Merge branch 'v6v7' into devel

[linux/fpc-iii.git] / fs / gfs2 / glock.c

/*
 * Copyright (C) Sistina Software, Inc.  1997-2003 All rights reserved.
 * Copyright (C) 2004-2008 Red Hat, Inc.  All rights reserved.
 *
 * This copyrighted material is made available to anyone wishing to use,
 * modify, copy, or redistribute it subject to the terms and conditions
 * of the GNU General Public License version 2.
 */

#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/buffer_head.h>
#include <linux/delay.h>
#include <linux/sort.h>
#include <linux/jhash.h>
#include <linux/kallsyms.h>
#include <linux/gfs2_ondisk.h>
#include <linux/list.h>
#include <linux/wait.h>
#include <linux/module.h>
#include <asm/uaccess.h>
#include <linux/seq_file.h>
#include <linux/debugfs.h>
#include <linux/kthread.h>
#include <linux/freezer.h>
#include <linux/workqueue.h>
#include <linux/jiffies.h>

#include "gfs2.h"
#include "incore.h"
#include "glock.h"
#include "glops.h"
#include "inode.h"
#include "lops.h"
#include "meta_io.h"
#include "quota.h"
#include "super.h"
#include "util.h"
#include "bmap.h"
#define CREATE_TRACE_POINTS
#include "trace_gfs2.h"

struct gfs2_gl_hash_bucket {
        struct hlist_head hb_list;
};

struct gfs2_glock_iter {
        int hash;                       /* hash bucket index         */
        struct gfs2_sbd *sdp;           /* incore superblock         */
        struct gfs2_glock *gl;          /* current glock struct      */
        char string[512];               /* scratch space             */
};

typedef void (*glock_examiner) (struct gfs2_glock * gl);

static int gfs2_dump_lockstate(struct gfs2_sbd *sdp);
static int __dump_glock(struct seq_file *seq, const struct gfs2_glock *gl);
#define GLOCK_BUG_ON(gl,x) do { if (unlikely(x)) { __dump_glock(NULL, gl); BUG(); } } while(0)
static void do_xmote(struct gfs2_glock *gl, struct gfs2_holder *gh, unsigned int target);

static struct dentry *gfs2_root;
static struct workqueue_struct *glock_workqueue;
struct workqueue_struct *gfs2_delete_workqueue;
static LIST_HEAD(lru_list);
static atomic_t lru_count = ATOMIC_INIT(0);
static DEFINE_SPINLOCK(lru_lock);

#define GFS2_GL_HASH_SHIFT      15
#define GFS2_GL_HASH_SIZE       (1 << GFS2_GL_HASH_SHIFT)
#define GFS2_GL_HASH_MASK       (GFS2_GL_HASH_SIZE - 1)

static struct gfs2_gl_hash_bucket gl_hash_table[GFS2_GL_HASH_SIZE];
static struct dentry *gfs2_root;

/*
 * Despite what you might think, the numbers below are not arbitrary :-)
 * They are taken from the ipv4 routing hash code, which is well tested
 * and thus should be nearly optimal. Later on we might tweek the numbers
 * but for now this should be fine.
 *
 * The reason for putting the locks in a separate array from the list heads
 * is that we can have fewer locks than list heads and save memory. We use
 * the same hash function for both, but with a different hash mask.
 */
#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK) || \
        defined(CONFIG_PROVE_LOCKING)

#ifdef CONFIG_LOCKDEP
# define GL_HASH_LOCK_SZ        256
#else
# if NR_CPUS >= 32
#  define GL_HASH_LOCK_SZ       4096
# elif NR_CPUS >= 16
#  define GL_HASH_LOCK_SZ       2048
# elif NR_CPUS >= 8
#  define GL_HASH_LOCK_SZ       1024
# elif NR_CPUS >= 4
#  define GL_HASH_LOCK_SZ       512
# else
#  define GL_HASH_LOCK_SZ       256
# endif
#endif

/* We never want more locks than chains */
#if GFS2_GL_HASH_SIZE < GL_HASH_LOCK_SZ
# undef GL_HASH_LOCK_SZ
# define GL_HASH_LOCK_SZ GFS2_GL_HASH_SIZE
#endif

static rwlock_t gl_hash_locks[GL_HASH_LOCK_SZ];

static inline rwlock_t *gl_lock_addr(unsigned int x)
{
        return &gl_hash_locks[x & (GL_HASH_LOCK_SZ-1)];
}
#else /* not SMP, so no spinlocks required */
static inline rwlock_t *gl_lock_addr(unsigned int x)
{
        return NULL;
}
#endif

/**
 * gl_hash() - Turn glock number into hash bucket number
 * @lock: The glock number
 *
 * Returns: The number of the corresponding hash bucket
 */

static unsigned int gl_hash(const struct gfs2_sbd *sdp,
                            const struct lm_lockname *name)
{
        unsigned int h;

        h = jhash(&name->ln_number, sizeof(u64), 0);
        h = jhash(&name->ln_type, sizeof(unsigned int), h);
        h = jhash(&sdp, sizeof(struct gfs2_sbd *), h);
        h &= GFS2_GL_HASH_MASK;

        return h;
}

/**
 * glock_free() - Perform a few checks and then release struct gfs2_glock
 * @gl: The glock to release
 *
 * Also calls lock module to release its internal structure for this glock.
 *
 */

static void glock_free(struct gfs2_glock *gl)
{
        struct gfs2_sbd *sdp = gl->gl_sbd;
        struct address_space *mapping = gfs2_glock2aspace(gl);
        struct kmem_cache *cachep = gfs2_glock_cachep;

        GLOCK_BUG_ON(gl, mapping && mapping->nrpages);
        trace_gfs2_glock_put(gl);
        if (mapping)
                cachep = gfs2_glock_aspace_cachep;
        sdp->sd_lockstruct.ls_ops->lm_put_lock(cachep, gl);
}

/**
 * gfs2_glock_hold() - increment reference count on glock
 * @gl: The glock to hold
 *
 */

void gfs2_glock_hold(struct gfs2_glock *gl)
{
        GLOCK_BUG_ON(gl, atomic_read(&gl->gl_ref) == 0);
        atomic_inc(&gl->gl_ref);
}

/**
 * demote_ok - Check to see if it's ok to unlock a glock
 * @gl: the glock
 *
 * Returns: 1 if it's ok
 */

static int demote_ok(const struct gfs2_glock *gl)
{
        const struct gfs2_glock_operations *glops = gl->gl_ops;

        if (gl->gl_state == LM_ST_UNLOCKED)
                return 0;
        if (!list_empty(&gl->gl_holders))
                return 0;
        if (glops->go_demote_ok)
                return glops->go_demote_ok(gl);
        return 1;
}

/**
 * gfs2_glock_schedule_for_reclaim - Add a glock to the reclaim list
 * @gl: the glock
 *
 */

static void gfs2_glock_schedule_for_reclaim(struct gfs2_glock *gl)
{
        int may_reclaim;
        may_reclaim = (demote_ok(gl) &&
                       (atomic_read(&gl->gl_ref) == 1 ||
                        (gl->gl_name.ln_type == LM_TYPE_INODE &&
                         atomic_read(&gl->gl_ref) <= 2)));
        spin_lock(&lru_lock);
        if (list_empty(&gl->gl_lru) && may_reclaim) {
                list_add_tail(&gl->gl_lru, &lru_list);
                atomic_inc(&lru_count);
        }
        spin_unlock(&lru_lock);
}

/**
 * gfs2_glock_put_nolock() - Decrement reference count on glock
 * @gl: The glock to put
 *
 * This function should only be used if the caller has its own reference
 * to the glock, in addition to the one it is dropping.
 */

void gfs2_glock_put_nolock(struct gfs2_glock *gl)
{
        if (atomic_dec_and_test(&gl->gl_ref))
                GLOCK_BUG_ON(gl, 1);
        gfs2_glock_schedule_for_reclaim(gl);
}

