WIP FPC-III support

[linux/fpc-iii.git] / fs / nfs / nfs42xattr.c

// SPDX-License-Identifier: GPL-2.0

/*
 * Copyright 2019, 2020 Amazon.com, Inc. or its affiliates. All rights reserved.
 *
 * User extended attribute client side cache functions.
 *
 * Author: Frank van der Linden <fllinden@amazon.com>
 */
#include <linux/errno.h>
#include <linux/nfs_fs.h>
#include <linux/hashtable.h>
#include <linux/refcount.h>
#include <uapi/linux/xattr.h>

#include "nfs4_fs.h"
#include "internal.h"

/*
 * User extended attributes client side caching is implemented by having
 * a cache structure attached to NFS inodes. This structure is allocated
 * when needed, and freed when the cache is zapped.
 *
 * The cache structure contains as hash table of entries, and a pointer
 * to a special-cased entry for the listxattr cache.
 *
 * Accessing and allocating / freeing the caches is done via reference
 * counting. The cache entries use a similar refcounting scheme.
 *
 * This makes freeing a cache, both from the shrinker and from the
 * zap cache path, easy. It also means that, in current use cases,
 * the large majority of inodes will not waste any memory, as they
 * will never have any user extended attributes assigned to them.
 *
 * Attribute entries are hashed in to a simple hash table. They are
 * also part of an LRU.
 *
 * There are three shrinkers.
 *
 * Two shrinkers deal with the cache entries themselves: one for
 * large entries (> PAGE_SIZE), and one for smaller entries. The
 * shrinker for the larger entries works more aggressively than
 * those for the smaller entries.
 *
 * The other shrinker frees the cache structures themselves.
 */

/*
 * 64 buckets is a good default. There is likely no reasonable
 * workload that uses more than even 64 user extended attributes.
 * You can certainly add a lot more - but you get what you ask for
 * in those circumstances.
 */
#define NFS4_XATTR_HASH_SIZE    64

#define NFSDBG_FACILITY NFSDBG_XATTRCACHE

struct nfs4_xattr_cache;
struct nfs4_xattr_entry;

struct nfs4_xattr_bucket {
        spinlock_t lock;
        struct hlist_head hlist;
        struct nfs4_xattr_cache *cache;
        bool draining;
};

struct nfs4_xattr_cache {
        struct kref ref;
        struct nfs4_xattr_bucket buckets[NFS4_XATTR_HASH_SIZE];
        struct list_head lru;
        struct list_head dispose;
        atomic_long_t nent;
        spinlock_t listxattr_lock;
        struct inode *inode;
        struct nfs4_xattr_entry *listxattr;
};

struct nfs4_xattr_entry {
        struct kref ref;
        struct hlist_node hnode;
        struct list_head lru;
        struct list_head dispose;
        char *xattr_name;
        void *xattr_value;
        size_t xattr_size;
        struct nfs4_xattr_bucket *bucket;
        uint32_t flags;
};

#define NFS4_XATTR_ENTRY_EXTVAL 0x0001

/*
 * LRU list of NFS inodes that have xattr caches.
 */
static struct list_lru nfs4_xattr_cache_lru;
static struct list_lru nfs4_xattr_entry_lru;
static struct list_lru nfs4_xattr_large_entry_lru;

static struct kmem_cache *nfs4_xattr_cache_cachep;

/*
 * Hashing helper functions.
 */
static void
nfs4_xattr_hash_init(struct nfs4_xattr_cache *cache)
{
        unsigned int i;

        for (i = 0; i < NFS4_XATTR_HASH_SIZE; i++) {
                INIT_HLIST_HEAD(&cache->buckets[i].hlist);
                spin_lock_init(&cache->buckets[i].lock);
                cache->buckets[i].cache = cache;
                cache->buckets[i].draining = false;
        }
}

/*
 * Locking order:
 * 1. inode i_lock or bucket lock
 * 2. list_lru lock (taken by list_lru_* functions)
 */

