/* -*- mode: c; c-basic-offset: 8; -*-
 * vim: noexpandtab sw=8 ts=8 sts=0:
 *
 * dlmthread.c
 *
 * standalone DLM module
 *
 * Copyright (C) 2004 Oracle.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * 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 for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 *
 */


#include <linux/module.h>
#include <linux/fs.h>
#include <linux/types.h>
#include <linux/highmem.h>
#include <linux/init.h>
#include <linux/sysctl.h>
#include <linux/random.h>
#include <linux/blkdev.h>
#include <linux/socket.h>
#include <linux/inet.h>
#include <linux/timer.h>
#include <linux/kthread.h>
#include <linux/delay.h>


#include "cluster/heartbeat.h"
#include "cluster/nodemanager.h"
#include "cluster/tcp.h"

#include "dlmapi.h"
#include "dlmcommon.h"
#include "dlmdomain.h"

#define MLOG_MASK_PREFIX (ML_DLM|ML_DLM_THREAD)
#include "cluster/masklog.h"

static int dlm_thread(void *data);
static void dlm_flush_asts(struct dlm_ctxt *dlm);

#define dlm_lock_is_remote(dlm, lock)     ((lock)->ml.node != (dlm)->node_num)

/* will exit holding res->spinlock, but may drop in function */
/* waits until flags are cleared on res->state */
void __dlm_wait_on_lockres_flags(struct dlm_lock_resource *res, int flags)
{
        DECLARE_WAITQUEUE(wait, current);

        assert_spin_locked(&res->spinlock);

        add_wait_queue(&res->wq, &wait);
repeat:
        set_current_state(TASK_UNINTERRUPTIBLE);
        if (res->state & flags) {
                spin_unlock(&res->spinlock);
                schedule();
                spin_lock(&res->spinlock);
                goto repeat;
        }
        remove_wait_queue(&res->wq, &wait);
        __set_current_state(TASK_RUNNING);
}

int __dlm_lockres_has_locks(struct dlm_lock_resource *res)
{
        if (list_empty(&res->granted) &&
            list_empty(&res->converting) &&
            list_empty(&res->blocked))
                return 0;
        return 1;
}

/* "unused": the lockres has no locks, is not on the dirty list,
 * has no inflight locks (in the gap between mastery and acquiring
 * the first lock), and has no bits in its refmap.
 * truly ready to be freed. */
int __dlm_lockres_unused(struct dlm_lock_resource *res)
{
        int bit;

        assert_spin_locked(&res->spinlock);

        if (__dlm_lockres_has_locks(res))
                return 0;

        /* Locks are in the process of being created */
        if (res->inflight_locks)
                return 0;

        if (!list_empty(&res->dirty) || res->state & DLM_LOCK_RES_DIRTY)
                return 0;

        if (res->state & (DLM_LOCK_RES_RECOVERING|
                        DLM_LOCK_RES_RECOVERY_WAITING))
                return 0;

        /* Another node has this resource with this node as the master */
        bit = find_next_bit(res->refmap, O2NM_MAX_NODES, 0);
        if (bit < O2NM_MAX_NODES)
                return 0;

        return 1;
}


/* Call whenever you may have added or deleted something from one of
 * the lockres queue's. This will figure out whether it belongs on the
 * unused list or not and does the appropriate thing. */
void __dlm_lockres_calc_usage(struct dlm_ctxt *dlm,
                              struct dlm_lock_resource *res)
{
        assert_spin_locked(&dlm->spinlock);
        assert_spin_locked(&res->spinlock);

        if (__dlm_lockres_unused(res)){
                if (list_empty(&res->purge)) {
                        mlog(0, "%s: Adding res %.*s to purge list\n",
                             dlm->name, res->lockname.len, res->lockname.name);

                        res->last_used = jiffies;
                        dlm_lockres_get(res);
                        list_add_tail(&res->purge, &dlm->purge_list);
                        dlm->purge_count++;
                }
        } else if (!list_empty(&res->purge)) {
                mlog(0, "%s: Removing res %.*s from purge list\n",
                     dlm->name, res->lockname.len, res->lockname.name);

                list_del_init(&res->purge);
                dlm_lockres_put(res);
                dlm->purge_count--;
        }
}

void dlm_lockres_calc_usage(struct dlm_ctxt *dlm,
                            struct dlm_lock_resource *res)
{
        spin_lock(&dlm->spinlock);
        spin_lock(&res->spinlock);