/**
 * gfs2_glock_put() - Decrement reference count on glock
 * @gl: The glock to put
 *
 */

int gfs2_glock_put(struct gfs2_glock *gl)
{
        int rv = 0;

        write_lock(gl_lock_addr(gl->gl_hash));
        if (atomic_dec_and_lock(&gl->gl_ref, &lru_lock)) {
                hlist_del(&gl->gl_list);
                if (!list_empty(&gl->gl_lru)) {
                        list_del_init(&gl->gl_lru);
                        atomic_dec(&lru_count);
                }
                spin_unlock(&lru_lock);
                write_unlock(gl_lock_addr(gl->gl_hash));
                GLOCK_BUG_ON(gl, !list_empty(&gl->gl_holders));
                glock_free(gl);
                rv = 1;
                goto out;
        }
        spin_lock(&gl->gl_spin);
        gfs2_glock_schedule_for_reclaim(gl);
        spin_unlock(&gl->gl_spin);
        write_unlock(gl_lock_addr(gl->gl_hash));
out:
        return rv;
}

/**
 * search_bucket() - Find struct gfs2_glock by lock number
 * @bucket: the bucket to search
 * @name: The lock name
 *
 * Returns: NULL, or the struct gfs2_glock with the requested number
 */

static struct gfs2_glock *search_bucket(unsigned int hash,
                                        const struct gfs2_sbd *sdp,
                                        const struct lm_lockname *name)
{
        struct gfs2_glock *gl;
        struct hlist_node *h;

        hlist_for_each_entry(gl, h, &gl_hash_table[hash].hb_list, gl_list) {
                if (!lm_name_equal(&gl->gl_name, name))
                        continue;
                if (gl->gl_sbd != sdp)
                        continue;

                atomic_inc(&gl->gl_ref);

                return gl;
        }

        return NULL;
}

/**
 * may_grant - check if its ok to grant a new lock
 * @gl: The glock
 * @gh: The lock request which we wish to grant
 *
 * Returns: true if its ok to grant the lock
 */

static inline int may_grant(const struct gfs2_glock *gl, const struct gfs2_holder *gh)
{
        const struct gfs2_holder *gh_head = list_entry(gl->gl_holders.next, const struct gfs2_holder, gh_list);
        if ((gh->gh_state == LM_ST_EXCLUSIVE ||
             gh_head->gh_state == LM_ST_EXCLUSIVE) && gh != gh_head)
                return 0;
        if (gl->gl_state == gh->gh_state)
                return 1;
        if (gh->gh_flags & GL_EXACT)
                return 0;
        if (gl->gl_state == LM_ST_EXCLUSIVE) {
                if (gh->gh_state == LM_ST_SHARED && gh_head->gh_state == LM_ST_SHARED)
                        return 1;
                if (gh->gh_state == LM_ST_DEFERRED && gh_head->gh_state == LM_ST_DEFERRED)
                        return 1;
        }
        if (gl->gl_state != LM_ST_UNLOCKED && (gh->gh_flags & LM_FLAG_ANY))
                return 1;
        return 0;
}

static void gfs2_holder_wake(struct gfs2_holder *gh)
{
        clear_bit(HIF_WAIT, &gh->gh_iflags);
        smp_mb__after_clear_bit();
        wake_up_bit(&gh->gh_iflags, HIF_WAIT);
}

/**
 * do_error - Something unexpected has happened during a lock request
 *
 */

static inline void do_error(struct gfs2_glock *gl, const int ret)
{
        struct gfs2_holder *gh, *tmp;

        list_for_each_entry_safe(gh, tmp, &gl->gl_holders, gh_list) {
                if (test_bit(HIF_HOLDER, &gh->gh_iflags))
                        continue;
                if (ret & LM_OUT_ERROR)
                        gh->gh_error = -EIO;
                else if (gh->gh_flags & (LM_FLAG_TRY | LM_FLAG_TRY_1CB))
                        gh->gh_error = GLR_TRYFAILED;
                else
                        continue;
                list_del_init(&gh->gh_list);
                trace_gfs2_glock_queue(gh, 0);
                gfs2_holder_wake(gh);
        }
}

/**
 * do_promote - promote as many requests as possible on the current queue
 * @gl: The glock
 * 
 * Returns: 1 if there is a blocked holder at the head of the list, or 2
 *          if a type specific operation is underway.
 */

static int do_promote(struct gfs2_glock *gl)
__releases(&gl->gl_spin)
__acquires(&gl->gl_spin)
{
        const struct gfs2_glock_operations *glops = gl->gl_ops;
        struct gfs2_holder *gh, *tmp;
        int ret;

restart:
        list_for_each_entry_safe(gh, tmp, &gl->gl_holders, gh_list) {
                if (test_bit(HIF_HOLDER, &gh->gh_iflags))
                        continue;
                if (may_grant(gl, gh)) {
                        if (gh->gh_list.prev == &gl->gl_holders &&
                            glops->go_lock) {
                                spin_unlock(&gl->gl_spin);
                                /* FIXME: eliminate this eventually */
                                ret = glops->go_lock(gh);
                                spin_lock(&gl->gl_spin);
                                if (ret) {
                                        if (ret == 1)
                                                return 2;
                                        gh->gh_error = ret;
                                        list_del_init(&gh->gh_list);
                                        trace_gfs2_glock_queue(gh, 0);
                                        gfs2_holder_wake(gh);
                                        goto restart;
                                }
                                set_bit(HIF_HOLDER, &gh->gh_iflags);
                                trace_gfs2_promote(gh, 1);
                                gfs2_holder_wake(gh);
                                goto restart;
                        }
                        set_bit(HIF_HOLDER, &gh->gh_iflags);
                        trace_gfs2_promote(gh, 0);
                        gfs2_holder_wake(gh);
                        continue;
                }
                if (gh->gh_list.prev == &gl->gl_holders)
                        return 1;
                do_error(gl, 0);
                break;
        }
        return 0;
}

/**
 * find_first_waiter - find the first gh that's waiting for the glock
 * @gl: the glock
 */

static inline struct gfs2_holder *find_first_waiter(const struct gfs2_glock *gl)
{
        struct gfs2_holder *gh;

        list_for_each_entry(gh, &gl->gl_holders, gh_list) {
                if (!test_bit(HIF_HOLDER, &gh->gh_iflags))
                        return gh;
        }
        return NULL;
}

/**
 * state_change - record that the glock is now in a different state
 * @gl: the glock
 * @new_state the new state
 *
 */

static void state_change(struct gfs2_glock *gl, unsigned int new_state)
{
        int held1, held2;

        held1 = (gl->gl_state != LM_ST_UNLOCKED);
        held2 = (new_state != LM_ST_UNLOCKED);

        if (held1 != held2) {
                if (held2)
                        gfs2_glock_hold(gl);
                else
                        gfs2_glock_put_nolock(gl);
        }
        if (held1 && held2 && list_empty(&gl->gl_holders))
                clear_bit(GLF_QUEUED, &gl->gl_flags);

        gl->gl_state = new_state;
        gl->gl_tchange = jiffies;
}

static void gfs2_demote_wake(struct gfs2_glock *gl)
{
        gl->gl_demote_state = LM_ST_EXCLUSIVE;
        clear_bit(GLF_DEMOTE, &gl->gl_flags);
        smp_mb__after_clear_bit();
        wake_up_bit(&gl->gl_flags, GLF_DEMOTE);
}

/**
 * finish_xmote - The DLM has replied to one of our lock requests
 * @gl: The glock
 * @ret: The status from the DLM
 *
 */

static void finish_xmote(struct gfs2_glock *gl, unsigned int ret)
{
        const struct gfs2_glock_operations *glops = gl->gl_ops;
        struct gfs2_holder *gh;
        unsigned state = ret & LM_OUT_ST_MASK;
        int rv;

        spin_lock(&gl->gl_spin);
        trace_gfs2_glock_state_change(gl, state);
        state_change(gl, state);
        gh = find_first_waiter(gl);

        /* Demote to UN request arrived during demote to SH or DF */
        if (test_bit(GLF_DEMOTE_IN_PROGRESS, &gl->gl_flags) &&
            state != LM_ST_UNLOCKED && gl->gl_demote_state == LM_ST_UNLOCKED)
                gl->gl_target = LM_ST_UNLOCKED;