/*
 * Wrapper functions to add a cache entry to the right LRU.
 */
static bool
nfs4_xattr_entry_lru_add(struct nfs4_xattr_entry *entry)
{
        struct list_lru *lru;

        lru = (entry->flags & NFS4_XATTR_ENTRY_EXTVAL) ?
            &nfs4_xattr_large_entry_lru : &nfs4_xattr_entry_lru;

        return list_lru_add(lru, &entry->lru);
}

static bool
nfs4_xattr_entry_lru_del(struct nfs4_xattr_entry *entry)
{
        struct list_lru *lru;

        lru = (entry->flags & NFS4_XATTR_ENTRY_EXTVAL) ?
            &nfs4_xattr_large_entry_lru : &nfs4_xattr_entry_lru;

        return list_lru_del(lru, &entry->lru);
}

/*
 * This function allocates cache entries. They are the normal
 * extended attribute name/value pairs, but may also be a listxattr
 * cache. Those allocations use the same entry so that they can be
 * treated as one by the memory shrinker.
 *
 * xattr cache entries are allocated together with names. If the
 * value fits in to one page with the entry structure and the name,
 * it will also be part of the same allocation (kmalloc). This is
 * expected to be the vast majority of cases. Larger allocations
 * have a value pointer that is allocated separately by kvmalloc.
 *
 * Parameters:
 *
 * @name:  Name of the extended attribute. NULL for listxattr cache
 *         entry.
 * @value: Value of attribute, or listxattr cache. NULL if the
 *         value is to be copied from pages instead.
 * @pages: Pages to copy the value from, if not NULL. Passed in to
 *         make it easier to copy the value after an RPC, even if
 *         the value will not be passed up to application (e.g.
 *         for a 'query' getxattr with NULL buffer).
 * @len:   Length of the value. Can be 0 for zero-length attribues.
 *         @value and @pages will be NULL if @len is 0.
 */
static struct nfs4_xattr_entry *
nfs4_xattr_alloc_entry(const char *name, const void *value,
                       struct page **pages, size_t len)
{
        struct nfs4_xattr_entry *entry;
        void *valp;
        char *namep;
        size_t alloclen, slen;
        char *buf;
        uint32_t flags;

        BUILD_BUG_ON(sizeof(struct nfs4_xattr_entry) +
            XATTR_NAME_MAX + 1 > PAGE_SIZE);

        alloclen = sizeof(struct nfs4_xattr_entry);
        if (name != NULL) {
                slen = strlen(name) + 1;
                alloclen += slen;
        } else
                slen = 0;

        if (alloclen + len <= PAGE_SIZE) {
                alloclen += len;
                flags = 0;
        } else {
                flags = NFS4_XATTR_ENTRY_EXTVAL;
        }

        buf = kmalloc(alloclen, GFP_KERNEL_ACCOUNT | GFP_NOFS);
        if (buf == NULL)
                return NULL;
        entry = (struct nfs4_xattr_entry *)buf;

        if (name != NULL) {
                namep = buf + sizeof(struct nfs4_xattr_entry);
                memcpy(namep, name, slen);
        } else {
                namep = NULL;
        }


        if (flags & NFS4_XATTR_ENTRY_EXTVAL) {
                valp = kvmalloc(len, GFP_KERNEL_ACCOUNT | GFP_NOFS);
                if (valp == NULL) {
                        kfree(buf);
                        return NULL;
                }
        } else if (len != 0) {
                valp = buf + sizeof(struct nfs4_xattr_entry) + slen;
        } else
                valp = NULL;

        if (valp != NULL) {
                if (value != NULL)
                        memcpy(valp, value, len);
                else
                        _copy_from_pages(valp, pages, 0, len);
        }

        entry->flags = flags;
        entry->xattr_value = valp;
        kref_init(&entry->ref);
        entry->xattr_name = namep;
        entry->xattr_size = len;
        entry->bucket = NULL;
        INIT_LIST_HEAD(&entry->lru);
        INIT_LIST_HEAD(&entry->dispose);
        INIT_HLIST_NODE(&entry->hnode);

        return entry;
}

static void
nfs4_xattr_free_entry(struct nfs4_xattr_entry *entry)
{
        if (entry->flags & NFS4_XATTR_ENTRY_EXTVAL)
                kvfree(entry->xattr_value);
        kfree(entry);
}

static void
nfs4_xattr_free_entry_cb(struct kref *kref)
{
        struct nfs4_xattr_entry *entry;

