Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

[mirror_ubuntu-artful-kernel.git] / drivers / staging / lustre / lustre / llite / statahead.c

/*
 * GPL HEADER START
 *
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 only,
 * as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License version 2 for more details (a copy is included
 * in the LICENSE file that accompanied this code).
 *
 * You should have received a copy of the GNU General Public License
 * version 2 along with this program; If not, see
 * http://www.sun.com/software/products/lustre/docs/GPLv2.pdf
 *
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 *
 * GPL HEADER END
 */
/*
 * Copyright (c) 2008, 2010, Oracle and/or its affiliates. All rights reserved.
 * Use is subject to license terms.
 *
 * Copyright (c) 2011, 2012, Intel Corporation.
 */
/*
 * This file is part of Lustre, http://www.lustre.org/
 * Lustre is a trademark of Sun Microsystems, Inc.
 */

#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>

#define DEBUG_SUBSYSTEM S_LLITE

#include "../include/obd_support.h"
#include "../include/lustre_lite.h"
#include "../include/lustre_dlm.h"
#include "llite_internal.h"

#define SA_OMITTED_ENTRY_MAX 8ULL

typedef enum {
        /** negative values are for error cases */
        SA_ENTRY_INIT = 0,      /** init entry */
        SA_ENTRY_SUCC = 1,      /** stat succeed */
        SA_ENTRY_INVA = 2,      /** invalid entry */
        SA_ENTRY_DEST = 3,      /** entry to be destroyed */
} se_stat_t;

struct ll_sa_entry {
        /* link into sai->sai_entries */
        struct list_head              se_link;
        /* link into sai->sai_entries_{received,stated} */
        struct list_head              se_list;
        /* link into sai hash table locally */
        struct list_head              se_hash;
        /* entry reference count */
        atomic_t            se_refcount;
        /* entry index in the sai */
        __u64              se_index;
        /* low layer ldlm lock handle */
        __u64              se_handle;
        /* entry status */
        se_stat_t              se_stat;
        /* entry size, contains name */
        int                  se_size;
        /* pointer to async getattr enqueue info */
        struct md_enqueue_info *se_minfo;
        /* pointer to the async getattr request */
        struct ptlrpc_request  *se_req;
        /* pointer to the target inode */
        struct inode       *se_inode;
        /* entry name */
        struct qstr          se_qstr;
};

static unsigned int sai_generation;
static DEFINE_SPINLOCK(sai_generation_lock);

static inline int ll_sa_entry_unhashed(struct ll_sa_entry *entry)
{
        return list_empty(&entry->se_hash);
}

/*
 * The entry only can be released by the caller, it is necessary to hold lock.
 */
static inline int ll_sa_entry_stated(struct ll_sa_entry *entry)
{
        smp_rmb();
        return (entry->se_stat != SA_ENTRY_INIT);
}

static inline int ll_sa_entry_hash(int val)
{
        return val & LL_SA_CACHE_MASK;
}

/*
 * Insert entry to hash SA table.
 */
static inline void
ll_sa_entry_enhash(struct ll_statahead_info *sai, struct ll_sa_entry *entry)
{
        int i = ll_sa_entry_hash(entry->se_qstr.hash);

        spin_lock(&sai->sai_cache_lock[i]);
        list_add_tail(&entry->se_hash, &sai->sai_cache[i]);
        spin_unlock(&sai->sai_cache_lock[i]);
}

/*
 * Remove entry from SA table.
 */
static inline void
ll_sa_entry_unhash(struct ll_statahead_info *sai, struct ll_sa_entry *entry)
{
        int i = ll_sa_entry_hash(entry->se_qstr.hash);

        spin_lock(&sai->sai_cache_lock[i]);
        list_del_init(&entry->se_hash);
        spin_unlock(&sai->sai_cache_lock[i]);
}

static inline int agl_should_run(struct ll_statahead_info *sai,
                                 struct inode *inode)
{
        return (inode != NULL && S_ISREG(inode->i_mode) && sai->sai_agl_valid);
}

static inline struct ll_sa_entry *
sa_first_received_entry(struct ll_statahead_info *sai)
{
        return list_entry(sai->sai_entries_received.next,
                              struct ll_sa_entry, se_list);
}

static inline struct ll_inode_info *
agl_first_entry(struct ll_statahead_info *sai)
{
        return list_entry(sai->sai_entries_agl.next,
                              struct ll_inode_info, lli_agl_list);
}

static inline int sa_sent_full(struct ll_statahead_info *sai)
{
        return atomic_read(&sai->sai_cache_count) >= sai->sai_max;
}

static inline int sa_received_empty(struct ll_statahead_info *sai)
{
        return list_empty(&sai->sai_entries_received);
}

static inline int agl_list_empty(struct ll_statahead_info *sai)
{
        return list_empty(&sai->sai_entries_agl);
}

/**
 * (1) hit ratio less than 80%
 * or
 * (2) consecutive miss more than 8
 * then means low hit.
 */
static inline int sa_low_hit(struct ll_statahead_info *sai)
{
        return ((sai->sai_hit > 7 && sai->sai_hit < 4 * sai->sai_miss) ||
                (sai->sai_consecutive_miss > 8));
}

/*
 * If the given index is behind of statahead window more than
 * SA_OMITTED_ENTRY_MAX, then it is old.
 */
static inline int is_omitted_entry(struct ll_statahead_info *sai, __u64 index)
{
        return ((__u64)sai->sai_max + index + SA_OMITTED_ENTRY_MAX <
                 sai->sai_index);
}

/*
 * Insert it into sai_entries tail when init.
 */
static struct ll_sa_entry *
ll_sa_entry_alloc(struct ll_statahead_info *sai, __u64 index,
                  const char *name, int len)
{
        struct ll_inode_info *lli;
        struct ll_sa_entry   *entry;
        int                entry_size;
        char             *dname;

        entry_size = sizeof(struct ll_sa_entry) + (len & ~3) + 4;
        entry = kzalloc(entry_size, GFP_NOFS);
        if (unlikely(!entry))
                return ERR_PTR(-ENOMEM);

        CDEBUG(D_READA, "alloc sa entry %.*s(%p) index %llu\n",
               len, name, entry, index);

        entry->se_index = index;

        /*
         * Statahead entry reference rules:
         *
         * 1) When statahead entry is initialized, its reference is set as 2.
         *    One reference is used by the directory scanner. When the scanner
         *    searches the statahead cache for the given name, it can perform
         *    lockless hash lookup (only the scanner can remove entry from hash
         *    list), and once found, it needn't to call "atomic_inc()" for the
         *    entry reference. So the performance is improved. After using the
         *    statahead entry, the scanner will call "atomic_dec()" to drop the
         *    reference held when initialization. If it is the last reference,
         *    the statahead entry will be freed.
         *
         * 2) All other threads, including statahead thread and ptlrpcd thread,
         *    when they process the statahead entry, the reference for target
         *    should be held to guarantee the entry will not be released by the
         *    directory scanner. After processing the entry, these threads will
         *    drop the entry reference. If it is the last reference, the entry
         *    will be freed.
         *
         *    The second reference when initializes the statahead entry is used
         *    by the statahead thread, following the rule 2).
         */
        atomic_set(&entry->se_refcount, 2);
        entry->se_stat = SA_ENTRY_INIT;
        entry->se_size = entry_size;
        dname = (char *)entry + sizeof(struct ll_sa_entry);
        memcpy(dname, name, len);
        dname[len] = 0;
        entry->se_qstr.hash = full_name_hash(name, len);
        entry->se_qstr.len = len;
        entry->se_qstr.name = dname;