        /* Check for state != intended state */
        if (unlikely(state != gl->gl_target)) {
                if (gh && !test_bit(GLF_DEMOTE_IN_PROGRESS, &gl->gl_flags)) {
                        /* move to back of queue and try next entry */
                        if (ret & LM_OUT_CANCELED) {
                                if ((gh->gh_flags & LM_FLAG_PRIORITY) == 0)
                                        list_move_tail(&gh->gh_list, &gl->gl_holders);
                                gh = find_first_waiter(gl);
                                gl->gl_target = gh->gh_state;
                                goto retry;
                        }
                        /* Some error or failed "try lock" - report it */
                        if ((ret & LM_OUT_ERROR) ||
                            (gh->gh_flags & (LM_FLAG_TRY | LM_FLAG_TRY_1CB))) {
                                gl->gl_target = gl->gl_state;
                                do_error(gl, ret);
                                goto out;
                        }
                }
                switch(state) {
                /* Unlocked due to conversion deadlock, try again */
                case LM_ST_UNLOCKED:
retry:
                        do_xmote(gl, gh, gl->gl_target);
                        break;
                /* Conversion fails, unlock and try again */
                case LM_ST_SHARED:
                case LM_ST_DEFERRED:
                        do_xmote(gl, gh, LM_ST_UNLOCKED);
                        break;
                default: /* Everything else */
                        printk(KERN_ERR "GFS2: wanted %u got %u\n", gl->gl_target, state);
                        GLOCK_BUG_ON(gl, 1);
                }
                spin_unlock(&gl->gl_spin);
                return;
        }

        /* Fast path - we got what we asked for */
        if (test_and_clear_bit(GLF_DEMOTE_IN_PROGRESS, &gl->gl_flags))
                gfs2_demote_wake(gl);
        if (state != LM_ST_UNLOCKED) {
                if (glops->go_xmote_bh) {
                        spin_unlock(&gl->gl_spin);
                        rv = glops->go_xmote_bh(gl, gh);
                        spin_lock(&gl->gl_spin);
                        if (rv) {
                                do_error(gl, rv);
                                goto out;
                        }
                }
                rv = do_promote(gl);
                if (rv == 2)
                        goto out_locked;
        }
out:
        clear_bit(GLF_LOCK, &gl->gl_flags);
out_locked:
        spin_unlock(&gl->gl_spin);
}

/**
 * do_xmote - Calls the DLM to change the state of a lock
 * @gl: The lock state
 * @gh: The holder (only for promotes)
 * @target: The target lock state
 *
 */

static void do_xmote(struct gfs2_glock *gl, struct gfs2_holder *gh, unsigned int target)
__releases(&gl->gl_spin)
__acquires(&gl->gl_spin)
{
        const struct gfs2_glock_operations *glops = gl->gl_ops;
        struct gfs2_sbd *sdp = gl->gl_sbd;
        unsigned int lck_flags = gh ? gh->gh_flags : 0;
        int ret;

        lck_flags &= (LM_FLAG_TRY | LM_FLAG_TRY_1CB | LM_FLAG_NOEXP |
                      LM_FLAG_PRIORITY);
        GLOCK_BUG_ON(gl, gl->gl_state == target);
        GLOCK_BUG_ON(gl, gl->gl_state == gl->gl_target);
        if ((target == LM_ST_UNLOCKED || target == LM_ST_DEFERRED) &&
            glops->go_inval) {
                set_bit(GLF_INVALIDATE_IN_PROGRESS, &gl->gl_flags);
                do_error(gl, 0); /* Fail queued try locks */
        }
        gl->gl_req = target;
        spin_unlock(&gl->gl_spin);
        if (glops->go_xmote_th)
                glops->go_xmote_th(gl);
        if (test_bit(GLF_INVALIDATE_IN_PROGRESS, &gl->gl_flags))
                glops->go_inval(gl, target == LM_ST_DEFERRED ? 0 : DIO_METADATA);
        clear_bit(GLF_INVALIDATE_IN_PROGRESS, &gl->gl_flags);

        gfs2_glock_hold(gl);
        if (target != LM_ST_UNLOCKED && (gl->gl_state == LM_ST_SHARED ||
            gl->gl_state == LM_ST_DEFERRED) &&
            !(lck_flags & (LM_FLAG_TRY | LM_FLAG_TRY_1CB)))
                lck_flags |= LM_FLAG_TRY_1CB;

        if (sdp->sd_lockstruct.ls_ops->lm_lock) {
                /* lock_dlm */
                ret = sdp->sd_lockstruct.ls_ops->lm_lock(gl, target, lck_flags);
                GLOCK_BUG_ON(gl, ret);
        } else { /* lock_nolock */
                finish_xmote(gl, target);
                if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
                        gfs2_glock_put(gl);
        }

        spin_lock(&gl->gl_spin);
}

/**
 * find_first_holder - find the first "holder" gh
 * @gl: the glock
 */

static inline struct gfs2_holder *find_first_holder(const struct gfs2_glock *gl)
{
        struct gfs2_holder *gh;

        if (!list_empty(&gl->gl_holders)) {
                gh = list_entry(gl->gl_holders.next, struct gfs2_holder, gh_list);
                if (test_bit(HIF_HOLDER, &gh->gh_iflags))
                        return gh;
        }
        return NULL;
}

/**
 * run_queue - do all outstanding tasks related to a glock
 * @gl: The glock in question
 * @nonblock: True if we must not block in run_queue
 *
 */

static void run_queue(struct gfs2_glock *gl, const int nonblock)
__releases(&gl->gl_spin)
__acquires(&gl->gl_spin)
{
        struct gfs2_holder *gh = NULL;
        int ret;

        if (test_and_set_bit(GLF_LOCK, &gl->gl_flags))
                return;

        GLOCK_BUG_ON(gl, test_bit(GLF_DEMOTE_IN_PROGRESS, &gl->gl_flags));

        if (test_bit(GLF_DEMOTE, &gl->gl_flags) &&
            gl->gl_demote_state != gl->gl_state) {
                if (find_first_holder(gl))
                        goto out_unlock;
                if (nonblock)
                        goto out_sched;
                set_bit(GLF_DEMOTE_IN_PROGRESS, &gl->gl_flags);
                GLOCK_BUG_ON(gl, gl->gl_demote_state == LM_ST_EXCLUSIVE);
                gl->gl_target = gl->gl_demote_state;
        } else {
                if (test_bit(GLF_DEMOTE, &gl->gl_flags))
                        gfs2_demote_wake(gl);
                ret = do_promote(gl);
                if (ret == 0)
                        goto out_unlock;
                if (ret == 2)
                        goto out;
                gh = find_first_waiter(gl);
                gl->gl_target = gh->gh_state;
                if (!(gh->gh_flags & (LM_FLAG_TRY | LM_FLAG_TRY_1CB)))
                        do_error(gl, 0); /* Fail queued try locks */
        }
        do_xmote(gl, gh, gl->gl_target);
out:
        return;

out_sched:
        clear_bit(GLF_LOCK, &gl->gl_flags);
        smp_mb__after_clear_bit();
        gfs2_glock_hold(gl);
        if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
                gfs2_glock_put_nolock(gl);
        return;

out_unlock:
        clear_bit(GLF_LOCK, &gl->gl_flags);
        smp_mb__after_clear_bit();
        return;
}

static void delete_work_func(struct work_struct *work)
{
        struct gfs2_glock *gl = container_of(work, struct gfs2_glock, gl_delete);
        struct gfs2_sbd *sdp = gl->gl_sbd;
        struct gfs2_inode *ip;
        struct inode *inode;
        u64 no_addr = gl->gl_name.ln_number;

        ip = gl->gl_object;
        /* Note: Unsafe to dereference ip as we don't hold right refs/locks */

        if (ip)
                inode = gfs2_ilookup(sdp->sd_vfs, no_addr);
        else
                inode = gfs2_lookup_by_inum(sdp, no_addr, NULL, GFS2_BLKST_UNLINKED);
        if (inode && !IS_ERR(inode)) {
                d_prune_aliases(inode);
                iput(inode);
        }
        gfs2_glock_put(gl);
}

static void glock_work_func(struct work_struct *work)
{
        unsigned long delay = 0;
        struct gfs2_glock *gl = container_of(work, struct gfs2_glock, gl_work.work);
        int drop_ref = 0;

        if (test_and_clear_bit(GLF_REPLY_PENDING, &gl->gl_flags)) {
                finish_xmote(gl, gl->gl_reply);
                drop_ref = 1;
        }
        spin_lock(&gl->gl_spin);
        if (test_and_clear_bit(GLF_PENDING_DEMOTE, &gl->gl_flags) &&
            gl->gl_state != LM_ST_UNLOCKED &&
            gl->gl_demote_state != LM_ST_EXCLUSIVE) {
                unsigned long holdtime, now = jiffies;
                holdtime = gl->gl_tchange + gl->gl_ops->go_min_hold_time;
                if (time_before(now, holdtime))
                        delay = holdtime - now;
                set_bit(delay ? GLF_PENDING_DEMOTE : GLF_DEMOTE, &gl->gl_flags);
        }
        run_queue(gl, 0);
        spin_unlock(&gl->gl_spin);
        if (!delay ||
            queue_delayed_work(glock_workqueue, &gl->gl_work, delay) == 0)
                gfs2_glock_put(gl);
        if (drop_ref)
                gfs2_glock_put(gl);
}