        entry = container_of(kref, struct nfs4_xattr_entry, ref);

        if (WARN_ON(!list_empty(&entry->lru)))
                return;

        nfs4_xattr_free_entry(entry);
}

static void
nfs4_xattr_free_cache_cb(struct kref *kref)
{
        struct nfs4_xattr_cache *cache;
        int i;

        cache = container_of(kref, struct nfs4_xattr_cache, ref);

        for (i = 0; i < NFS4_XATTR_HASH_SIZE; i++) {
                if (WARN_ON(!hlist_empty(&cache->buckets[i].hlist)))
                        return;
                cache->buckets[i].draining = false;
        }

        cache->listxattr = NULL;

        kmem_cache_free(nfs4_xattr_cache_cachep, cache);

}

static struct nfs4_xattr_cache *
nfs4_xattr_alloc_cache(void)
{
        struct nfs4_xattr_cache *cache;

        cache = kmem_cache_alloc(nfs4_xattr_cache_cachep,
            GFP_KERNEL_ACCOUNT | GFP_NOFS);
        if (cache == NULL)
                return NULL;

        kref_init(&cache->ref);
        atomic_long_set(&cache->nent, 0);

        return cache;
}

/*
 * Set the listxattr cache, which is a special-cased cache entry.
 * The special value ERR_PTR(-ESTALE) is used to indicate that
 * the cache is being drained - this prevents a new listxattr
 * cache from being added to what is now a stale cache.
 */
static int
nfs4_xattr_set_listcache(struct nfs4_xattr_cache *cache,
                         struct nfs4_xattr_entry *new)
{
        struct nfs4_xattr_entry *old;
        int ret = 1;

        spin_lock(&cache->listxattr_lock);

        old = cache->listxattr;

        if (old == ERR_PTR(-ESTALE)) {
                ret = 0;
                goto out;
        }

        cache->listxattr = new;
        if (new != NULL && new != ERR_PTR(-ESTALE))
                nfs4_xattr_entry_lru_add(new);

        if (old != NULL) {
                nfs4_xattr_entry_lru_del(old);
                kref_put(&old->ref, nfs4_xattr_free_entry_cb);
        }
out:
        spin_unlock(&cache->listxattr_lock);

        return ret;
}

/*
 * Unlink a cache from its parent inode, clearing out an invalid
 * cache. Must be called with i_lock held.
 */
static struct nfs4_xattr_cache *
nfs4_xattr_cache_unlink(struct inode *inode)
{
        struct nfs_inode *nfsi;
        struct nfs4_xattr_cache *oldcache;

        nfsi = NFS_I(inode);

        oldcache = nfsi->xattr_cache;
        if (oldcache != NULL) {
                list_lru_del(&nfs4_xattr_cache_lru, &oldcache->lru);
                oldcache->inode = NULL;
        }
        nfsi->xattr_cache = NULL;
        nfsi->cache_validity &= ~NFS_INO_INVALID_XATTR;

        return oldcache;

}

/*
 * Discard a cache. Called by get_cache() if there was an old,
 * invalid cache. Can also be called from a shrinker callback.
 *
 * The cache is dead, it has already been unlinked from its inode,
 * and no longer appears on the cache LRU list.
 *
 * Mark all buckets as draining, so that no new entries are added. This
 * could still happen in the unlikely, but possible case that another
 * thread had grabbed a reference before it was unlinked from the inode,
 * and is still holding it for an add operation.
 *
 * Remove all entries from the LRU lists, so that there is no longer
 * any way to 'find' this cache. Then, remove the entries from the hash
 * table.
 *
 * At that point, the cache will remain empty and can be freed when the final
 * reference drops, which is very likely the kref_put at the end of
 * this function, or the one called immediately afterwards in the
 * shrinker callback.
 */
static void
nfs4_xattr_discard_cache(struct nfs4_xattr_cache *cache)
{
        unsigned int i;
        struct nfs4_xattr_entry *entry;
        struct nfs4_xattr_bucket *bucket;
        struct hlist_node *n;

        nfs4_xattr_set_listcache(cache, ERR_PTR(-ESTALE));

        for (i = 0; i < NFS4_XATTR_HASH_SIZE; i++) {
                bucket = &cache->buckets[i];

