashtable reference to them and
 * destroy any that had their last reference put.
 */
static void
nfsd_file_close_inode(struct inode *inode)
{
        unsigned int            hashval = (unsigned int)hash_long(inode->i_ino,
                                                NFSD_FILE_HASH_BITS);
        LIST_HEAD(dispose);

        __nfsd_file_close_inode(inode, hashval, &dispose);
        trace_nfsd_file_close_inode(inode, hashval, !list_empty(&dispose));
        nfsd_file_dispose_list_delayed(&dispose);
}

/**
 * nfsd_file_delayed_close - close unused nfsd_files
 * @work: dummy
 *
 * Walk the LRU list and close any entries that have not been used since
 * the last scan.
 *
 * Note this can deadlock with nfsd_file_cache_purge.
 */
static void
nfsd_file_delayed_close(struct work_struct *work)
{
        LIST_HEAD(head);
        struct nfsd_fcache_disposal *l = container_of(work,
                        struct nfsd_fcache_disposal, work);

        nfsd_file_list_remove_disposal(&head, l);
        nfsd_file_dispose_list(&head);
}

static int
nfsd_file_lease_notifier_call(struct notifier_block *nb, unsigned long arg,
                            void *data)
{
        struct file_lock *fl = data;

        /* Only close files for F_SETLEASE leases */
        if (fl->fl_flags & FL_LEASE)
                nfsd_file_close_inode_sync(file_inode(fl->fl_file));
        return 0;
}

static struct notifier_block nfsd_file_lease_notifier = {
        .notifier_call = nfsd_file_lease_notifier_call,
};

static int
nfsd_file_fsnotify_handle_event(struct fsnotify_group *group,
                                struct inode *inode,
                                u32 mask, const void *data, int data_type,
                                const struct qstr *file_name, u32 cookie,
                                struct fsnotify_iter_info *iter_info)
{
        trace_nfsd_file_fsnotify_handle_event(inode, mask);

        /* Should be no marks on non-regular files */
        if (!S_ISREG(inode->i_mode)) {
                WARN_ON_ONCE(1);
                return 0;
        }

        /* don't close files if this was not the last link */
        if (mask & FS_ATTRIB) {
                if (inode->i_nlink)
                        return 0;
        }

        nfsd_file_close_inode(inode);
        return 0;
}


static const struct fsnotify_ops nfsd_file_fsnotify_ops = {
        .handle_event = nfsd_file_fsnotify_handle_event,
        .free_mark = nfsd_file_mark_free,
};

int
nfsd_file_cache_init(void)
{
        int             ret = -ENOMEM;
        unsigned int    i;

        clear_bit(NFSD_FILE_SHUTDOWN, &nfsd_file_lru_flags);

        if (nfsd_file_hashtbl)
                return 0;

        nfsd_filecache_wq = alloc_workqueue("nfsd_filecache", 0, 0);
        if (!nfsd_filecache_wq)
                goto out;

        nfsd_file_hashtbl = kcalloc(NFSD_FILE_HASH_SIZE,
                                sizeof(*nfsd_file_hashtbl), GFP_KERNEL);
        if (!nfsd_file_hashtbl) {
                pr_err("nfsd: unable to allocate nfsd_file_hashtbl\n");
                goto out_err;
        }

        nfsd_file_slab = kmem_cache_create("nfsd_file",
                                sizeof(struct nfsd_file), 0, 0, NULL);
        if (!nfsd_file_slab) {
                pr_err("nfsd: unable to create nfsd_file_slab\n");
                goto out_err;
        }

        nfsd_file_mark_slab = kmem_cache_create("nfsd_file_mark",
                                        sizeof(struct nfsd_file_mark), 0, 0, NULL);
        if (!nfsd_file_mark_slab) {
                pr_err("nfsd: unable to create nfsd_file_mark_slab\n");
                goto out_err;
        }


        ret = list_lru_init(&nfsd_file_lru);
        if (ret) {
                pr_err("nfsd: failed to init nfsd_file_lru: %d\n", ret);
                goto out_err;
        }

        ret = register_shrinker(&nfsd_file_shrinker);
        if (ret) {
                pr_err("nfsd: failed to register nfsd_file_shrinker: %d\n", ret);
                goto out_lru;
        }

        ret = lease_register_notifier(&nfsd_file_lease_notifier);
        if (ret) {
                pr_err("nfsd: unable to register lease notifier: %d\n", ret);
                goto out_shrinker;
        }

        nfsd_file_fsnotify_group = fsnotify_alloc_group(&nfsd_file_fsnotify_ops);
        if (IS_ERR(nfsd_file_fsnotify_group)) {
                pr_err("nfsd: unable to create fsnotify group: %ld\n",
                        PTR_ERR(nfsd_file_fsnotify_group));
                nfsd_file_fsnotify_group = NULL;
                goto out_notifier;
        }

        for (i = 0; i < NFSD_FILE_HASH_SIZE; i++) {
                INIT_HLIST_HEAD(&nfsd_file_hashtbl[i].nfb_head);
                spin_lock_init(&nfsd_file_hashtbl[i].nfb_lock);
        }