/**
 * gfs2_glock_get() - Get a glock, or create one if one doesn't exist
 * @sdp: The GFS2 superblock
 * @number: the lock number
 * @glops: The glock_operations to use
 * @create: If 0, don't create the glock if it doesn't exist
 * @glp: the glock is returned here
 *
 * This does not lock a glock, just finds/creates structures for one.
 *
 * Returns: errno
 */

int gfs2_glock_get(struct gfs2_sbd *sdp, u64 number,
                   const struct gfs2_glock_operations *glops, int create,
                   struct gfs2_glock **glp)
{
        struct super_block *s = sdp->sd_vfs;
        struct lm_lockname name = { .ln_number = number, .ln_type = glops->go_type };
        struct gfs2_glock *gl, *tmp;
        unsigned int hash = gl_hash(sdp, &name);
        struct address_space *mapping;

        read_lock(gl_lock_addr(hash));
        gl = search_bucket(hash, sdp, &name);
        read_unlock(gl_lock_addr(hash));

        *glp = gl;
        if (gl)
                return 0;
        if (!create)
                return -ENOENT;

        if (glops->go_flags & GLOF_ASPACE)
                gl = kmem_cache_alloc(gfs2_glock_aspace_cachep, GFP_KERNEL);
        else
                gl = kmem_cache_alloc(gfs2_glock_cachep, GFP_KERNEL);
        if (!gl)
                return -ENOMEM;

        atomic_inc(&sdp->sd_glock_disposal);
        gl->gl_flags = 0;
        gl->gl_name = name;
        atomic_set(&gl->gl_ref, 1);
        gl->gl_state = LM_ST_UNLOCKED;
        gl->gl_target = LM_ST_UNLOCKED;
        gl->gl_demote_state = LM_ST_EXCLUSIVE;
        gl->gl_hash = hash;
        gl->gl_ops = glops;
        snprintf(gl->gl_strname, GDLM_STRNAME_BYTES, "%8x%16llx", name.ln_type, (unsigned long long)number);
        memset(&gl->gl_lksb, 0, sizeof(struct dlm_lksb));
        gl->gl_lksb.sb_lvbptr = gl->gl_lvb;
        gl->gl_tchange = jiffies;
        gl->gl_object = NULL;
        gl->gl_sbd = sdp;
        INIT_DELAYED_WORK(&gl->gl_work, glock_work_func);
        INIT_WORK(&gl->gl_delete, delete_work_func);

        mapping = gfs2_glock2aspace(gl);
        if (mapping) {
                mapping->a_ops = &gfs2_meta_aops;
                mapping->host = s->s_bdev->bd_inode;
                mapping->flags = 0;
                mapping_set_gfp_mask(mapping, GFP_NOFS);
                mapping->assoc_mapping = NULL;
                mapping->backing_dev_info = s->s_bdi;
                mapping->writeback_index = 0;
        }

        write_lock(gl_lock_addr(hash));
        tmp = search_bucket(hash, sdp, &name);
        if (tmp) {
                write_unlock(gl_lock_addr(hash));
                glock_free(gl);
                gl = tmp;
        } else {
                hlist_add_head(&gl->gl_list, &gl_hash_table[hash].hb_list);
                write_unlock(gl_lock_addr(hash));
        }

        *glp = gl;

        return 0;
}

/**
 * gfs2_holder_init - initialize a struct gfs2_holder in the default way
 * @gl: the glock
 * @state: the state we're requesting
 * @flags: the modifier flags
 * @gh: the holder structure
 *
 */

void gfs2_holder_init(struct gfs2_glock *gl, unsigned int state, unsigned flags,
                      struct gfs2_holder *gh)
{
        INIT_LIST_HEAD(&gh->gh_list);
        gh->gh_gl = gl;
        gh->gh_ip = (unsigned long)__builtin_return_address(0);
        gh->gh_owner_pid = get_pid(task_pid(current));
        gh->gh_state = state;
        gh->gh_flags = flags;
        gh->gh_error = 0;
        gh->gh_iflags = 0;
        gfs2_glock_hold(gl);
}

/**
 * gfs2_holder_reinit - reinitialize a struct gfs2_holder so we can requeue it
 * @state: the state we're requesting
 * @flags: the modifier flags
 * @gh: the holder structure
 *
 * Don't mess with the glock.
 *
 */

void gfs2_holder_reinit(unsigned int state, unsigned flags, struct gfs2_holder *gh)
{
        gh->gh_state = state;
        gh->gh_flags = flags;
        gh->gh_iflags = 0;
        gh->gh_ip = (unsigned long)__builtin_return_address(0);
        if (gh->gh_owner_pid)
                put_pid(gh->gh_owner_pid);
        gh->gh_owner_pid = get_pid(task_pid(current));
}

/**
 * gfs2_holder_uninit - uninitialize a holder structure (drop glock reference)
 * @gh: the holder structure
 *
 */

void gfs2_holder_uninit(struct gfs2_holder *gh)
{
        put_pid(gh->gh_owner_pid);
        gfs2_glock_put(gh->gh_gl);
        gh->gh_gl = NULL;
        gh->gh_ip = 0;
}

/**
 * gfs2_glock_holder_wait
 * @word: unused
 *
 * This function and gfs2_glock_demote_wait both show up in the WCHAN
 * field. Thus I've separated these otherwise identical functions in
 * order to be more informative to the user.
 */

static int gfs2_glock_holder_wait(void *word)
{
        schedule();
        return 0;
}

static int gfs2_glock_demote_wait(void *word)
{
        schedule();
        return 0;
}

static void wait_on_holder(struct gfs2_holder *gh)
{
        might_sleep();
        wait_on_bit(&gh->gh_iflags, HIF_WAIT, gfs2_glock_holder_wait, TASK_UNINTERRUPTIBLE);
}

static void wait_on_demote(struct gfs2_glock *gl)
{
        might_sleep();
        wait_on_bit(&gl->gl_flags, GLF_DEMOTE, gfs2_glock_demote_wait, TASK_UNINTERRUPTIBLE);
}

/**
 * handle_callback - process a demote request
 * @gl: the glock
 * @state: the state the caller wants us to change to
 *
 * There are only two requests that we are going to see in actual
 * practise: LM_ST_SHARED and LM_ST_UNLOCKED
 */

static void handle_callback(struct gfs2_glock *gl, unsigned int state,
                            unsigned long delay)
{
        int bit = delay ? GLF_PENDING_DEMOTE : GLF_DEMOTE;

        set_bit(bit, &gl->gl_flags);
        if (gl->gl_demote_state == LM_ST_EXCLUSIVE) {
                gl->gl_demote_state = state;
                gl->gl_demote_time = jiffies;
        } else if (gl->gl_demote_state != LM_ST_UNLOCKED &&
                        gl->gl_demote_state != state) {
                gl->gl_demote_state = LM_ST_UNLOCKED;
        }
        if (gl->gl_ops->go_callback)
                gl->gl_ops->go_callback(gl);
        trace_gfs2_demote_rq(gl);
}

/**
 * gfs2_glock_wait - wait on a glock acquisition
 * @gh: the glock holder
 *
 * Returns: 0 on success
 */

int gfs2_glock_wait(struct gfs2_holder *gh)
{
        wait_on_holder(gh);
        return gh->gh_error;
}

void gfs2_print_dbg(struct seq_file *seq, const char *fmt, ...)
{
        struct va_format vaf;
        va_list args;

        va_start(args, fmt);

        if (seq) {
                struct gfs2_glock_iter *gi = seq->private;
                vsprintf(gi->string, fmt, args);
                seq_printf(seq, gi->string);
        } else {
                vaf.fmt = fmt;
                vaf.va = &args;

                printk(KERN_ERR " %pV", &vaf);
        }

        va_end(args);
}

/**
 * add_to_queue - Add a holder to the wait queue (but look for recursion)
 * @gh: the holder structure to add
 *
 * Eventually we should move the recursive locking trap to a
 * debugging option or something like that. This is the fast
 * path and needs to have the minimum number of distractions.
 * 
 */

static inline void add_to_queue(struct gfs2_holder *gh)
__releases(&gl->gl_spin)
__acquires(&gl->gl_spin)
{
        struct gfs2_glock *gl = gh->gh_gl;
        struct gfs2_sbd *sdp = gl->gl_sbd;
        struct list_head *insert_pt = NULL;
        struct gfs2_holder *gh2;
        int try_lock = 0;