                spin_lock(&bucket->lock);
                bucket->draining = true;
                hlist_for_each_entry_safe(entry, n, &bucket->hlist, hnode) {
                        nfs4_xattr_entry_lru_del(entry);
                        hlist_del_init(&entry->hnode);
                        kref_put(&entry->ref, nfs4_xattr_free_entry_cb);
                }
                spin_unlock(&bucket->lock);
        }

        atomic_long_set(&cache->nent, 0);

        kref_put(&cache->ref, nfs4_xattr_free_cache_cb);
}

/*
 * Get a referenced copy of the cache structure. Avoid doing allocs
 * while holding i_lock. Which means that we do some optimistic allocation,
 * and might have to free the result in rare cases.
 *
 * This function only checks the NFS_INO_INVALID_XATTR cache validity bit
 * and acts accordingly, replacing the cache when needed. For the read case
 * (!add), this means that the caller must make sure that the cache
 * is valid before caling this function. getxattr and listxattr call
 * revalidate_inode to do this. The attribute cache timeout (for the
 * non-delegated case) is expected to be dealt with in the revalidate
 * call.
 */

static struct nfs4_xattr_cache *
nfs4_xattr_get_cache(struct inode *inode, int add)
{
        struct nfs_inode *nfsi;
        struct nfs4_xattr_cache *cache, *oldcache, *newcache;

        nfsi = NFS_I(inode);

        cache = oldcache = NULL;

        spin_lock(&inode->i_lock);

        if (nfsi->cache_validity & NFS_INO_INVALID_XATTR)
                oldcache = nfs4_xattr_cache_unlink(inode);
        else
                cache = nfsi->xattr_cache;

        if (cache != NULL)
                kref_get(&cache->ref);

        spin_unlock(&inode->i_lock);

        if (add && cache == NULL) {
                newcache = NULL;

                cache = nfs4_xattr_alloc_cache();
                if (cache == NULL)
                        goto out;

                spin_lock(&inode->i_lock);
                if (nfsi->cache_validity & NFS_INO_INVALID_XATTR) {
                        /*
                         * The cache was invalidated again. Give up,
                         * since what we want to enter is now likely
                         * outdated anyway.
                         */
                        spin_unlock(&inode->i_lock);
                        kref_put(&cache->ref, nfs4_xattr_free_cache_cb);
                        cache = NULL;
                        goto out;
                }

                /*
                 * Check if someone beat us to it.
                 */
                if (nfsi->xattr_cache != NULL) {
                        newcache = nfsi->xattr_cache;
                        kref_get(&newcache->ref);
                } else {
                        kref_get(&cache->ref);
                        nfsi->xattr_cache = cache;
                        cache->inode = inode;
                        list_lru_add(&nfs4_xattr_cache_lru, &cache->lru);
                }

                spin_unlock(&inode->i_lock);

                /*
                 * If there was a race, throw away the cache we just
                 * allocated, and use the new one allocated by someone
                 * else.
                 */
                if (newcache != NULL) {
                        kref_put(&cache->ref, nfs4_xattr_free_cache_cb);
                        cache = newcache;
                }
        }

out:
        /*
         * Discard the now orphaned old cache.
         */
        if (oldcache != NULL)
                nfs4_xattr_discard_cache(oldcache);

        return cache;
}

static inline struct nfs4_xattr_bucket *
nfs4_xattr_hash_bucket(struct nfs4_xattr_cache *cache, const char *name)
{
        return &cache->buckets[jhash(name, strlen(name), 0) &
            (ARRAY_SIZE(cache->buckets) - 1)];
}

static struct nfs4_xattr_entry *
nfs4_xattr_get_entry(struct nfs4_xattr_bucket *bucket, const char *name)
{
        struct nfs4_xattr_entry *entry;

        entry = NULL;

        hlist_for_each_entry(entry, &bucket->hlist, hnode) {
                if (!strcmp(entry->xattr_name, name))
                        break;
        }

        return entry;
}

static int
nfs4_xattr_hash_add(struct nfs4_xattr_cache *cache,
                    struct nfs4_xattr_entry *entry)
{
        struct nfs4_xattr_bucket *bucket;
        struct nfs4_xattr_entry *oldentry = NULL;
        int ret = 1;