        lli = ll_i2info(sai->sai_inode);
        spin_lock(&lli->lli_sa_lock);
        list_add_tail(&entry->se_link, &sai->sai_entries);
        INIT_LIST_HEAD(&entry->se_list);
        ll_sa_entry_enhash(sai, entry);
        spin_unlock(&lli->lli_sa_lock);

        atomic_inc(&sai->sai_cache_count);

        return entry;
}

/*
 * Used by the directory scanner to search entry with name.
 *
 * Only the caller can remove the entry from hash, so it is unnecessary to hold
 * hash lock. It is caller's duty to release the init refcount on the entry, so
 * it is also unnecessary to increase refcount on the entry.
 */
static struct ll_sa_entry *
ll_sa_entry_get_byname(struct ll_statahead_info *sai, const struct qstr *qstr)
{
        struct ll_sa_entry *entry;
        int i = ll_sa_entry_hash(qstr->hash);

        list_for_each_entry(entry, &sai->sai_cache[i], se_hash) {
                if (entry->se_qstr.hash == qstr->hash &&
                    entry->se_qstr.len == qstr->len &&
                    memcmp(entry->se_qstr.name, qstr->name, qstr->len) == 0)
                        return entry;
        }
        return NULL;
}

/*
 * Used by the async getattr request callback to find entry with index.
 *
 * Inside lli_sa_lock to prevent others to change the list during the search.
 * It needs to increase entry refcount before returning to guarantee that the
 * entry cannot be freed by others.
 */
static struct ll_sa_entry *
ll_sa_entry_get_byindex(struct ll_statahead_info *sai, __u64 index)
{
        struct ll_sa_entry *entry;

        list_for_each_entry(entry, &sai->sai_entries, se_link) {
                if (entry->se_index == index) {
                        LASSERT(atomic_read(&entry->se_refcount) > 0);
                        atomic_inc(&entry->se_refcount);
                        return entry;
                }
                if (entry->se_index > index)
                        break;
        }
        return NULL;
}

static void ll_sa_entry_cleanup(struct ll_statahead_info *sai,
                                 struct ll_sa_entry *entry)
{
        struct md_enqueue_info *minfo = entry->se_minfo;
        struct ptlrpc_request  *req   = entry->se_req;

        if (minfo) {
                entry->se_minfo = NULL;
                ll_intent_release(&minfo->mi_it);
                iput(minfo->mi_dir);
                OBD_FREE_PTR(minfo);
        }

        if (req) {
                entry->se_req = NULL;
                ptlrpc_req_finished(req);
        }
}

static void ll_sa_entry_put(struct ll_statahead_info *sai,
                             struct ll_sa_entry *entry)
{
        if (atomic_dec_and_test(&entry->se_refcount)) {
                CDEBUG(D_READA, "free sa entry %.*s(%p) index %llu\n",
                       entry->se_qstr.len, entry->se_qstr.name, entry,
                       entry->se_index);

                LASSERT(list_empty(&entry->se_link));
                LASSERT(list_empty(&entry->se_list));
                LASSERT(ll_sa_entry_unhashed(entry));

                ll_sa_entry_cleanup(sai, entry);
                iput(entry->se_inode);

                OBD_FREE(entry, entry->se_size);
                atomic_dec(&sai->sai_cache_count);
        }
}

static inline void
do_sa_entry_fini(struct ll_statahead_info *sai, struct ll_sa_entry *entry)
{
        struct ll_inode_info *lli = ll_i2info(sai->sai_inode);

        LASSERT(!ll_sa_entry_unhashed(entry));
        LASSERT(!list_empty(&entry->se_link));

        ll_sa_entry_unhash(sai, entry);

        spin_lock(&lli->lli_sa_lock);
        entry->se_stat = SA_ENTRY_DEST;
        list_del_init(&entry->se_link);
        if (likely(!list_empty(&entry->se_list)))
                list_del_init(&entry->se_list);
        spin_unlock(&lli->lli_sa_lock);

        ll_sa_entry_put(sai, entry);
}

/*
 * Delete it from sai_entries_stated list when fini.
 */
static void
ll_sa_entry_fini(struct ll_statahead_info *sai, struct ll_sa_entry *entry)
{
        struct ll_sa_entry *pos, *next;

        if (entry)
                do_sa_entry_fini(sai, entry);

        /* drop old entry, only 'scanner' process does this, no need to lock */
        list_for_each_entry_safe(pos, next, &sai->sai_entries, se_link) {
                if (!is_omitted_entry(sai, pos->se_index))
                        break;
                do_sa_entry_fini(sai, pos);
        }
}

/*
 * Inside lli_sa_lock.
 */
static void
do_sa_entry_to_stated(struct ll_statahead_info *sai,
                      struct ll_sa_entry *entry, se_stat_t stat)
{
        struct ll_sa_entry *se;
        struct list_head         *pos = &sai->sai_entries_stated;

        if (!list_empty(&entry->se_list))
                list_del_init(&entry->se_list);

        list_for_each_entry_reverse(se, &sai->sai_entries_stated, se_list) {
                if (se->se_index < entry->se_index) {
                        pos = &se->se_list;
                        break;
                }
        }

        list_add(&entry->se_list, pos);
        entry->se_stat = stat;
}

/*
 * Move entry to sai_entries_stated and sort with the index.
 * \retval 1    -- entry to be destroyed.
 * \retval 0    -- entry is inserted into stated list.
 */
static int
ll_sa_entry_to_stated(struct ll_statahead_info *sai,
                      struct ll_sa_entry *entry, se_stat_t stat)
{
        struct ll_inode_info *lli = ll_i2info(sai->sai_inode);
        int                ret = 1;

        ll_sa_entry_cleanup(sai, entry);

        spin_lock(&lli->lli_sa_lock);
        if (likely(entry->se_stat != SA_ENTRY_DEST)) {
                do_sa_entry_to_stated(sai, entry, stat);
                ret = 0;
        }
        spin_unlock(&lli->lli_sa_lock);

        return ret;
}

/*
 * Insert inode into the list of sai_entries_agl.
 */
static void ll_agl_add(struct ll_statahead_info *sai,
                       struct inode *inode, int index)
{
        struct ll_inode_info *child  = ll_i2info(inode);
        struct ll_inode_info *parent = ll_i2info(sai->sai_inode);
        int                added  = 0;

        spin_lock(&child->lli_agl_lock);
        if (child->lli_agl_index == 0) {
                child->lli_agl_index = index;
                spin_unlock(&child->lli_agl_lock);