        BUG_ON(gh->gh_owner_pid == NULL);
        if (test_and_set_bit(HIF_WAIT, &gh->gh_iflags))
                BUG();

        if (gh->gh_flags & (LM_FLAG_TRY | LM_FLAG_TRY_1CB)) {
                if (test_bit(GLF_LOCK, &gl->gl_flags))
                        try_lock = 1;
                if (test_bit(GLF_INVALIDATE_IN_PROGRESS, &gl->gl_flags))
                        goto fail;
        }

        list_for_each_entry(gh2, &gl->gl_holders, gh_list) {
                if (unlikely(gh2->gh_owner_pid == gh->gh_owner_pid &&
                    (gh->gh_gl->gl_ops->go_type != LM_TYPE_FLOCK)))
                        goto trap_recursive;
                if (try_lock &&
                    !(gh2->gh_flags & (LM_FLAG_TRY | LM_FLAG_TRY_1CB)) &&
                    !may_grant(gl, gh)) {
fail:
                        gh->gh_error = GLR_TRYFAILED;
                        gfs2_holder_wake(gh);
                        return;
                }
                if (test_bit(HIF_HOLDER, &gh2->gh_iflags))
                        continue;
                if (unlikely((gh->gh_flags & LM_FLAG_PRIORITY) && !insert_pt))
                        insert_pt = &gh2->gh_list;
        }
        set_bit(GLF_QUEUED, &gl->gl_flags);
        if (likely(insert_pt == NULL)) {
                list_add_tail(&gh->gh_list, &gl->gl_holders);
                if (unlikely(gh->gh_flags & LM_FLAG_PRIORITY))
                        goto do_cancel;
                return;
        }
        trace_gfs2_glock_queue(gh, 1);
        list_add_tail(&gh->gh_list, insert_pt);
do_cancel:
        gh = list_entry(gl->gl_holders.next, struct gfs2_holder, gh_list);
        if (!(gh->gh_flags & LM_FLAG_PRIORITY)) {
                spin_unlock(&gl->gl_spin);
                if (sdp->sd_lockstruct.ls_ops->lm_cancel)
                        sdp->sd_lockstruct.ls_ops->lm_cancel(gl);
                spin_lock(&gl->gl_spin);
        }
        return;

trap_recursive:
        print_symbol(KERN_ERR "original: %s\n", gh2->gh_ip);
        printk(KERN_ERR "pid: %d\n", pid_nr(gh2->gh_owner_pid));
        printk(KERN_ERR "lock type: %d req lock state : %d\n",
               gh2->gh_gl->gl_name.ln_type, gh2->gh_state);
        print_symbol(KERN_ERR "new: %s\n", gh->gh_ip);
        printk(KERN_ERR "pid: %d\n", pid_nr(gh->gh_owner_pid));
        printk(KERN_ERR "lock type: %d req lock state : %d\n",
               gh->gh_gl->gl_name.ln_type, gh->gh_state);
        __dump_glock(NULL, gl);
        BUG();
}

/**
 * gfs2_glock_nq - enqueue a struct gfs2_holder onto a glock (acquire a glock)
 * @gh: the holder structure
 *
 * if (gh->gh_flags & GL_ASYNC), this never returns an error
 *
 * Returns: 0, GLR_TRYFAILED, or errno on failure
 */

int gfs2_glock_nq(struct gfs2_holder *gh)
{
        struct gfs2_glock *gl = gh->gh_gl;
        struct gfs2_sbd *sdp = gl->gl_sbd;
        int error = 0;

        if (unlikely(test_bit(SDF_SHUTDOWN, &sdp->sd_flags)))
                return -EIO;

        spin_lock(&gl->gl_spin);
        add_to_queue(gh);
        if ((LM_FLAG_NOEXP & gh->gh_flags) &&
            test_and_clear_bit(GLF_FROZEN, &gl->gl_flags))
                set_bit(GLF_REPLY_PENDING, &gl->gl_flags);
        run_queue(gl, 1);
        spin_unlock(&gl->gl_spin);

        if (!(gh->gh_flags & GL_ASYNC))
                error = gfs2_glock_wait(gh);

        return error;
}

/**
 * gfs2_glock_poll - poll to see if an async request has been completed
 * @gh: the holder
 *
 * Returns: 1 if the request is ready to be gfs2_glock_wait()ed on
 */

int gfs2_glock_poll(struct gfs2_holder *gh)
{
        return test_bit(HIF_WAIT, &gh->gh_iflags) ? 0 : 1;
}

/**
 * gfs2_glock_dq - dequeue a struct gfs2_holder from a glock (release a glock)
 * @gh: the glock holder
 *
 */

void gfs2_glock_dq(struct gfs2_holder *gh)
{
        struct gfs2_glock *gl = gh->gh_gl;
        const struct gfs2_glock_operations *glops = gl->gl_ops;
        unsigned delay = 0;
        int fast_path = 0;

        spin_lock(&gl->gl_spin);
        if (gh->gh_flags & GL_NOCACHE)
                handle_callback(gl, LM_ST_UNLOCKED, 0);

        list_del_init(&gh->gh_list);
        if (find_first_holder(gl) == NULL) {
                if (glops->go_unlock) {
                        GLOCK_BUG_ON(gl, test_and_set_bit(GLF_LOCK, &gl->gl_flags));
                        spin_unlock(&gl->gl_spin);
                        glops->go_unlock(gh);
                        spin_lock(&gl->gl_spin);
                        clear_bit(GLF_LOCK, &gl->gl_flags);
                }
                if (list_empty(&gl->gl_holders) &&
                    !test_bit(GLF_PENDING_DEMOTE, &gl->gl_flags) &&
                    !test_bit(GLF_DEMOTE, &gl->gl_flags))
                        fast_path = 1;
        }
        trace_gfs2_glock_queue(gh, 0);
        spin_unlock(&gl->gl_spin);
        if (likely(fast_path))
                return;

        gfs2_glock_hold(gl);
        if (test_bit(GLF_PENDING_DEMOTE, &gl->gl_flags) &&
            !test_bit(GLF_DEMOTE, &gl->gl_flags))
                delay = gl->gl_ops->go_min_hold_time;
        if (queue_delayed_work(glock_workqueue, &gl->gl_work, delay) == 0)
                gfs2_glock_put(gl);
}

void gfs2_glock_dq_wait(struct gfs2_holder *gh)
{
        struct gfs2_glock *gl = gh->gh_gl;
        gfs2_glock_dq(gh);
        wait_on_demote(gl);
}

/**
 * gfs2_glock_dq_uninit - dequeue a holder from a glock and initialize it
 * @gh: the holder structure
 *
 */

void gfs2_glock_dq_uninit(struct gfs2_holder *gh)
{
        gfs2_glock_dq(gh);
        gfs2_holder_uninit(gh);
}

/**
 * gfs2_glock_nq_num - acquire a glock based on lock number
 * @sdp: the filesystem
 * @number: the lock number
 * @glops: the glock operations for the type of glock
 * @state: the state to acquire the glock in
 * @flags: modifier flags for the aquisition
 * @gh: the struct gfs2_holder
 *
 * Returns: errno
 */

int gfs2_glock_nq_num(struct gfs2_sbd *sdp, u64 number,
                      const struct gfs2_glock_operations *glops,
                      unsigned int state, int flags, struct gfs2_holder *gh)
{
        struct gfs2_glock *gl;
        int error;

        error = gfs2_glock_get(sdp, number, glops, CREATE, &gl);
        if (!error) {
                error = gfs2_glock_nq_init(gl, state, flags, gh);
                gfs2_glock_put(gl);
        }

        return error;
}

/**
 * glock_compare - Compare two struct gfs2_glock structures for sorting
 * @arg_a: the first structure
 * @arg_b: the second structure
 *
 */

static int glock_compare(const void *arg_a, const void *arg_b)
{
        const struct gfs2_holder *gh_a = *(const struct gfs2_holder **)arg_a;
        const struct gfs2_holder *gh_b = *(const struct gfs2_holder **)arg_b;
        const struct lm_lockname *a = &gh_a->gh_gl->gl_name;
        const struct lm_lockname *b = &gh_b->gh_gl->gl_name;

        if (a->ln_number > b->ln_number)
                return 1;
        if (a->ln_number < b->ln_number)
                return -1;
        BUG_ON(gh_a->gh_gl->gl_ops->go_type == gh_b->gh_gl->gl_ops->go_type);
        return 0;
}