        bucket = nfs4_xattr_hash_bucket(cache, entry->xattr_name);
        entry->bucket = bucket;

        spin_lock(&bucket->lock);

        if (bucket->draining) {
                ret = 0;
                goto out;
        }

        oldentry = nfs4_xattr_get_entry(bucket, entry->xattr_name);
        if (oldentry != NULL) {
                hlist_del_init(&oldentry->hnode);
                nfs4_xattr_entry_lru_del(oldentry);
        } else {
                atomic_long_inc(&cache->nent);
        }

        hlist_add_head(&entry->hnode, &bucket->hlist);
        nfs4_xattr_entry_lru_add(entry);

out:
        spin_unlock(&bucket->lock);

        if (oldentry != NULL)
                kref_put(&oldentry->ref, nfs4_xattr_free_entry_cb);

        return ret;
}

static void
nfs4_xattr_hash_remove(struct nfs4_xattr_cache *cache, const char *name)
{
        struct nfs4_xattr_bucket *bucket;
        struct nfs4_xattr_entry *entry;

        bucket = nfs4_xattr_hash_bucket(cache, name);

        spin_lock(&bucket->lock);

        entry = nfs4_xattr_get_entry(bucket, name);
        if (entry != NULL) {
                hlist_del_init(&entry->hnode);
                nfs4_xattr_entry_lru_del(entry);
                atomic_long_dec(&cache->nent);
        }

        spin_unlock(&bucket->lock);

        if (entry != NULL)
                kref_put(&entry->ref, nfs4_xattr_free_entry_cb);
}

static struct nfs4_xattr_entry *
nfs4_xattr_hash_find(struct nfs4_xattr_cache *cache, const char *name)
{
        struct nfs4_xattr_bucket *bucket;
        struct nfs4_xattr_entry *entry;

        bucket = nfs4_xattr_hash_bucket(cache, name);

        spin_lock(&bucket->lock);

        entry = nfs4_xattr_get_entry(bucket, name);
        if (entry != NULL)
                kref_get(&entry->ref);

        spin_unlock(&bucket->lock);

        return entry;
}

/*
 * Entry point to retrieve an entry from the cache.
 */
ssize_t nfs4_xattr_cache_get(struct inode *inode, const char *name, char *buf,
                         ssize_t buflen)
{
        struct nfs4_xattr_cache *cache;
        struct nfs4_xattr_entry *entry;
        ssize_t ret;

        cache = nfs4_xattr_get_cache(inode, 0);
        if (cache == NULL)
                return -ENOENT;

        ret = 0;
        entry = nfs4_xattr_hash_find(cache, name);

        if (entry != NULL) {
                dprintk("%s: cache hit '%s', len %lu\n", __func__,
                    entry->xattr_name, (unsigned long)entry->xattr_size);
                if (buflen == 0) {
                        /* Length probe only */
                        ret = entry->xattr_size;
                } else if (buflen < entry->xattr_size)
                        ret = -ERANGE;
                else {
                        memcpy(buf, entry->xattr_value, entry->xattr_size);
                        ret = entry->xattr_size;
                }
                kref_put(&entry->ref, nfs4_xattr_free_entry_cb);
        } else {
                dprintk("%s: cache miss '%s'\n", __func__, name);
                ret = -ENOENT;
        }

        kref_put(&cache->ref, nfs4_xattr_free_cache_cb);

        return ret;
}

/*
 * Retrieve a cached list of xattrs from the cache.
 */
ssize_t nfs4_xattr_cache_list(struct inode *inode, char *buf, ssize_t buflen)
{
        struct nfs4_xattr_cache *cache;
        struct nfs4_xattr_entry *entry;
        ssize_t ret;

        cache = nfs4_xattr_get_cache(inode, 0);
        if (cache == NULL)
                return -ENOENT;

        spin_lock(&cache->listxattr_lock);

        entry = cache->listxattr;

        if (entry != NULL && entry != ERR_PTR(-ESTALE)) {
                if (buflen == 0) {
                        /* Length probe only */
                        ret = entry->xattr_size;
                } else if (entry->xattr_size > buflen)
                        ret = -ERANGE;
                else {
                        memcpy(buf, entry->xattr_value, entry->xattr_size);
                        ret = entry->xattr_size;
                }
        } else {
                ret = -ENOENT;
        }