                LASSERT(list_empty(&child->lli_agl_list));

                igrab(inode);
                spin_lock(&parent->lli_agl_lock);
                if (agl_list_empty(sai))
                        added = 1;
                list_add_tail(&child->lli_agl_list, &sai->sai_entries_agl);
                spin_unlock(&parent->lli_agl_lock);
        } else {
                spin_unlock(&child->lli_agl_lock);
        }

        if (added > 0)
                wake_up(&sai->sai_agl_thread.t_ctl_waitq);
}

static struct ll_statahead_info *ll_sai_alloc(void)
{
        struct ll_statahead_info *sai;
        int                    i;

        sai = kzalloc(sizeof(*sai), GFP_NOFS);
        if (!sai)
                return NULL;

        atomic_set(&sai->sai_refcount, 1);

        spin_lock(&sai_generation_lock);
        sai->sai_generation = ++sai_generation;
        if (unlikely(sai_generation == 0))
                sai->sai_generation = ++sai_generation;
        spin_unlock(&sai_generation_lock);

        sai->sai_max = LL_SA_RPC_MIN;
        sai->sai_index = 1;
        init_waitqueue_head(&sai->sai_waitq);
        init_waitqueue_head(&sai->sai_thread.t_ctl_waitq);
        init_waitqueue_head(&sai->sai_agl_thread.t_ctl_waitq);

        INIT_LIST_HEAD(&sai->sai_entries);
        INIT_LIST_HEAD(&sai->sai_entries_received);
        INIT_LIST_HEAD(&sai->sai_entries_stated);
        INIT_LIST_HEAD(&sai->sai_entries_agl);

        for (i = 0; i < LL_SA_CACHE_SIZE; i++) {
                INIT_LIST_HEAD(&sai->sai_cache[i]);
                spin_lock_init(&sai->sai_cache_lock[i]);
        }
        atomic_set(&sai->sai_cache_count, 0);

        return sai;
}

static inline struct ll_statahead_info *
ll_sai_get(struct ll_statahead_info *sai)
{
        atomic_inc(&sai->sai_refcount);
        return sai;
}

static void ll_sai_put(struct ll_statahead_info *sai)
{
        struct inode     *inode = sai->sai_inode;
        struct ll_inode_info *lli   = ll_i2info(inode);

        if (atomic_dec_and_lock(&sai->sai_refcount, &lli->lli_sa_lock)) {
                struct ll_sa_entry *entry, *next;

                if (unlikely(atomic_read(&sai->sai_refcount) > 0)) {
                        /* It is race case, the interpret callback just hold
                         * a reference count */
                        spin_unlock(&lli->lli_sa_lock);
                        return;
                }

                LASSERT(lli->lli_opendir_key == NULL);
                LASSERT(thread_is_stopped(&sai->sai_thread));
                LASSERT(thread_is_stopped(&sai->sai_agl_thread));

                lli->lli_sai = NULL;
                lli->lli_opendir_pid = 0;
                spin_unlock(&lli->lli_sa_lock);

                if (sai->sai_sent > sai->sai_replied)
                        CDEBUG(D_READA, "statahead for dir "DFID
                              " does not finish: [sent:%llu] [replied:%llu]\n",
                              PFID(&lli->lli_fid),
                              sai->sai_sent, sai->sai_replied);

                list_for_each_entry_safe(entry, next,
                                             &sai->sai_entries, se_link)
                        do_sa_entry_fini(sai, entry);

                LASSERT(list_empty(&sai->sai_entries));
                LASSERT(sa_received_empty(sai));
                LASSERT(list_empty(&sai->sai_entries_stated));

                LASSERT(atomic_read(&sai->sai_cache_count) == 0);
                LASSERT(agl_list_empty(sai));

                iput(inode);
                OBD_FREE_PTR(sai);
        }
}

/* Do NOT forget to drop inode refcount when into sai_entries_agl. */
static void ll_agl_trigger(struct inode *inode, struct ll_statahead_info *sai)
{
        struct ll_inode_info *lli   = ll_i2info(inode);
        __u64            index = lli->lli_agl_index;
        int                rc;

        LASSERT(list_empty(&lli->lli_agl_list));

        /* AGL maybe fall behind statahead with one entry */
        if (is_omitted_entry(sai, index + 1)) {
                lli->lli_agl_index = 0;
                iput(inode);
                return;
        }

        /* Someone is in glimpse (sync or async), do nothing. */
        rc = down_write_trylock(&lli->lli_glimpse_sem);
        if (rc == 0) {
                lli->lli_agl_index = 0;
                iput(inode);
                return;
        }

        /*
         * Someone triggered glimpse within 1 sec before.
         * 1) The former glimpse succeeded with glimpse lock granted by OST, and
         *    if the lock is still cached on client, AGL needs to do nothing. If
         *    it is cancelled by other client, AGL maybe cannot obtain new lock
         *    for no glimpse callback triggered by AGL.
         * 2) The former glimpse succeeded, but OST did not grant glimpse lock.
         *    Under such case, it is quite possible that the OST will not grant
         *    glimpse lock for AGL also.
         * 3) The former glimpse failed, compared with other two cases, it is
         *    relative rare. AGL can ignore such case, and it will not muchly
         *    affect the performance.
         */
        if (lli->lli_glimpse_time != 0 &&
            time_before(cfs_time_shift(-1), lli->lli_glimpse_time)) {
                up_write(&lli->lli_glimpse_sem);
                lli->lli_agl_index = 0;
                iput(inode);
                return;
        }

        CDEBUG(D_READA, "Handling (init) async glimpse: inode = "
               DFID", idx = %llu\n", PFID(&lli->lli_fid), index);

        cl_agl(inode);
        lli->lli_agl_index = 0;
        lli->lli_glimpse_time = cfs_time_current();
        up_write(&lli->lli_glimpse_sem);

        CDEBUG(D_READA, "Handled (init) async glimpse: inode= "
               DFID", idx = %llu, rc = %d\n",
               PFID(&lli->lli_fid), index, rc);

        iput(inode);
}

static void ll_post_statahead(struct ll_statahead_info *sai)
{
        struct inode       *dir   = sai->sai_inode;
        struct inode       *child;
        struct ll_inode_info   *lli   = ll_i2info(dir);
        struct ll_sa_entry     *entry;
        struct md_enqueue_info *minfo;
        struct lookup_intent   *it;
        struct ptlrpc_request  *req;
        struct mdt_body *body;
        int                  rc    = 0;

        spin_lock(&lli->lli_sa_lock);
        if (unlikely(sa_received_empty(sai))) {
                spin_unlock(&lli->lli_sa_lock);
                return;
        }
        entry = sa_first_received_entry(sai);
        atomic_inc(&entry->se_refcount);
        list_del_init(&entry->se_list);
        spin_unlock(&lli->lli_sa_lock);

        LASSERT(entry->se_handle != 0);

        minfo = entry->se_minfo;
        it = &minfo->mi_it;
        req = entry->se_req;
        body = req_capsule_server_get(&req->rq_pill, &RMF_MDT_BODY);
        if (body == NULL) {
                rc = -EFAULT;
                goto out;
        }

        child = entry->se_inode;
        if (child == NULL) {
                /*
                 * lookup.
                 */
                LASSERT(fid_is_zero(&minfo->mi_data.op_fid2));

                /* XXX: No fid in reply, this is probably cross-ref case.
                 * SA can't handle it yet. */
                if (body->valid & OBD_MD_MDS) {
                        rc = -EAGAIN;
                        goto out;
                }
        } else {
                /*
                 * revalidate.
                 */
                /* unlinked and re-created with the same name */
                if (unlikely(!lu_fid_eq(&minfo->mi_data.op_fid2, &body->fid1))){
                        entry->se_inode = NULL;
                        iput(child);
                        child = NULL;
                }
        }

        it->d.lustre.it_lock_handle = entry->se_handle;
        rc = md_revalidate_lock(ll_i2mdexp(dir), it, ll_inode2fid(dir), NULL);
        if (rc != 1) {
                rc = -EAGAIN;
                goto out;
        }

        rc = ll_prep_inode(&child, req, dir->i_sb, it);
        if (rc)
                goto out;