/**
 * nq_m_sync - synchonously acquire more than one glock in deadlock free order
 * @num_gh: the number of structures
 * @ghs: an array of struct gfs2_holder structures
 *
 * Returns: 0 on success (all glocks acquired),
 *          errno on failure (no glocks acquired)
 */

static int nq_m_sync(unsigned int num_gh, struct gfs2_holder *ghs,
                     struct gfs2_holder **p)
{
        unsigned int x;
        int error = 0;

        for (x = 0; x < num_gh; x++)
                p[x] = &ghs[x];

        sort(p, num_gh, sizeof(struct gfs2_holder *), glock_compare, NULL);

        for (x = 0; x < num_gh; x++) {
                p[x]->gh_flags &= ~(LM_FLAG_TRY | GL_ASYNC);

                error = gfs2_glock_nq(p[x]);
                if (error) {
                        while (x--)
                                gfs2_glock_dq(p[x]);
                        break;
                }
        }

        return error;
}

/**
 * gfs2_glock_nq_m - acquire multiple glocks
 * @num_gh: the number of structures
 * @ghs: an array of struct gfs2_holder structures
 *
 *
 * Returns: 0 on success (all glocks acquired),
 *          errno on failure (no glocks acquired)
 */

int gfs2_glock_nq_m(unsigned int num_gh, struct gfs2_holder *ghs)
{
        struct gfs2_holder *tmp[4];
        struct gfs2_holder **pph = tmp;
        int error = 0;

        switch(num_gh) {
        case 0:
                return 0;
        case 1:
                ghs->gh_flags &= ~(LM_FLAG_TRY | GL_ASYNC);
                return gfs2_glock_nq(ghs);
        default:
                if (num_gh <= 4)
                        break;
                pph = kmalloc(num_gh * sizeof(struct gfs2_holder *), GFP_NOFS);
                if (!pph)
                        return -ENOMEM;
        }

        error = nq_m_sync(num_gh, ghs, pph);

        if (pph != tmp)
                kfree(pph);

        return error;
}

/**
 * gfs2_glock_dq_m - release multiple glocks
 * @num_gh: the number of structures
 * @ghs: an array of struct gfs2_holder structures
 *
 */

void gfs2_glock_dq_m(unsigned int num_gh, struct gfs2_holder *ghs)
{
        unsigned int x;

        for (x = 0; x < num_gh; x++)
                gfs2_glock_dq(&ghs[x]);
}

/**
 * gfs2_glock_dq_uninit_m - release multiple glocks
 * @num_gh: the number of structures
 * @ghs: an array of struct gfs2_holder structures
 *
 */

void gfs2_glock_dq_uninit_m(unsigned int num_gh, struct gfs2_holder *ghs)
{
        unsigned int x;

        for (x = 0; x < num_gh; x++)
                gfs2_glock_dq_uninit(&ghs[x]);
}

void gfs2_glock_cb(struct gfs2_glock *gl, unsigned int state)
{
        unsigned long delay = 0;
        unsigned long holdtime;
        unsigned long now = jiffies;

        gfs2_glock_hold(gl);
        holdtime = gl->gl_tchange + gl->gl_ops->go_min_hold_time;
        if (test_bit(GLF_QUEUED, &gl->gl_flags)) {
                if (time_before(now, holdtime))
                        delay = holdtime - now;
                if (test_bit(GLF_REPLY_PENDING, &gl->gl_flags))
                        delay = gl->gl_ops->go_min_hold_time;
        }

        spin_lock(&gl->gl_spin);
        handle_callback(gl, state, delay);
        spin_unlock(&gl->gl_spin);
        if (queue_delayed_work(glock_workqueue, &gl->gl_work, delay) == 0)
                gfs2_glock_put(gl);
}

/**
 * gfs2_should_freeze - Figure out if glock should be frozen
 * @gl: The glock in question
 *
 * Glocks are not frozen if (a) the result of the dlm operation is
 * an error, (b) the locking operation was an unlock operation or
 * (c) if there is a "noexp" flagged request anywhere in the queue
 *
 * Returns: 1 if freezing should occur, 0 otherwise
 */

static int gfs2_should_freeze(const struct gfs2_glock *gl)
{
        const struct gfs2_holder *gh;

        if (gl->gl_reply & ~LM_OUT_ST_MASK)
                return 0;
        if (gl->gl_target == LM_ST_UNLOCKED)
                return 0;

        list_for_each_entry(gh, &gl->gl_holders, gh_list) {
                if (test_bit(HIF_HOLDER, &gh->gh_iflags))
                        continue;
                if (LM_FLAG_NOEXP & gh->gh_flags)
                        return 0;
        }

        return 1;
}

/**
 * gfs2_glock_complete - Callback used by locking
 * @gl: Pointer to the glock
 * @ret: The return value from the dlm
 *
 * The gl_reply field is under the gl_spin lock so that it is ok
 * to use a bitfield shared with other glock state fields.
 */

void gfs2_glock_complete(struct gfs2_glock *gl, int ret)
{
        struct lm_lockstruct *ls = &gl->gl_sbd->sd_lockstruct;

        spin_lock(&gl->gl_spin);
        gl->gl_reply = ret;

        if (unlikely(test_bit(DFL_BLOCK_LOCKS, &ls->ls_flags))) {
                if (gfs2_should_freeze(gl)) {
                        set_bit(GLF_FROZEN, &gl->gl_flags);
                        spin_unlock(&gl->gl_spin);
                        return;
                }
        }

        spin_unlock(&gl->gl_spin);
        set_bit(GLF_REPLY_PENDING, &gl->gl_flags);
        smp_wmb();
        gfs2_glock_hold(gl);
        if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
                gfs2_glock_put(gl);
}


static int gfs2_shrink_glock_memory(struct shrinker *shrink, int nr, gfp_t gfp_mask)
{
        struct gfs2_glock *gl;
        int may_demote;
        int nr_skipped = 0;
        LIST_HEAD(skipped);

        if (nr == 0)
                goto out;

        if (!(gfp_mask & __GFP_FS))
                return -1;

        spin_lock(&lru_lock);
        while(nr && !list_empty(&lru_list)) {
                gl = list_entry(lru_list.next, struct gfs2_glock, gl_lru);
                list_del_init(&gl->gl_lru);
                atomic_dec(&lru_count);

                /* Test for being demotable */
                if (!test_and_set_bit(GLF_LOCK, &gl->gl_flags)) {
                        gfs2_glock_hold(gl);
                        spin_unlock(&lru_lock);
                        spin_lock(&gl->gl_spin);
                        may_demote = demote_ok(gl);
                        if (may_demote) {
                                handle_callback(gl, LM_ST_UNLOCKED, 0);
                                nr--;
                        }
                        clear_bit(GLF_LOCK, &gl->gl_flags);
                        smp_mb__after_clear_bit();
                        if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
                                gfs2_glock_put_nolock(gl);
                        spin_unlock(&gl->gl_spin);
                        spin_lock(&lru_lock);
                        continue;
                }
                nr_skipped++;
                list_add(&gl->gl_lru, &skipped);
        }
        list_splice(&skipped, &lru_list);
        atomic_add(nr_skipped, &lru_count);
        spin_unlock(&lru_lock);
out:
        return (atomic_read(&lru_count) / 100) * sysctl_vfs_cache_pressure;
}

static struct shrinker glock_shrinker = {
        .shrink = gfs2_shrink_glock_memory,
        .seeks = DEFAULT_SEEKS,
};