        INIT_DELAYED_WORK(&nfsd_filecache_laundrette, nfsd_file_gc_worker);
out:
        return ret;
out_notifier:
        lease_unregister_notifier(&nfsd_file_lease_notifier);
out_shrinker:
        unregister_shrinker(&nfsd_file_shrinker);
out_lru:
        list_lru_destroy(&nfsd_file_lru);
out_err:
        kmem_cache_destroy(nfsd_file_slab);
        nfsd_file_slab = NULL;
        kmem_cache_destroy(nfsd_file_mark_slab);
        nfsd_file_mark_slab = NULL;
        kfree(nfsd_file_hashtbl);
        nfsd_file_hashtbl = NULL;
        destroy_workqueue(nfsd_filecache_wq);
        nfsd_filecache_wq = NULL;
        goto out;
}

/*
 * Note this can deadlock with nfsd_file_lru_cb.
 */
void
nfsd_file_cache_purge(struct net *net)
{
        unsigned int            i;
        struct nfsd_file        *nf;
        struct hlist_node       *next;
        LIST_HEAD(dispose);
        bool del;

        if (!nfsd_file_hashtbl)
                return;

        for (i = 0; i < NFSD_FILE_HASH_SIZE; i++) {
                struct nfsd_fcache_bucket *nfb = &nfsd_file_hashtbl[i];

                spin_lock(&nfb->nfb_lock);
                hlist_for_each_entry_safe(nf, next, &nfb->nfb_head, nf_node) {
                        if (net && nf->nf_net != net)
                                continue;
                        del = nfsd_file_unhash_and_release_locked(nf, &dispose);

                        /*
                         * Deadlock detected! Something marked this entry as
                         * unhased, but hasn't removed it from the hash list.
                         */
                        WARN_ON_ONCE(!del);
                }
                spin_unlock(&nfb->nfb_lock);
                nfsd_file_dispose_list(&dispose);
        }
}

static struct nfsd_fcache_disposal *
nfsd_alloc_fcache_disposal(struct net *net)
{
        struct nfsd_fcache_disposal *l;

        l = kmalloc(sizeof(*l), GFP_KERNEL);
        if (!l)
                return NULL;
        INIT_WORK(&l->work, nfsd_file_delayed_close);
        l->net = net;
        spin_lock_init(&l->lock);
        INIT_LIST_HEAD(&l->freeme);
        return l;
}

static void
nfsd_free_fcache_disposal(struct nfsd_fcache_disposal *l)
{
        rcu_assign_pointer(l->net, NULL);
        cancel_work_sync(&l->work);
        nfsd_file_dispose_list(&l->freeme);
        kfree_rcu(l, rcu);
}

static void
nfsd_add_fcache_disposal(struct nfsd_fcache_disposal *l)
{
        spin_lock(&laundrette_lock);
        list_add_tail_rcu(&l->list, &laundrettes);
        spin_unlock(&laundrette_lock);
}

static void
nfsd_del_fcache_disposal(struct nfsd_fcache_disposal *l)
{
        spin_lock(&laundrette_lock);
        list_del_rcu(&l->list);
        spin_unlock(&laundrette_lock);
}

static int
nfsd_alloc_fcache_disposal_net(struct net *net)
{
        struct nfsd_fcache_disposal *l;

        l = nfsd_alloc_fcache_disposal(net);
        if (!l)
                return -ENOMEM;
        nfsd_add_fcache_disposal(l);
        return 0;
}

static void
nfsd_free_fcache_disposal_net(struct net *net)
{
        struct nfsd_fcache_disposal *l;

        rcu_read_lock();
        list_for_each_entry_rcu(l, &laundrettes, list) {
                if (l->net != net)
                        continue;
                nfsd_del_fcache_disposal(l);
                rcu_read_unlock();
                nfsd_free_fcache_disposal(l);
                return;
        }
        rcu_read_unlock();
}

int
nfsd_file_cache_start_net(struct net *net)
{
        return nfsd_alloc_fcache_disposal_net(net);
}

void
nfsd_file_cache_shutdown_net(struct net *net)
{
        nfsd_file_cache_purge(net);
        nfsd_free_fcache_disposal_net(net);
}

void
nfsd_file_cache_shutdown(void)
{
        LIST_HEAD(dispose);

        set_bit(NFSD_FILE_SHUTDOWN, &nfsd_file_lru_flags);