        CDEBUG(D_DLMTRACE, "setting l_data to inode %p (%lu/%u)\n",
               child, child->i_ino, child->i_generation);
        ll_set_lock_data(ll_i2sbi(dir)->ll_md_exp, child, it, NULL);

        entry->se_inode = child;

        if (agl_should_run(sai, child))
                ll_agl_add(sai, child, entry->se_index);

out:
        /* The "ll_sa_entry_to_stated()" will drop related ldlm ibits lock
         * reference count by calling "ll_intent_drop_lock()" in spite of the
         * above operations failed or not. Do not worry about calling
         * "ll_intent_drop_lock()" more than once. */
        rc = ll_sa_entry_to_stated(sai, entry,
                                   rc < 0 ? SA_ENTRY_INVA : SA_ENTRY_SUCC);
        if (rc == 0 && entry->se_index == sai->sai_index_wait)
                wake_up(&sai->sai_waitq);
        ll_sa_entry_put(sai, entry);
}

static int ll_statahead_interpret(struct ptlrpc_request *req,
                                  struct md_enqueue_info *minfo, int rc)
{
        struct lookup_intent     *it  = &minfo->mi_it;
        struct inode         *dir = minfo->mi_dir;
        struct ll_inode_info     *lli = ll_i2info(dir);
        struct ll_statahead_info *sai = NULL;
        struct ll_sa_entry       *entry;
        __u64                     handle = 0;
        int                    wakeup;

        if (it_disposition(it, DISP_LOOKUP_NEG))
                rc = -ENOENT;

        if (rc == 0) {
                /* release ibits lock ASAP to avoid deadlock when statahead
                 * thread enqueues lock on parent in readdir and another
                 * process enqueues lock on child with parent lock held, eg.
                 * unlink. */
                handle = it->d.lustre.it_lock_handle;
                ll_intent_drop_lock(it);
        }

        spin_lock(&lli->lli_sa_lock);
        /* stale entry */
        if (unlikely(lli->lli_sai == NULL ||
                     lli->lli_sai->sai_generation != minfo->mi_generation)) {
                spin_unlock(&lli->lli_sa_lock);
                rc = -ESTALE;
                goto out;
        } else {
                sai = ll_sai_get(lli->lli_sai);
                if (unlikely(!thread_is_running(&sai->sai_thread))) {
                        sai->sai_replied++;
                        spin_unlock(&lli->lli_sa_lock);
                        rc = -EBADFD;
                        goto out;
                }

                entry = ll_sa_entry_get_byindex(sai, minfo->mi_cbdata);
                if (entry == NULL) {
                        sai->sai_replied++;
                        spin_unlock(&lli->lli_sa_lock);
                        rc = -EIDRM;
                        goto out;
                }

                if (rc != 0) {
                        do_sa_entry_to_stated(sai, entry, SA_ENTRY_INVA);
                        wakeup = (entry->se_index == sai->sai_index_wait);
                } else {
                        entry->se_minfo = minfo;
                        entry->se_req = ptlrpc_request_addref(req);
                        /* Release the async ibits lock ASAP to avoid deadlock
                         * when statahead thread tries to enqueue lock on parent
                         * for readpage and other tries to enqueue lock on child
                         * with parent's lock held, for example: unlink. */
                        entry->se_handle = handle;
                        wakeup = sa_received_empty(sai);
                        list_add_tail(&entry->se_list,
                                          &sai->sai_entries_received);
                }
                sai->sai_replied++;
                spin_unlock(&lli->lli_sa_lock);

                ll_sa_entry_put(sai, entry);
                if (wakeup)
                        wake_up(&sai->sai_thread.t_ctl_waitq);
        }

out:
        if (rc != 0) {
                ll_intent_release(it);
                iput(dir);
                OBD_FREE_PTR(minfo);
        }
        if (sai != NULL)
                ll_sai_put(sai);
        return rc;
}

static void sa_args_fini(struct md_enqueue_info *minfo,
                         struct ldlm_enqueue_info *einfo)
{
        LASSERT(minfo && einfo);
        iput(minfo->mi_dir);
        capa_put(minfo->mi_data.op_capa1);
        capa_put(minfo->mi_data.op_capa2);
        OBD_FREE_PTR(minfo);
        OBD_FREE_PTR(einfo);
}

/**
 * There is race condition between "capa_put" and "ll_statahead_interpret" for
 * accessing "op_data.op_capa[1,2]" as following:
 * "capa_put" releases "op_data.op_capa[1,2]"'s reference count after calling
 * "md_intent_getattr_async". But "ll_statahead_interpret" maybe run first, and
 * fill "op_data.op_capa[1,2]" as POISON, then cause "capa_put" access invalid
 * "ocapa". So here reserve "op_data.op_capa[1,2]" in "pcapa" before calling
 * "md_intent_getattr_async".
 */
static int sa_args_init(struct inode *dir, struct inode *child,
                        struct ll_sa_entry *entry, struct md_enqueue_info **pmi,
                        struct ldlm_enqueue_info **pei,
                        struct obd_capa **pcapa)
{
        struct qstr           *qstr = &entry->se_qstr;
        struct ll_inode_info     *lli  = ll_i2info(dir);
        struct md_enqueue_info   *minfo;
        struct ldlm_enqueue_info *einfo;
        struct md_op_data       *op_data;

        einfo = kzalloc(sizeof(*einfo), GFP_NOFS);
        if (!einfo)
                return -ENOMEM;

        minfo = kzalloc(sizeof(*minfo), GFP_NOFS);
        if (!minfo) {
                OBD_FREE_PTR(einfo);
                return -ENOMEM;
        }

        op_data = ll_prep_md_op_data(&minfo->mi_data, dir, child, qstr->name,
                                     qstr->len, 0, LUSTRE_OPC_ANY, NULL);
        if (IS_ERR(op_data)) {
                OBD_FREE_PTR(einfo);
                OBD_FREE_PTR(minfo);
                return PTR_ERR(op_data);
        }

        minfo->mi_it.it_op = IT_GETATTR;
        minfo->mi_dir = igrab(dir);
        minfo->mi_cb = ll_statahead_interpret;
        minfo->mi_generation = lli->lli_sai->sai_generation;
        minfo->mi_cbdata = entry->se_index;

        einfo->ei_type   = LDLM_IBITS;
        einfo->ei_mode   = it_to_lock_mode(&minfo->mi_it);
        einfo->ei_cb_bl  = ll_md_blocking_ast;
        einfo->ei_cb_cp  = ldlm_completion_ast;
        einfo->ei_cb_gl  = NULL;
        einfo->ei_cbdata = NULL;