        spin_unlock(&cache->listxattr_lock);

        kref_put(&cache->ref, nfs4_xattr_free_cache_cb);

        return ret;
}

/*
 * Add an xattr to the cache.
 *
 * This also invalidates the xattr list cache.
 */
void nfs4_xattr_cache_add(struct inode *inode, const char *name,
                          const char *buf, struct page **pages, ssize_t buflen)
{
        struct nfs4_xattr_cache *cache;
        struct nfs4_xattr_entry *entry;

        dprintk("%s: add '%s' len %lu\n", __func__,
            name, (unsigned long)buflen);

        cache = nfs4_xattr_get_cache(inode, 1);
        if (cache == NULL)
                return;

        entry = nfs4_xattr_alloc_entry(name, buf, pages, buflen);
        if (entry == NULL)
                goto out;

        (void)nfs4_xattr_set_listcache(cache, NULL);

        if (!nfs4_xattr_hash_add(cache, entry))
                kref_put(&entry->ref, nfs4_xattr_free_entry_cb);

out:
        kref_put(&cache->ref, nfs4_xattr_free_cache_cb);
}


/*
 * Remove an xattr from the cache.
 *
 * This also invalidates the xattr list cache.
 */
void nfs4_xattr_cache_remove(struct inode *inode, const char *name)
{
        struct nfs4_xattr_cache *cache;

        dprintk("%s: remove '%s'\n", __func__, name);

        cache = nfs4_xattr_get_cache(inode, 0);
        if (cache == NULL)
                return;

        (void)nfs4_xattr_set_listcache(cache, NULL);
        nfs4_xattr_hash_remove(cache, name);

        kref_put(&cache->ref, nfs4_xattr_free_cache_cb);
}

/*
 * Cache listxattr output, replacing any possible old one.
 */
void nfs4_xattr_cache_set_list(struct inode *inode, const char *buf,
                               ssize_t buflen)
{
        struct nfs4_xattr_cache *cache;
        struct nfs4_xattr_entry *entry;

        cache = nfs4_xattr_get_cache(inode, 1);
        if (cache == NULL)
                return;

        entry = nfs4_xattr_alloc_entry(NULL, buf, NULL, buflen);
        if (entry == NULL)
                goto out;

        /*
         * This is just there to be able to get to bucket->cache,
         * which is obviously the same for all buckets, so just
         * use bucket 0.
         */
        entry->bucket = &cache->buckets[0];

        if (!nfs4_xattr_set_listcache(cache, entry))
                kref_put(&entry->ref, nfs4_xattr_free_entry_cb);

out:
        kref_put(&cache->ref, nfs4_xattr_free_cache_cb);
}

/*
 * Zap the entire cache. Called when an inode is evicted.
 */
void nfs4_xattr_cache_zap(struct inode *inode)
{
        struct nfs4_xattr_cache *oldcache;

        spin_lock(&inode->i_lock);
        oldcache = nfs4_xattr_cache_unlink(inode);
        spin_unlock(&inode->i_lock);

        if (oldcache)
                nfs4_xattr_discard_cache(oldcache);
}

/*
 * The entry LRU is shrunk more aggressively than the cache LRU,
 * by settings @seeks to 1.
 *
 * Cache structures are freed only when they've become empty, after
 * pruning all but one entry.
 */

static unsigned long nfs4_xattr_cache_count(struct shrinker *shrink,
                                            struct shrink_control *sc);
static unsigned long nfs4_xattr_entry_count(struct shrinker *shrink,
                                            struct shrink_control *sc);
static unsigned long nfs4_xattr_cache_scan(struct shrinker *shrink,
                                           struct shrink_control *sc);
static unsigned long nfs4_xattr_entry_scan(struct shrinker *shrink,
                                           struct shrink_control *sc);

static struct shrinker nfs4_xattr_cache_shrinker = {
        .count_objects  = nfs4_xattr_cache_count,
        .scan_objects   = nfs4_xattr_cache_scan,
        .seeks          = DEFAULT_SEEKS,
        .flags          = SHRINKER_MEMCG_AWARE,
};