        lease_unregister_notifier(&nfsd_file_lease_notifier);
        unregister_shrinker(&nfsd_file_shrinker);
        /*
         * make sure all callers of nfsd_file_lru_cb are done before
         * calling nfsd_file_cache_purge
         */
        cancel_delayed_work_sync(&nfsd_filecache_laundrette);
        nfsd_file_cache_purge(NULL);
        list_lru_destroy(&nfsd_file_lru);
        rcu_barrier();
        fsnotify_put_group(nfsd_file_fsnotify_group);
        nfsd_file_fsnotify_group = NULL;
        kmem_cache_destroy(nfsd_file_slab);
        nfsd_file_slab = NULL;
        fsnotify_wait_marks_destroyed();
        kmem_cache_destroy(nfsd_file_mark_slab);
        nfsd_file_mark_slab = NULL;
        kfree(nfsd_file_hashtbl);
        nfsd_file_hashtbl = NULL;
        destroy_workqueue(nfsd_filecache_wq);
        nfsd_filecache_wq = NULL;
}

static bool
nfsd_match_cred(const struct cred *c1, const struct cred *c2)
{
        int i;

        if (!uid_eq(c1->fsuid, c2->fsuid))
                return false;
        if (!gid_eq(c1->fsgid, c2->fsgid))
                return false;
        if (c1->group_info == NULL || c2->group_info == NULL)
                return c1->group_info == c2->group_info;
        if (c1->group_info->ngroups != c2->group_info->ngroups)
                return false;
        for (i = 0; i < c1->group_info->ngroups; i++) {
                if (!gid_eq(c1->group_info->gid[i], c2->group_info->gid[i]))
                        return false;
        }
        return true;
}

static struct nfsd_file *
nfsd_file_find_locked(struct inode *inode, unsigned int may_flags,
                        unsigned int hashval, struct net *net)
{
        struct nfsd_file *nf;
        unsigned char need = may_flags & NFSD_FILE_MAY_MASK;

        hlist_for_each_entry_rcu(nf, &nfsd_file_hashtbl[hashval].nfb_head,
                                 nf_node) {
                if ((need & nf->nf_may) != need)
                        continue;
                if (nf->nf_inode != inode)
                        continue;
                if (nf->nf_net != net)
                        continue;
                if (!nfsd_match_cred(nf->nf_cred, current_cred()))
                        continue;
                if (!test_bit(NFSD_FILE_HASHED, &nf->nf_flags))
                        continue;
                if (nfsd_file_get(nf) != NULL)
                        return nf;
        }
        return NULL;
}

/**
 * nfsd_file_is_cached - are there any cached open files for this fh?
 * @inode: inode of the file to check
 *
 * Scan the hashtable for open files that match this fh. Returns true if there
 * are any, and false if not.
 */
bool
nfsd_file_is_cached(struct inode *inode)
{
        bool                    ret = false;
        struct nfsd_file        *nf;
        unsigned int            hashval;

        hashval = (unsigned int)hash_long(inode->i_ino, NFSD_FILE_HASH_BITS);

        rcu_read_lock();
        hlist_for_each_entry_rcu(nf, &nfsd_file_hashtbl[hashval].nfb_head,
                                 nf_node) {
                if (inode == nf->nf_inode) {
                        ret = true;
                        break;
                }
        }
        rcu_read_unlock();
        trace_nfsd_file_is_cached(inode, hashval, (int)ret);
        return ret;
}

__be32
nfsd_file_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp,
                  unsigned int may_flags, struct nfsd_file **pnf)
{
        __be32  status;
        struct net *net = SVC_NET(rqstp);
        struct nfsd_file *nf, *new;
        struct inode *inode;
        unsigned int hashval;
        bool retry = true;

        /* FIXME: skip this if fh_dentry is already set? */
        status = fh_verify(rqstp, fhp, S_IFREG,
                                may_flags|NFSD_MAY_OWNER_OVERRIDE);
        if (status != nfs_ok)
                return status;

        inode = d_inode(fhp->fh_dentry);
        hashval = (unsigned int)hash_long(inode->i_ino, NFSD_FILE_HASH_BITS);
retry:
        rcu_read_lock();
        nf = nfsd_file_find_locked(inode, may_flags, hashval, net);
        rcu_read_unlock();
        if (nf)
                goto wait_for_construction;

        new = nfsd_file_alloc(inode, may_flags, hashval, net);
        if (!new) {
                trace_nfsd_file_acquire(rqstp, hashval, inode, may_flags,
                                        NULL, nfserr_jukebox);
                return nfserr_jukebox;
        }

        spin_lock(&nfsd_file_hashtbl[hashval].nfb_lock);
        nf = nfsd_file_find_locked(inode, may_flags, hashval, net);
        if (nf == NULL)
                goto open_file;
        spin_unlock(&nfsd_file_hashtbl[hashval].nfb_lock);
        nfsd_file_slab_free(&new->nf_rcu);

wait_for_construction:
        wait_on_bit(&nf->nf_flags, NFSD_FILE_PENDING, TASK_UNINTERRUPTIBLE);