        *pmi = minfo;
        *pei = einfo;
        pcapa[0] = op_data->op_capa1;
        pcapa[1] = op_data->op_capa2;

        return 0;
}

static int do_sa_lookup(struct inode *dir, struct ll_sa_entry *entry)
{
        struct md_enqueue_info   *minfo;
        struct ldlm_enqueue_info *einfo;
        struct obd_capa   *capas[2];
        int                    rc;

        rc = sa_args_init(dir, NULL, entry, &minfo, &einfo, capas);
        if (rc)
                return rc;

        rc = md_intent_getattr_async(ll_i2mdexp(dir), minfo, einfo);
        if (!rc) {
                capa_put(capas[0]);
                capa_put(capas[1]);
        } else {
                sa_args_fini(minfo, einfo);
        }

        return rc;
}

/**
 * similar to ll_revalidate_it().
 * \retval      1 -- dentry valid
 * \retval      0 -- will send stat-ahead request
 * \retval others -- prepare stat-ahead request failed
 */
static int do_sa_revalidate(struct inode *dir, struct ll_sa_entry *entry,
                            struct dentry *dentry)
{
        struct inode         *inode = d_inode(dentry);
        struct lookup_intent      it = { .it_op = IT_GETATTR,
                                         .d.lustre.it_lock_handle = 0 };
        struct md_enqueue_info   *minfo;
        struct ldlm_enqueue_info *einfo;
        struct obd_capa   *capas[2];
        int rc;

        if (unlikely(inode == NULL))
                return 1;

        if (d_mountpoint(dentry))
                return 1;

        entry->se_inode = igrab(inode);
        rc = md_revalidate_lock(ll_i2mdexp(dir), &it, ll_inode2fid(inode),
                                NULL);
        if (rc == 1) {
                entry->se_handle = it.d.lustre.it_lock_handle;
                ll_intent_release(&it);
                return 1;
        }

        rc = sa_args_init(dir, inode, entry, &minfo, &einfo, capas);
        if (rc) {
                entry->se_inode = NULL;
                iput(inode);
                return rc;
        }

        rc = md_intent_getattr_async(ll_i2mdexp(dir), minfo, einfo);
        if (!rc) {
                capa_put(capas[0]);
                capa_put(capas[1]);
        } else {
                entry->se_inode = NULL;
                iput(inode);
                sa_args_fini(minfo, einfo);
        }

        return rc;
}

static void ll_statahead_one(struct dentry *parent, const char *entry_name,
                             int entry_name_len)
{
        struct inode         *dir    = d_inode(parent);
        struct ll_inode_info     *lli    = ll_i2info(dir);
        struct ll_statahead_info *sai    = lli->lli_sai;
        struct dentry       *dentry = NULL;
        struct ll_sa_entry       *entry;
        int                    rc;
        int                    rc1;

        entry = ll_sa_entry_alloc(sai, sai->sai_index, entry_name,
                                  entry_name_len);
        if (IS_ERR(entry))
                return;

        dentry = d_lookup(parent, &entry->se_qstr);
        if (!dentry) {
                rc = do_sa_lookup(dir, entry);
        } else {
                rc = do_sa_revalidate(dir, entry, dentry);
                if (rc == 1 && agl_should_run(sai, d_inode(dentry)))
                        ll_agl_add(sai, d_inode(dentry), entry->se_index);
        }

        if (dentry != NULL)
                dput(dentry);

        if (rc) {
                rc1 = ll_sa_entry_to_stated(sai, entry,
                                        rc < 0 ? SA_ENTRY_INVA : SA_ENTRY_SUCC);
                if (rc1 == 0 && entry->se_index == sai->sai_index_wait)
                        wake_up(&sai->sai_waitq);
        } else {
                sai->sai_sent++;
        }

        sai->sai_index++;
        /* drop one refcount on entry by ll_sa_entry_alloc */
        ll_sa_entry_put(sai, entry);
}

static int ll_agl_thread(void *arg)
{
        struct dentry       *parent = (struct dentry *)arg;
        struct inode         *dir    = d_inode(parent);
        struct ll_inode_info     *plli   = ll_i2info(dir);
        struct ll_inode_info     *clli;
        struct ll_sb_info       *sbi    = ll_i2sbi(dir);
        struct ll_statahead_info *sai    = ll_sai_get(plli->lli_sai);
        struct ptlrpc_thread     *thread = &sai->sai_agl_thread;
        struct l_wait_info      lwi    = { 0 };

        thread->t_pid = current_pid();
        CDEBUG(D_READA, "agl thread started: sai %p, parent %pd\n",
               sai, parent);

        atomic_inc(&sbi->ll_agl_total);
        spin_lock(&plli->lli_agl_lock);
        sai->sai_agl_valid = 1;
        if (thread_is_init(thread))
                /* If someone else has changed the thread state
                 * (e.g. already changed to SVC_STOPPING), we can't just
                 * blindly overwrite that setting. */
                thread_set_flags(thread, SVC_RUNNING);
        spin_unlock(&plli->lli_agl_lock);
        wake_up(&thread->t_ctl_waitq);

        while (1) {
                l_wait_event(thread->t_ctl_waitq,
                             !agl_list_empty(sai) ||
                             !thread_is_running(thread),
                             &lwi);

                if (!thread_is_running(thread))
                        break;

                spin_lock(&plli->lli_agl_lock);
                /* The statahead thread maybe help to process AGL entries,
                 * so check whether list empty again. */
                if (!agl_list_empty(sai)) {
                        clli = agl_first_entry(sai);
                        list_del_init(&clli->lli_agl_list);
                        spin_unlock(&plli->lli_agl_lock);
                        ll_agl_trigger(&clli->lli_vfs_inode, sai);
                } else {
                        spin_unlock(&plli->lli_agl_lock);
                }
        }

        spin_lock(&plli->lli_agl_lock);
        sai->sai_agl_valid = 0;
        while (!agl_list_empty(sai)) {
                clli = agl_first_entry(sai);
                list_del_init(&clli->lli_agl_list);
                spin_unlock(&plli->lli_agl_lock);
                clli->lli_agl_index = 0;
                iput(&clli->lli_vfs_inode);
                spin_lock(&plli->lli_agl_lock);
        }
        thread_set_flags(thread, SVC_STOPPED);
        spin_unlock(&plli->lli_agl_lock);
        wake_up(&thread->t_ctl_waitq);
        ll_sai_put(sai);
        CDEBUG(D_READA, "agl thread stopped: sai %p, parent %pd\n",
               sai, parent);
        return 0;
}

static void ll_start_agl(struct dentry *parent, struct ll_statahead_info *sai)
{
        struct ptlrpc_thread *thread = &sai->sai_agl_thread;
        struct l_wait_info    lwi    = { 0 };
        struct ll_inode_info  *plli;
        struct task_struct *task;