/**
 * examine_bucket - Call a function for glock in a hash bucket
 * @examiner: the function
 * @sdp: the filesystem
 * @bucket: the bucket
 *
 * Returns: 1 if the bucket has entries
 */

static int examine_bucket(glock_examiner examiner, struct gfs2_sbd *sdp,
                          unsigned int hash)
{
        struct gfs2_glock *gl, *prev = NULL;
        int has_entries = 0;
        struct hlist_head *head = &gl_hash_table[hash].hb_list;

        read_lock(gl_lock_addr(hash));
        /* Can't use hlist_for_each_entry - don't want prefetch here */
        if (hlist_empty(head))
                goto out;
        gl = list_entry(head->first, struct gfs2_glock, gl_list);
        while(1) {
                if (!sdp || gl->gl_sbd == sdp) {
                        gfs2_glock_hold(gl);
                        read_unlock(gl_lock_addr(hash));
                        if (prev)
                                gfs2_glock_put(prev);
                        prev = gl;
                        examiner(gl);
                        has_entries = 1;
                        read_lock(gl_lock_addr(hash));
                }
                if (gl->gl_list.next == NULL)
                        break;
                gl = list_entry(gl->gl_list.next, struct gfs2_glock, gl_list);
        }
out:
        read_unlock(gl_lock_addr(hash));
        if (prev)
                gfs2_glock_put(prev);
        cond_resched();
        return has_entries;
}


/**
 * thaw_glock - thaw out a glock which has an unprocessed reply waiting
 * @gl: The glock to thaw
 *
 * N.B. When we freeze a glock, we leave a ref to the glock outstanding,
 * so this has to result in the ref count being dropped by one.
 */

static void thaw_glock(struct gfs2_glock *gl)
{
        if (!test_and_clear_bit(GLF_FROZEN, &gl->gl_flags))
                return;
        set_bit(GLF_REPLY_PENDING, &gl->gl_flags);
        gfs2_glock_hold(gl);
        if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
                gfs2_glock_put(gl);
}

/**
 * clear_glock - look at a glock and see if we can free it from glock cache
 * @gl: the glock to look at
 *
 */

static void clear_glock(struct gfs2_glock *gl)
{
        spin_lock(&lru_lock);
        if (!list_empty(&gl->gl_lru)) {
                list_del_init(&gl->gl_lru);
                atomic_dec(&lru_count);
        }
        spin_unlock(&lru_lock);

        spin_lock(&gl->gl_spin);
        if (gl->gl_state != LM_ST_UNLOCKED)
                handle_callback(gl, LM_ST_UNLOCKED, 0);
        spin_unlock(&gl->gl_spin);
        gfs2_glock_hold(gl);
        if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
                gfs2_glock_put(gl);
}

/**
 * gfs2_glock_thaw - Thaw any frozen glocks
 * @sdp: The super block
 *
 */

void gfs2_glock_thaw(struct gfs2_sbd *sdp)
{
        unsigned x;

        for (x = 0; x < GFS2_GL_HASH_SIZE; x++)
                examine_bucket(thaw_glock, sdp, x);
}

/**
 * gfs2_gl_hash_clear - Empty out the glock hash table
 * @sdp: the filesystem
 * @wait: wait until it's all gone
 *
 * Called when unmounting the filesystem.
 */

void gfs2_gl_hash_clear(struct gfs2_sbd *sdp)
{
        unsigned int x;

        for (x = 0; x < GFS2_GL_HASH_SIZE; x++)
                examine_bucket(clear_glock, sdp, x);
        flush_workqueue(glock_workqueue);
        wait_event(sdp->sd_glock_wait, atomic_read(&sdp->sd_glock_disposal) == 0);
        gfs2_dump_lockstate(sdp);
}

void gfs2_glock_finish_truncate(struct gfs2_inode *ip)
{
        struct gfs2_glock *gl = ip->i_gl;
        int ret;

        ret = gfs2_truncatei_resume(ip);
        gfs2_assert_withdraw(gl->gl_sbd, ret == 0);

        spin_lock(&gl->gl_spin);
        clear_bit(GLF_LOCK, &gl->gl_flags);
        run_queue(gl, 1);
        spin_unlock(&gl->gl_spin);
}

static const char *state2str(unsigned state)
{
        switch(state) {
        case LM_ST_UNLOCKED:
                return "UN";
        case LM_ST_SHARED:
                return "SH";
        case LM_ST_DEFERRED:
                return "DF";
        case LM_ST_EXCLUSIVE:
                return "EX";
        }
        return "??";
}

static const char *hflags2str(char *buf, unsigned flags, unsigned long iflags)
{
        char *p = buf;
        if (flags & LM_FLAG_TRY)
                *p++ = 't';
        if (flags & LM_FLAG_TRY_1CB)
                *p++ = 'T';
        if (flags & LM_FLAG_NOEXP)
                *p++ = 'e';
        if (flags & LM_FLAG_ANY)
                *p++ = 'A';
        if (flags & LM_FLAG_PRIORITY)
                *p++ = 'p';
        if (flags & GL_ASYNC)
                *p++ = 'a';
        if (flags & GL_EXACT)
                *p++ = 'E';
        if (flags & GL_NOCACHE)
                *p++ = 'c';
        if (test_bit(HIF_HOLDER, &iflags))
                *p++ = 'H';
        if (test_bit(HIF_WAIT, &iflags))
                *p++ = 'W';
        if (test_bit(HIF_FIRST, &iflags))
                *p++ = 'F';
        *p = 0;
        return buf;
}

/**
 * dump_holder - print information about a glock holder
 * @seq: the seq_file struct
 * @gh: the glock holder
 *
 * Returns: 0 on success, -ENOBUFS when we run out of space
 */

static int dump_holder(struct seq_file *seq, const struct gfs2_holder *gh)
{
        struct task_struct *gh_owner = NULL;
        char flags_buf[32];

        if (gh->gh_owner_pid)
                gh_owner = pid_task(gh->gh_owner_pid, PIDTYPE_PID);
        gfs2_print_dbg(seq, " H: s:%s f:%s e:%d p:%ld [%s] %pS\n",
                       state2str(gh->gh_state),
                       hflags2str(flags_buf, gh->gh_flags, gh->gh_iflags),
                       gh->gh_error,
                       gh->gh_owner_pid ? (long)pid_nr(gh->gh_owner_pid) : -1,
                       gh_owner ? gh_owner->comm : "(ended)",
                       (void *)gh->gh_ip);
        return 0;
}

static const char *gflags2str(char *buf, const unsigned long *gflags)
{
        char *p = buf;
        if (test_bit(GLF_LOCK, gflags))
                *p++ = 'l';
        if (test_bit(GLF_DEMOTE, gflags))
                *p++ = 'D';
        if (test_bit(GLF_PENDING_DEMOTE, gflags))
                *p++ = 'd';
        if (test_bit(GLF_DEMOTE_IN_PROGRESS, gflags))
                *p++ = 'p';
        if (test_bit(GLF_DIRTY, gflags))
                *p++ = 'y';
        if (test_bit(GLF_LFLUSH, gflags))
                *p++ = 'f';
        if (test_bit(GLF_INVALIDATE_IN_PROGRESS, gflags))
                *p++ = 'i';
        if (test_bit(GLF_REPLY_PENDING, gflags))
                *p++ = 'r';
        if (test_bit(GLF_INITIAL, gflags))
                *p++ = 'I';
        if (test_bit(GLF_FROZEN, gflags))
                *p++ = 'F';
        if (test_bit(GLF_QUEUED, gflags))
                *p++ = 'q';
        *p = 0;
        return buf;
}