static struct shrinker nfs4_xattr_entry_shrinker = {
        .count_objects  = nfs4_xattr_entry_count,
        .scan_objects   = nfs4_xattr_entry_scan,
        .seeks          = DEFAULT_SEEKS,
        .batch          = 512,
        .flags          = SHRINKER_MEMCG_AWARE,
};

static struct shrinker nfs4_xattr_large_entry_shrinker = {
        .count_objects  = nfs4_xattr_entry_count,
        .scan_objects   = nfs4_xattr_entry_scan,
        .seeks          = 1,
        .batch          = 512,
        .flags          = SHRINKER_MEMCG_AWARE,
};

static enum lru_status
cache_lru_isolate(struct list_head *item,
        struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
{
        struct list_head *dispose = arg;
        struct inode *inode;
        struct nfs4_xattr_cache *cache = container_of(item,
            struct nfs4_xattr_cache, lru);

        if (atomic_long_read(&cache->nent) > 1)
                return LRU_SKIP;

        /*
         * If a cache structure is on the LRU list, we know that
         * its inode is valid. Try to lock it to break the link.
         * Since we're inverting the lock order here, only try.
         */
        inode = cache->inode;

        if (!spin_trylock(&inode->i_lock))
                return LRU_SKIP;

        kref_get(&cache->ref);

        cache->inode = NULL;
        NFS_I(inode)->xattr_cache = NULL;
        NFS_I(inode)->cache_validity &= ~NFS_INO_INVALID_XATTR;
        list_lru_isolate(lru, &cache->lru);

        spin_unlock(&inode->i_lock);

        list_add_tail(&cache->dispose, dispose);
        return LRU_REMOVED;
}

static unsigned long
nfs4_xattr_cache_scan(struct shrinker *shrink, struct shrink_control *sc)
{
        LIST_HEAD(dispose);
        unsigned long freed;
        struct nfs4_xattr_cache *cache;

        freed = list_lru_shrink_walk(&nfs4_xattr_cache_lru, sc,
            cache_lru_isolate, &dispose);
        while (!list_empty(&dispose)) {
                cache = list_first_entry(&dispose, struct nfs4_xattr_cache,
                    dispose);
                list_del_init(&cache->dispose);
                nfs4_xattr_discard_cache(cache);
                kref_put(&cache->ref, nfs4_xattr_free_cache_cb);
        }

        return freed;
}


static unsigned long
nfs4_xattr_cache_count(struct shrinker *shrink, struct shrink_control *sc)
{
        unsigned long count;

        count = list_lru_shrink_count(&nfs4_xattr_cache_lru, sc);
        return vfs_pressure_ratio(count);
}

static enum lru_status
entry_lru_isolate(struct list_head *item,
        struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
{
        struct list_head *dispose = arg;
        struct nfs4_xattr_bucket *bucket;
        struct nfs4_xattr_cache *cache;
        struct nfs4_xattr_entry *entry = container_of(item,
            struct nfs4_xattr_entry, lru);

        bucket = entry->bucket;
        cache = bucket->cache;

        /*
         * Unhook the entry from its parent (either a cache bucket
         * or a cache structure if it's a listxattr buf), so that
         * it's no longer found. Then add it to the isolate list,
         * to be freed later.
         *
         * In both cases, we're reverting lock order, so use
         * trylock and skip the entry if we can't get the lock.
         */
        if (entry->xattr_name != NULL) {
                /* Regular cache entry */
                if (!spin_trylock(&bucket->lock))
                        return LRU_SKIP;

                kref_get(&entry->ref);

                hlist_del_init(&entry->hnode);
                atomic_long_dec(&cache->nent);
                list_lru_isolate(lru, &entry->lru);

                spin_unlock(&bucket->lock);
        } else {
                /* Listxattr cache entry */
                if (!spin_trylock(&cache->listxattr_lock))
                        return LRU_SKIP;

                kref_get(&entry->ref);

                cache->listxattr = NULL;
                list_lru_isolate(lru, &entry->lru);

                spin_unlock(&cache->listxattr_lock);
        }

        list_add_tail(&entry->dispose, dispose);
        return LRU_REMOVED;
}

static unsigned long
nfs4_xattr_entry_scan(struct shrinker *shrink, struct shrink_control *sc)
{
        LIST_HEAD(dispose);
        unsigned long freed;
        struct nfs4_xattr_entry *entry;
        struct list_lru *lru;