        CDEBUG(D_READA, "start agl thread: sai %p, parent %pd\n",
               sai, parent);

        plli = ll_i2info(d_inode(parent));
        task = kthread_run(ll_agl_thread, parent,
                               "ll_agl_%u", plli->lli_opendir_pid);
        if (IS_ERR(task)) {
                CERROR("can't start ll_agl thread, rc: %ld\n", PTR_ERR(task));
                thread_set_flags(thread, SVC_STOPPED);
                return;
        }

        l_wait_event(thread->t_ctl_waitq,
                     thread_is_running(thread) || thread_is_stopped(thread),
                     &lwi);
}

static int ll_statahead_thread(void *arg)
{
        struct dentry       *parent = (struct dentry *)arg;
        struct inode         *dir    = d_inode(parent);
        struct ll_inode_info     *plli   = ll_i2info(dir);
        struct ll_inode_info     *clli;
        struct ll_sb_info       *sbi    = ll_i2sbi(dir);
        struct ll_statahead_info *sai    = ll_sai_get(plli->lli_sai);
        struct ptlrpc_thread     *thread = &sai->sai_thread;
        struct ptlrpc_thread *agl_thread = &sai->sai_agl_thread;
        struct page           *page;
        __u64                pos    = 0;
        int                    first  = 0;
        int                    rc     = 0;
        struct ll_dir_chain       chain;
        struct l_wait_info      lwi    = { 0 };

        thread->t_pid = current_pid();
        CDEBUG(D_READA, "statahead thread starting: sai %p, parent %pd\n",
               sai, parent);

        if (sbi->ll_flags & LL_SBI_AGL_ENABLED)
                ll_start_agl(parent, sai);

        atomic_inc(&sbi->ll_sa_total);
        spin_lock(&plli->lli_sa_lock);
        if (thread_is_init(thread))
                /* If someone else has changed the thread state
                 * (e.g. already changed to SVC_STOPPING), we can't just
                 * blindly overwrite that setting. */
                thread_set_flags(thread, SVC_RUNNING);
        spin_unlock(&plli->lli_sa_lock);
        wake_up(&thread->t_ctl_waitq);

        ll_dir_chain_init(&chain);
        page = ll_get_dir_page(dir, pos, &chain);

        while (1) {
                struct lu_dirpage *dp;
                struct lu_dirent  *ent;

                if (IS_ERR(page)) {
                        rc = PTR_ERR(page);
                        CDEBUG(D_READA, "error reading dir "DFID" at %llu/%llu: [rc %d] [parent %u]\n",
                               PFID(ll_inode2fid(dir)), pos, sai->sai_index,
                               rc, plli->lli_opendir_pid);
                        goto out;
                }

                dp = page_address(page);
                for (ent = lu_dirent_start(dp); ent != NULL;
                     ent = lu_dirent_next(ent)) {
                        __u64 hash;
                        int namelen;
                        char *name;

                        hash = le64_to_cpu(ent->lde_hash);
                        if (unlikely(hash < pos))
                                /*
                                 * Skip until we find target hash value.
                                 */
                                continue;

                        namelen = le16_to_cpu(ent->lde_namelen);
                        if (unlikely(namelen == 0))
                                /*
                                 * Skip dummy record.
                                 */
                                continue;

                        name = ent->lde_name;
                        if (name[0] == '.') {
                                if (namelen == 1) {
                                        /*
                                         * skip "."
                                         */
                                        continue;
                                } else if (name[1] == '.' && namelen == 2) {
                                        /*
                                         * skip ".."
                                         */
                                        continue;
                                } else if (!sai->sai_ls_all) {
                                        /*
                                         * skip hidden files.
                                         */
                                        sai->sai_skip_hidden++;
                                        continue;
                                }
                        }

                        /*
                         * don't stat-ahead first entry.
                         */
                        if (unlikely(++first == 1))
                                continue;

keep_it:
                        l_wait_event(thread->t_ctl_waitq,
                                     !sa_sent_full(sai) ||
                                     !sa_received_empty(sai) ||
                                     !agl_list_empty(sai) ||
                                     !thread_is_running(thread),
                                     &lwi);

interpret_it:
                        while (!sa_received_empty(sai))
                                ll_post_statahead(sai);

                        if (unlikely(!thread_is_running(thread))) {
                                ll_release_page(page, 0);
                                rc = 0;
                                goto out;
                        }

                        /* If no window for metadata statahead, but there are
                         * some AGL entries to be triggered, then try to help
                         * to process the AGL entries. */
                        if (sa_sent_full(sai)) {
                                spin_lock(&plli->lli_agl_lock);
                                while (!agl_list_empty(sai)) {
                                        clli = agl_first_entry(sai);
                                        list_del_init(&clli->lli_agl_list);
                                        spin_unlock(&plli->lli_agl_lock);
                                        ll_agl_trigger(&clli->lli_vfs_inode,
                                                       sai);

                                        if (!sa_received_empty(sai))
                                                goto interpret_it;

                                        if (unlikely(
                                                !thread_is_running(thread))) {
                                                ll_release_page(page, 0);
                                                rc = 0;
                                                goto out;
                                        }

                                        if (!sa_sent_full(sai))
                                                goto do_it;

                                        spin_lock(&plli->lli_agl_lock);
                                }
                                spin_unlock(&plli->lli_agl_lock);

                                goto keep_it;
                        }

do_it:
                        ll_statahead_one(parent, name, namelen);
                }
                pos = le64_to_cpu(dp->ldp_hash_end);
                if (pos == MDS_DIR_END_OFF) {
                        /*
                         * End of directory reached.
                         */
                        ll_release_page(page, 0);
                        while (1) {
                                l_wait_event(thread->t_ctl_waitq,
                                             !sa_received_empty(sai) ||
                                             sai->sai_sent == sai->sai_replied||
                                             !thread_is_running(thread),
                                             &lwi);

                                while (!sa_received_empty(sai))
                                        ll_post_statahead(sai);

                                if (unlikely(!thread_is_running(thread))) {
                                        rc = 0;
                                        goto out;
                                }

                                if (sai->sai_sent == sai->sai_replied &&
                                    sa_received_empty(sai))
                                        break;
                        }

                        spin_lock(&plli->lli_agl_lock);
                        while (!agl_list_empty(sai) &&
                               thread_is_running(thread)) {
                                clli = agl_first_entry(sai);
                                list_del_init(&clli->lli_agl_list);
                                spin_unlock(&plli->lli_agl_lock);
                                ll_agl_trigger(&clli->lli_vfs_inode, sai);
                                spin_lock(&plli->lli_agl_lock);
                        }
                        spin_unlock(&plli->lli_agl_lock);

                        rc = 0;
                        goto out;
                } else if (1) {
                        /*
                         * chain is exhausted.
                         * Normal case: continue to the next page.
                         */
                        ll_release_page(page, le32_to_cpu(dp->ldp_flags) &
                                              LDF_COLLIDE);
                        page = ll_get_dir_page(dir, pos, &chain);
                } else {
                        LASSERT(le32_to_cpu(dp->ldp_flags) & LDF_COLLIDE);
                        ll_release_page(page, 1);
                        /*
                         * go into overflow page.
                         */
                }
        }

out:
        if (sai->sai_agl_valid) {
                spin_lock(&plli->lli_agl_lock);
                thread_set_flags(agl_thread, SVC_STOPPING);
                spin_unlock(&plli->lli_agl_lock);
                wake_up(&agl_thread->t_ctl_waitq);

                CDEBUG(D_READA, "stop agl thread: sai %p pid %u\n",
                       sai, (unsigned int)agl_thread->t_pid);
                l_wait_event(agl_thread->t_ctl_waitq,
                             thread_is_stopped(agl_thread),
                             &lwi);
        } else {
                /* Set agl_thread flags anyway. */
                thread_set_flags(&sai->sai_agl_thread, SVC_STOPPED);
        }
        ll_dir_chain_fini(&chain);
        spin_lock(&plli->lli_sa_lock);
        if (!sa_received_empty(sai)) {
                thread_set_flags(thread, SVC_STOPPING);
                spin_unlock(&plli->lli_sa_lock);