        /* Did construction of this file fail? */
        if (!test_bit(NFSD_FILE_HASHED, &nf->nf_flags)) {
                if (!retry) {
                        status = nfserr_jukebox;
                        goto out;
                }
                retry = false;
                nfsd_file_put_noref(nf);
                goto retry;
        }

        this_cpu_inc(nfsd_file_cache_hits);

        if (!(may_flags & NFSD_MAY_NOT_BREAK_LEASE)) {
                bool write = (may_flags & NFSD_MAY_WRITE);

                if (test_bit(NFSD_FILE_BREAK_READ, &nf->nf_flags) ||
                    (test_bit(NFSD_FILE_BREAK_WRITE, &nf->nf_flags) && write)) {
                        status = nfserrno(nfsd_open_break_lease(
                                        file_inode(nf->nf_file), may_flags));
                        if (status == nfs_ok) {
                                clear_bit(NFSD_FILE_BREAK_READ, &nf->nf_flags);
                                if (write)
                                        clear_bit(NFSD_FILE_BREAK_WRITE,
                                                  &nf->nf_flags);
                        }
                }
        }
out:
        if (status == nfs_ok) {
                *pnf = nf;
        } else {
                nfsd_file_put(nf);
                nf = NULL;
        }

        trace_nfsd_file_acquire(rqstp, hashval, inode, may_flags, nf, status);
        return status;
open_file:
        nf = new;
        /* Take reference for the hashtable */
        atomic_inc(&nf->nf_ref);
        __set_bit(NFSD_FILE_HASHED, &nf->nf_flags);
        __set_bit(NFSD_FILE_PENDING, &nf->nf_flags);
        list_lru_add(&nfsd_file_lru, &nf->nf_lru);
        hlist_add_head_rcu(&nf->nf_node, &nfsd_file_hashtbl[hashval].nfb_head);
        ++nfsd_file_hashtbl[hashval].nfb_count;
        nfsd_file_hashtbl[hashval].nfb_maxcount = max(nfsd_file_hashtbl[hashval].nfb_maxcount,
                        nfsd_file_hashtbl[hashval].nfb_count);
        spin_unlock(&nfsd_file_hashtbl[hashval].nfb_lock);
        if (atomic_long_inc_return(&nfsd_filecache_count) >= NFSD_FILE_LRU_THRESHOLD)
                nfsd_file_gc();

        nf->nf_mark = nfsd_file_mark_find_or_create(nf);
        if (nf->nf_mark)
                status = nfsd_open_verified(rqstp, fhp, S_IFREG,
                                may_flags, &nf->nf_file);
        else
                status = nfserr_jukebox;
        /*
         * If construction failed, or we raced with a call to unlink()
         * then unhash.
         */
        if (status != nfs_ok || inode->i_nlink == 0) {
                bool do_free;
                spin_lock(&nfsd_file_hashtbl[hashval].nfb_lock);
                do_free = nfsd_file_unhash(nf);
                spin_unlock(&nfsd_file_hashtbl[hashval].nfb_lock);
                if (do_free)
                        nfsd_file_put_noref(nf);
        }
        clear_bit_unlock(NFSD_FILE_PENDING, &nf->nf_flags);
        smp_mb__after_atomic();
        wake_up_bit(&nf->nf_flags, NFSD_FILE_PENDING);
        goto out;
}

/*
 * Note that fields may be added, removed or reordered in the future. Programs
 * scraping this file for info should test the labels to ensure they're
 * getting the correct field.
 */
static int nfsd_file_cache_stats_show(struct seq_file *m, void *v)
{
        unsigned int i, count = 0, longest = 0;
        unsigned long hits = 0;

        /*
         * No need for spinlocks here since we're not terribly interested in
         * accuracy. We do take the nfsd_mutex simply to ensure that we
         * don't end up racing with server shutdown
         */
        mutex_lock(&nfsd_mutex);
        if (nfsd_file_hashtbl) {
                for (i = 0; i < NFSD_FILE_HASH_SIZE; i++) {
                        count += nfsd_file_hashtbl[i].nfb_count;
                        longest = max(longest, nfsd_file_hashtbl[i].nfb_count);
                }
        }
        mutex_unlock(&nfsd_mutex);

        for_each_possible_cpu(i)
                hits += per_cpu(nfsd_file_cache_hits, i);

        seq_printf(m, "total entries: %u\n", count);
        seq_printf(m, "longest chain: %u\n", longest);
        seq_printf(m, "cache hits:    %lu\n", hits);
        return 0;
}

int nfsd_file_cache_stats_open(struct inode *inode, struct file *file)
{
        return single_open(file, nfsd_file_cache_stats_show, NULL);
}