        lru = (shrink == &nfs4_xattr_large_entry_shrinker) ?
            &nfs4_xattr_large_entry_lru : &nfs4_xattr_entry_lru;

        freed = list_lru_shrink_walk(lru, sc, entry_lru_isolate, &dispose);

        while (!list_empty(&dispose)) {
                entry = list_first_entry(&dispose, struct nfs4_xattr_entry,
                    dispose);
                list_del_init(&entry->dispose);

                /*
                 * Drop two references: the one that we just grabbed
                 * in entry_lru_isolate, and the one that was set
                 * when the entry was first allocated.
                 */
                kref_put(&entry->ref, nfs4_xattr_free_entry_cb);
                kref_put(&entry->ref, nfs4_xattr_free_entry_cb);
        }

        return freed;
}

static unsigned long
nfs4_xattr_entry_count(struct shrinker *shrink, struct shrink_control *sc)
{
        unsigned long count;
        struct list_lru *lru;

        lru = (shrink == &nfs4_xattr_large_entry_shrinker) ?
            &nfs4_xattr_large_entry_lru : &nfs4_xattr_entry_lru;

        count = list_lru_shrink_count(lru, sc);
        return vfs_pressure_ratio(count);
}


static void nfs4_xattr_cache_init_once(void *p)
{
        struct nfs4_xattr_cache *cache = (struct nfs4_xattr_cache *)p;

        spin_lock_init(&cache->listxattr_lock);
        atomic_long_set(&cache->nent, 0);
        nfs4_xattr_hash_init(cache);
        cache->listxattr = NULL;
        INIT_LIST_HEAD(&cache->lru);
        INIT_LIST_HEAD(&cache->dispose);
}

int __init nfs4_xattr_cache_init(void)
{
        int ret = 0;

        nfs4_xattr_cache_cachep = kmem_cache_create("nfs4_xattr_cache_cache",
            sizeof(struct nfs4_xattr_cache), 0,
            (SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD|SLAB_ACCOUNT),
            nfs4_xattr_cache_init_once);
        if (nfs4_xattr_cache_cachep == NULL)
                return -ENOMEM;

        ret = list_lru_init_memcg(&nfs4_xattr_large_entry_lru,
            &nfs4_xattr_large_entry_shrinker);
        if (ret)
                goto out4;

        ret = list_lru_init_memcg(&nfs4_xattr_entry_lru,
            &nfs4_xattr_entry_shrinker);
        if (ret)
                goto out3;

        ret = list_lru_init_memcg(&nfs4_xattr_cache_lru,
            &nfs4_xattr_cache_shrinker);
        if (ret)
                goto out2;

        ret = register_shrinker(&nfs4_xattr_cache_shrinker);
        if (ret)
                goto out1;

        ret = register_shrinker(&nfs4_xattr_entry_shrinker);
        if (ret)
                goto out;

        ret = register_shrinker(&nfs4_xattr_large_entry_shrinker);
        if (!ret)
                return 0;

        unregister_shrinker(&nfs4_xattr_entry_shrinker);
out:
        unregister_shrinker(&nfs4_xattr_cache_shrinker);
out1:
        list_lru_destroy(&nfs4_xattr_cache_lru);
out2:
        list_lru_destroy(&nfs4_xattr_entry_lru);
out3:
        list_lru_destroy(&nfs4_xattr_large_entry_lru);
out4:
        kmem_cache_destroy(nfs4_xattr_cache_cachep);

        return ret;
}

void nfs4_xattr_cache_exit(void)
{
        unregister_shrinker(&nfs4_xattr_large_entry_shrinker);
        unregister_shrinker(&nfs4_xattr_entry_shrinker);
        unregister_shrinker(&nfs4_xattr_cache_shrinker);
        list_lru_destroy(&nfs4_xattr_large_entry_lru);
        list_lru_destroy(&nfs4_xattr_entry_lru);
        list_lru_destroy(&nfs4_xattr_cache_lru);
        kmem_cache_destroy(nfs4_xattr_cache_cachep);
}