                /* To release the resources held by received entries. */
                while (!sa_received_empty(sai))
                        ll_post_statahead(sai);

                spin_lock(&plli->lli_sa_lock);
        }
        thread_set_flags(thread, SVC_STOPPED);
        spin_unlock(&plli->lli_sa_lock);
        wake_up(&sai->sai_waitq);
        wake_up(&thread->t_ctl_waitq);
        ll_sai_put(sai);
        dput(parent);
        CDEBUG(D_READA, "statahead thread stopped: sai %p, parent %pd\n",
               sai, parent);
        return rc;
}

/**
 * called in ll_file_release().
 */
void ll_stop_statahead(struct inode *dir, void *key)
{
        struct ll_inode_info *lli = ll_i2info(dir);

        if (unlikely(key == NULL))
                return;

        spin_lock(&lli->lli_sa_lock);
        if (lli->lli_opendir_key != key || lli->lli_opendir_pid == 0) {
                spin_unlock(&lli->lli_sa_lock);
                return;
        }

        lli->lli_opendir_key = NULL;

        if (lli->lli_sai) {
                struct l_wait_info lwi = { 0 };
                struct ptlrpc_thread *thread = &lli->lli_sai->sai_thread;

                if (!thread_is_stopped(thread)) {
                        thread_set_flags(thread, SVC_STOPPING);
                        spin_unlock(&lli->lli_sa_lock);
                        wake_up(&thread->t_ctl_waitq);

                        CDEBUG(D_READA, "stop statahead thread: sai %p pid %u\n",
                               lli->lli_sai, (unsigned int)thread->t_pid);
                        l_wait_event(thread->t_ctl_waitq,
                                     thread_is_stopped(thread),
                                     &lwi);
                } else {
                        spin_unlock(&lli->lli_sa_lock);
                }

                /*
                 * Put the ref which was held when first statahead_enter.
                 * It maybe not the last ref for some statahead requests
                 * maybe inflight.
                 */
                ll_sai_put(lli->lli_sai);
        } else {
                lli->lli_opendir_pid = 0;
                spin_unlock(&lli->lli_sa_lock);
        }
}

enum {
        /**
         * not first dirent, or is "."
         */
        LS_NONE_FIRST_DE = 0,
        /**
         * the first non-hidden dirent
         */
        LS_FIRST_DE,
        /**
         * the first hidden dirent, that is "."
         */
        LS_FIRST_DOT_DE
};

static int is_first_dirent(struct inode *dir, struct dentry *dentry)
{
        struct ll_dir_chain   chain;
        struct qstr       *target = &dentry->d_name;
        struct page       *page;
        __u64            pos    = 0;
        int                dot_de;
        int                rc     = LS_NONE_FIRST_DE;

        ll_dir_chain_init(&chain);
        page = ll_get_dir_page(dir, pos, &chain);

        while (1) {
                struct lu_dirpage *dp;
                struct lu_dirent  *ent;

                if (IS_ERR(page)) {
                        struct ll_inode_info *lli = ll_i2info(dir);

                        rc = PTR_ERR(page);
                        CERROR("error reading dir "DFID" at %llu: [rc %d] [parent %u]\n",
                               PFID(ll_inode2fid(dir)), pos,
                               rc, lli->lli_opendir_pid);
                        break;
                }

                dp = page_address(page);
                for (ent = lu_dirent_start(dp); ent != NULL;
                     ent = lu_dirent_next(ent)) {
                        __u64 hash;
                        int namelen;
                        char *name;

                        hash = le64_to_cpu(ent->lde_hash);
                        /* The ll_get_dir_page() can return any page containing
                         * the given hash which may be not the start hash. */
                        if (unlikely(hash < pos))
                                continue;

                        namelen = le16_to_cpu(ent->lde_namelen);
                        if (unlikely(namelen == 0))
                                /*
                                 * skip dummy record.
                                 */
                                continue;

                        name = ent->lde_name;
                        if (name[0] == '.') {
                                if (namelen == 1)
                                        /*
                                         * skip "."
                                         */
                                        continue;
                                else if (name[1] == '.' && namelen == 2)
                                        /*
                                         * skip ".."
                                         */
                                        continue;
                                else
                                        dot_de = 1;
                        } else {
                                dot_de = 0;
                        }

                        if (dot_de && target->name[0] != '.') {
                                CDEBUG(D_READA, "%.*s skip hidden file %.*s\n",
                                       target->len, target->name,
                                       namelen, name);
                                continue;
                        }

                        if (target->len != namelen ||
                            memcmp(target->name, name, namelen) != 0)
                                rc = LS_NONE_FIRST_DE;
                        else if (!dot_de)
                                rc = LS_FIRST_DE;
                        else
                                rc = LS_FIRST_DOT_DE;

                        ll_release_page(page, 0);
                        goto out;
                }
                pos = le64_to_cpu(dp->ldp_hash_end);
                if (pos == MDS_DIR_END_OFF) {
                        /*
                         * End of directory reached.
                         */
                        ll_release_page(page, 0);
                        break;
                } else if (1) {
                        /*
                         * chain is exhausted
                         * Normal case: continue to the next page.
                         */
                        ll_release_page(page, le32_to_cpu(dp->ldp_flags) &
                                              LDF_COLLIDE);
                        page = ll_get_dir_page(dir, pos, &chain);
                } else {
                        /*
                         * go into overflow page.
                         */
                        LASSERT(le32_to_cpu(dp->ldp_flags) & LDF_COLLIDE);
                        ll_release_page(page, 1);
                }
        }

out:
        ll_dir_chain_fini(&chain);
        return rc;
}

static void
ll_sai_unplug(struct ll_statahead_info *sai, struct ll_sa_entry *entry)
{
        struct ptlrpc_thread *thread = &sai->sai_thread;
        struct ll_sb_info    *sbi    = ll_i2sbi(sai->sai_inode);
        int                hit;

        if (entry != NULL && entry->se_stat == SA_ENTRY_SUCC)
                hit = 1;
        else
                hit = 0;

        ll_sa_entry_fini(sai, entry);
        if (hit) {
                sai->sai_hit++;
                sai->sai_consecutive_miss = 0;
                sai->sai_max = min(2 * sai->sai_max, sbi->ll_sa_max);
        } else {
                struct ll_inode_info *lli = ll_i2info(sai->sai_inode);

                sai->sai_miss++;
                sai->sai_consecutive_miss++;
                if (sa_low_hit(sai) && thread_is_running(thread)) {
                        atomic_inc(&sbi->ll_sa_wrong);
                        CDEBUG(D_READA, "Statahead for dir " DFID " hit ratio too low: hit/miss %llu/%llu, sent/replied %llu/%llu, stopping statahead thread\n",
                               PFID(&lli->lli_fid), sai->sai_hit,
                               sai->sai_miss, sai->sai_sent,
                               sai->sai_replied);
                        spin_lock(&lli->lli_sa_lock);
                        if (!thread_is_stopped(thread))
                                thread_set_flags(thread, SVC_STOPPING);
                        spin_unlock(&lli->lli_sa_lock);
                }
        }

        if (!thread_is_stopped(thread))
                wake_up(&thread->t_ctl_waitq);
}

/**
 * Start statahead thread if this is the first dir entry.
 * Otherwise if a thread is started already, wait it until it is ahead of me.
 * \retval 1       -- find entry with lock in cache, the caller needs to do
 *                  nothing.
 * \retval 0       -- find entry in cache, but without lock, the caller needs
 *                  refresh from MDS.
 * \retval others  -- the caller need to process as non-statahead.
 */
int do_statahead_enter(struct inode *dir, struct dentry **dentryp,
                       int only_unplug)
{
        struct ll_inode_info     *lli   = ll_i2info(dir);
        struct ll_statahead_info *sai   = lli->lli_sai;
        struct dentry       *parent;
        struct ll_sa_entry       *entry;
        struct ptlrpc_thread     *thread;
        struct l_wait_info      lwi   = { 0 };
        int                    rc    = 0;
        struct ll_inode_info     *plli;