/**
 * __dump_glock - print information about a glock
 * @seq: The seq_file struct
 * @gl: the glock
 *
 * The file format is as follows:
 * One line per object, capital letters are used to indicate objects
 * G = glock, I = Inode, R = rgrp, H = holder. Glocks are not indented,
 * other objects are indented by a single space and follow the glock to
 * which they are related. Fields are indicated by lower case letters
 * followed by a colon and the field value, except for strings which are in
 * [] so that its possible to see if they are composed of spaces for
 * example. The field's are n = number (id of the object), f = flags,
 * t = type, s = state, r = refcount, e = error, p = pid.
 *
 * Returns: 0 on success, -ENOBUFS when we run out of space
 */

static int __dump_glock(struct seq_file *seq, const struct gfs2_glock *gl)
{
        const struct gfs2_glock_operations *glops = gl->gl_ops;
        unsigned long long dtime;
        const struct gfs2_holder *gh;
        char gflags_buf[32];
        int error = 0;

        dtime = jiffies - gl->gl_demote_time;
        dtime *= 1000000/HZ; /* demote time in uSec */
        if (!test_bit(GLF_DEMOTE, &gl->gl_flags))
                dtime = 0;
        gfs2_print_dbg(seq, "G:  s:%s n:%u/%llx f:%s t:%s d:%s/%llu a:%d r:%d\n",
                  state2str(gl->gl_state),
                  gl->gl_name.ln_type,
                  (unsigned long long)gl->gl_name.ln_number,
                  gflags2str(gflags_buf, &gl->gl_flags),
                  state2str(gl->gl_target),
                  state2str(gl->gl_demote_state), dtime,
                  atomic_read(&gl->gl_ail_count),
                  atomic_read(&gl->gl_ref));

        list_for_each_entry(gh, &gl->gl_holders, gh_list) {
                error = dump_holder(seq, gh);
                if (error)
                        goto out;
        }
        if (gl->gl_state != LM_ST_UNLOCKED && glops->go_dump)
                error = glops->go_dump(seq, gl);
out:
        return error;
}

static int dump_glock(struct seq_file *seq, struct gfs2_glock *gl)
{
        int ret;
        spin_lock(&gl->gl_spin);
        ret = __dump_glock(seq, gl);
        spin_unlock(&gl->gl_spin);
        return ret;
}

/**
 * gfs2_dump_lockstate - print out the current lockstate
 * @sdp: the filesystem
 * @ub: the buffer to copy the information into
 *
 * If @ub is NULL, dump the lockstate to the console.
 *
 */

static int gfs2_dump_lockstate(struct gfs2_sbd *sdp)
{
        struct gfs2_glock *gl;
        struct hlist_node *h;
        unsigned int x;
        int error = 0;

        for (x = 0; x < GFS2_GL_HASH_SIZE; x++) {

                read_lock(gl_lock_addr(x));

                hlist_for_each_entry(gl, h, &gl_hash_table[x].hb_list, gl_list) {
                        if (gl->gl_sbd != sdp)
                                continue;

                        error = dump_glock(NULL, gl);
                        if (error)
                                break;
                }

                read_unlock(gl_lock_addr(x));

                if (error)
                        break;
        }


        return error;
}


int __init gfs2_glock_init(void)
{
        unsigned i;
        for(i = 0; i < GFS2_GL_HASH_SIZE; i++) {
                INIT_HLIST_HEAD(&gl_hash_table[i].hb_list);
        }
#ifdef GL_HASH_LOCK_SZ
        for(i = 0; i < GL_HASH_LOCK_SZ; i++) {
                rwlock_init(&gl_hash_locks[i]);
        }
#endif

        glock_workqueue = alloc_workqueue("glock_workqueue", WQ_MEM_RECLAIM |
                                          WQ_HIGHPRI | WQ_FREEZABLE, 0);
        if (IS_ERR(glock_workqueue))
                return PTR_ERR(glock_workqueue);
        gfs2_delete_workqueue = alloc_workqueue("delete_workqueue",
                                                WQ_MEM_RECLAIM | WQ_FREEZABLE,
                                                0);
        if (IS_ERR(gfs2_delete_workqueue)) {
                destroy_workqueue(glock_workqueue);
                return PTR_ERR(gfs2_delete_workqueue);
        }

        register_shrinker(&glock_shrinker);

        return 0;
}

void gfs2_glock_exit(void)
{
        unregister_shrinker(&glock_shrinker);
        destroy_workqueue(glock_workqueue);
        destroy_workqueue(gfs2_delete_workqueue);
}

static int gfs2_glock_iter_next(struct gfs2_glock_iter *gi)
{
        struct gfs2_glock *gl;

restart:
        read_lock(gl_lock_addr(gi->hash));
        gl = gi->gl;
        if (gl) {
                gi->gl = hlist_entry(gl->gl_list.next,
                                     struct gfs2_glock, gl_list);
        } else {
                gi->gl = hlist_entry(gl_hash_table[gi->hash].hb_list.first,
                                     struct gfs2_glock, gl_list);
        }
        if (gi->gl)
                gfs2_glock_hold(gi->gl);
        read_unlock(gl_lock_addr(gi->hash));
        if (gl)
                gfs2_glock_put(gl);
        while (gi->gl == NULL) {
                gi->hash++;
                if (gi->hash >= GFS2_GL_HASH_SIZE)
                        return 1;
                read_lock(gl_lock_addr(gi->hash));
                gi->gl = hlist_entry(gl_hash_table[gi->hash].hb_list.first,
                                     struct gfs2_glock, gl_list);
                if (gi->gl)
                        gfs2_glock_hold(gi->gl);
                read_unlock(gl_lock_addr(gi->hash));
        }

        if (gi->sdp != gi->gl->gl_sbd)
                goto restart;

        return 0;
}

static void gfs2_glock_iter_free(struct gfs2_glock_iter *gi)
{
        if (gi->gl)
                gfs2_glock_put(gi->gl);
        gi->gl = NULL;
}

static void *gfs2_glock_seq_start(struct seq_file *seq, loff_t *pos)
{
        struct gfs2_glock_iter *gi = seq->private;
        loff_t n = *pos;

        gi->hash = 0;

        do {
                if (gfs2_glock_iter_next(gi)) {
                        gfs2_glock_iter_free(gi);
                        return NULL;
                }
        } while (n--);

        return gi->gl;
}

static void *gfs2_glock_seq_next(struct seq_file *seq, void *iter_ptr,
                                 loff_t *pos)
{
        struct gfs2_glock_iter *gi = seq->private;

        (*pos)++;

        if (gfs2_glock_iter_next(gi)) {
                gfs2_glock_iter_free(gi);
                return NULL;
        }

        return gi->gl;
}

static void gfs2_glock_seq_stop(struct seq_file *seq, void *iter_ptr)
{
        struct gfs2_glock_iter *gi = seq->private;
        gfs2_glock_iter_free(gi);
}

static int gfs2_glock_seq_show(struct seq_file *seq, void *iter_ptr)
{
        return dump_glock(seq, iter_ptr);
}

static const struct seq_operations gfs2_glock_seq_ops = {
        .start = gfs2_glock_seq_start,
        .next  = gfs2_glock_seq_next,
        .stop  = gfs2_glock_seq_stop,
        .show  = gfs2_glock_seq_show,
};

static int gfs2_debugfs_open(struct inode *inode, struct file *file)
{
        int ret = seq_open_private(file, &gfs2_glock_seq_ops,
                                   sizeof(struct gfs2_glock_iter));
        if (ret == 0) {
                struct seq_file *seq = file->private_data;
                struct gfs2_glock_iter *gi = seq->private;
                gi->sdp = inode->i_private;
        }
        return ret;
}

static const struct file_operations gfs2_debug_fops = {
        .owner   = THIS_MODULE,
        .open    = gfs2_debugfs_open,
        .read    = seq_read,
        .llseek  = seq_lseek,
        .release = seq_release_private,
};

int gfs2_create_debugfs_file(struct gfs2_sbd *sdp)
{
        sdp->debugfs_dir = debugfs_create_dir(sdp->sd_table_name, gfs2_root);
        if (!sdp->debugfs_dir)
                return -ENOMEM;
        sdp->debugfs_dentry_glocks = debugfs_create_file("glocks",
                                                         S_IFREG | S_IRUGO,
                                                         sdp->debugfs_dir, sdp,
                                                         &gfs2_debug_fops);
        if (!sdp->debugfs_dentry_glocks)
                return -ENOMEM;

        return 0;
}

void gfs2_delete_debugfs_file(struct gfs2_sbd *sdp)
{
        if (sdp && sdp->debugfs_dir) {
                if (sdp->debugfs_dentry_glocks) {
                        debugfs_remove(sdp->debugfs_dentry_glocks);
                        sdp->debugfs_dentry_glocks = NULL;
                }
                debugfs_remove(sdp->debugfs_dir);
                sdp->debugfs_dir = NULL;
        }
}

int gfs2_register_debugfs(void)
{
        gfs2_root = debugfs_create_dir("gfs2", NULL);
        return gfs2_root ? 0 : -ENOMEM;
}

void gfs2_unregister_debugfs(void)
{
        debugfs_remove(gfs2_root);
        gfs2_root = NULL;
}