        LASSERT(lli->lli_opendir_pid == current_pid());

        if (sai) {
                thread = &sai->sai_thread;
                if (unlikely(thread_is_stopped(thread) &&
                             list_empty(&sai->sai_entries_stated))) {
                        /* to release resource */
                        ll_stop_statahead(dir, lli->lli_opendir_key);
                        return -EAGAIN;
                }

                if ((*dentryp)->d_name.name[0] == '.') {
                        if (sai->sai_ls_all ||
                            sai->sai_miss_hidden >= sai->sai_skip_hidden) {
                                /*
                                 * Hidden dentry is the first one, or statahead
                                 * thread does not skip so many hidden dentries
                                 * before "sai_ls_all" enabled as below.
                                 */
                        } else {
                                if (!sai->sai_ls_all)
                                        /*
                                         * It maybe because hidden dentry is not
                                         * the first one, "sai_ls_all" was not
                                         * set, then "ls -al" missed. Enable
                                         * "sai_ls_all" for such case.
                                         */
                                        sai->sai_ls_all = 1;

                                /*
                                 * Such "getattr" has been skipped before
                                 * "sai_ls_all" enabled as above.
                                 */
                                sai->sai_miss_hidden++;
                                return -EAGAIN;
                        }
                }

                entry = ll_sa_entry_get_byname(sai, &(*dentryp)->d_name);
                if (entry == NULL || only_unplug) {
                        ll_sai_unplug(sai, entry);
                        return entry ? 1 : -EAGAIN;
                }

                if (!ll_sa_entry_stated(entry)) {
                        sai->sai_index_wait = entry->se_index;
                        lwi = LWI_TIMEOUT_INTR(cfs_time_seconds(30), NULL,
                                               LWI_ON_SIGNAL_NOOP, NULL);
                        rc = l_wait_event(sai->sai_waitq,
                                          ll_sa_entry_stated(entry) ||
                                          thread_is_stopped(thread),
                                          &lwi);
                        if (rc < 0) {
                                ll_sai_unplug(sai, entry);
                                return -EAGAIN;
                        }
                }

                if (entry->se_stat == SA_ENTRY_SUCC &&
                    entry->se_inode != NULL) {
                        struct inode *inode = entry->se_inode;
                        struct lookup_intent it = { .it_op = IT_GETATTR,
                                                    .d.lustre.it_lock_handle =
                                                     entry->se_handle };
                        __u64 bits;

                        rc = md_revalidate_lock(ll_i2mdexp(dir), &it,
                                                ll_inode2fid(inode), &bits);
                        if (rc == 1) {
                                if (d_inode(*dentryp) == NULL) {
                                        struct dentry *alias;

                                        alias = ll_splice_alias(inode,
                                                                   *dentryp);
                                        if (IS_ERR(alias)) {
                                                ll_sai_unplug(sai, entry);
                                                return PTR_ERR(alias);
                                        }
                                        *dentryp = alias;
                                } else if (d_inode(*dentryp) != inode) {
                                        /* revalidate, but inode is recreated */
                                        CDEBUG(D_READA,
                                              "stale dentry %pd inode %lu/%u, statahead inode %lu/%u\n",
                                              *dentryp,
                                              d_inode(*dentryp)->i_ino,
                                              d_inode(*dentryp)->i_generation,
                                              inode->i_ino,
                                              inode->i_generation);
                                        ll_sai_unplug(sai, entry);
                                        return -ESTALE;
                                } else {
                                        iput(inode);
                                }
                                entry->se_inode = NULL;

                                if ((bits & MDS_INODELOCK_LOOKUP) &&
                                    d_lustre_invalid(*dentryp))
                                        d_lustre_revalidate(*dentryp);
                                ll_intent_release(&it);
                        }
                }

                ll_sai_unplug(sai, entry);
                return rc;
        }

        /* I am the "lli_opendir_pid" owner, only me can set "lli_sai". */
        rc = is_first_dirent(dir, *dentryp);
        if (rc == LS_NONE_FIRST_DE) {
                /* It is not "ls -{a}l" operation, no need statahead for it. */
                rc = -EAGAIN;
                goto out;
        }

        sai = ll_sai_alloc();
        if (sai == NULL) {
                rc = -ENOMEM;
                goto out;
        }

        sai->sai_ls_all = (rc == LS_FIRST_DOT_DE);
        sai->sai_inode = igrab(dir);
        if (unlikely(sai->sai_inode == NULL)) {
                CWARN("Do not start stat ahead on dying inode "DFID"\n",
                      PFID(&lli->lli_fid));
                rc = -ESTALE;
                goto out;
        }

        /* get parent reference count here, and put it in ll_statahead_thread */
        parent = dget((*dentryp)->d_parent);
        if (unlikely(sai->sai_inode != d_inode(parent))) {
                struct ll_inode_info *nlli = ll_i2info(d_inode(parent));

                CWARN("Race condition, someone changed %pd just now: old parent "DFID", new parent "DFID"\n",
                      *dentryp,
                      PFID(&lli->lli_fid), PFID(&nlli->lli_fid));
                dput(parent);
                iput(sai->sai_inode);
                rc = -EAGAIN;
                goto out;
        }

        CDEBUG(D_READA, "start statahead thread: sai %p, parent %pd\n",
               sai, parent);

        /* The sai buffer already has one reference taken at allocation time,
         * but as soon as we expose the sai by attaching it to the lli that
         * default reference can be dropped by another thread calling
         * ll_stop_statahead. We need to take a local reference to protect
         * the sai buffer while we intend to access it. */
        ll_sai_get(sai);
        lli->lli_sai = sai;

        plli = ll_i2info(d_inode(parent));
        rc = PTR_ERR(kthread_run(ll_statahead_thread, parent,
                                 "ll_sa_%u", plli->lli_opendir_pid));
        thread = &sai->sai_thread;
        if (IS_ERR_VALUE(rc)) {
                CERROR("can't start ll_sa thread, rc: %d\n", rc);
                dput(parent);
                lli->lli_opendir_key = NULL;
                thread_set_flags(thread, SVC_STOPPED);
                thread_set_flags(&sai->sai_agl_thread, SVC_STOPPED);
                /* Drop both our own local reference and the default
                 * reference from allocation time. */
                ll_sai_put(sai);
                ll_sai_put(sai);
                LASSERT(lli->lli_sai == NULL);
                return -EAGAIN;
        }

        l_wait_event(thread->t_ctl_waitq,
                     thread_is_running(thread) || thread_is_stopped(thread),
                     &lwi);
        ll_sai_put(sai);

        /*
         * We don't stat-ahead for the first dirent since we are already in
         * lookup.
         */
        return -EAGAIN;

out:
        if (sai != NULL)
                OBD_FREE_PTR(sai);
        spin_lock(&lli->lli_sa_lock);
        lli->lli_opendir_key = NULL;
        lli->lli_opendir_pid = 0;
        spin_unlock(&lli->lli_sa_lock);
        return rc;
}