        __dlm_lockres_calc_usage(dlm, res);

        spin_unlock(&res->spinlock);
        spin_unlock(&dlm->spinlock);
}

/*
 * Do the real purge work:
 *     unhash the lockres, and
 *     clear flag DLM_LOCK_RES_DROPPING_REF.
 * It requires dlm and lockres spinlock to be taken.
 */
void __dlm_do_purge_lockres(struct dlm_ctxt *dlm,
                struct dlm_lock_resource *res)
{
        assert_spin_locked(&dlm->spinlock);
        assert_spin_locked(&res->spinlock);

        if (!list_empty(&res->purge)) {
                mlog(0, "%s: Removing res %.*s from purgelist\n",
                     dlm->name, res->lockname.len, res->lockname.name);
                list_del_init(&res->purge);
                dlm_lockres_put(res);
                dlm->purge_count--;
        }

        if (!__dlm_lockres_unused(res)) {
                mlog(ML_ERROR, "%s: res %.*s in use after deref\n",
                     dlm->name, res->lockname.len, res->lockname.name);
                __dlm_print_one_lock_resource(res);
                BUG();
        }

        __dlm_unhash_lockres(dlm, res);

        spin_lock(&dlm->track_lock);
        if (!list_empty(&res->tracking))
                list_del_init(&res->tracking);
        else {
                mlog(ML_ERROR, "%s: Resource %.*s not on the Tracking list\n",
                     dlm->name, res->lockname.len, res->lockname.name);
                __dlm_print_one_lock_resource(res);
        }
        spin_unlock(&dlm->track_lock);

        /*
         * lockres is not in the hash now. drop the flag and wake up
         * any processes waiting in dlm_get_lock_resource.
         */
        res->state &= ~DLM_LOCK_RES_DROPPING_REF;
}

static void dlm_purge_lockres(struct dlm_ctxt *dlm,
                             struct dlm_lock_resource *res)
{
        int master;
        int ret = 0;

        assert_spin_locked(&dlm->spinlock);
        assert_spin_locked(&res->spinlock);

        master = (res->owner == dlm->node_num);

        mlog(0, "%s: Purging res %.*s, master %d\n", dlm->name,
             res->lockname.len, res->lockname.name, master);

        if (!master) {
                if (res->state & DLM_LOCK_RES_DROPPING_REF) {
                        mlog(ML_NOTICE, "%s: res %.*s already in DLM_LOCK_RES_DROPPING_REF state\n",
                                dlm->name, res->lockname.len, res->lockname.name);
                        spin_unlock(&res->spinlock);
                        return;
                }

                res->state |= DLM_LOCK_RES_DROPPING_REF;
                /* drop spinlock...  retake below */
                spin_unlock(&res->spinlock);
                spin_unlock(&dlm->spinlock);

                spin_lock(&res->spinlock);
                /* This ensures that clear refmap is sent after the set */
                __dlm_wait_on_lockres_flags(res, DLM_LOCK_RES_SETREF_INPROG);
                spin_unlock(&res->spinlock);

                /* clear our bit from the master's refmap, ignore errors */
                ret = dlm_drop_lockres_ref(dlm, res);
                if (ret < 0) {
                        if (!dlm_is_host_down(ret))
                                BUG();
                }
                spin_lock(&dlm->spinlock);
                spin_lock(&res->spinlock);
        }

        if (!list_empty(&res->purge)) {
                mlog(0, "%s: Removing res %.*s from purgelist, master %d\n",
                     dlm->name, res->lockname.len, res->lockname.name, master);
                list_del_init(&res->purge);
                dlm_lockres_put(res);
                dlm->purge_count--;
        }

        if (!master && ret == DLM_DEREF_RESPONSE_INPROG) {
                mlog(0, "%s: deref %.*s in progress\n",
                        dlm->name, res->lockname.len, res->lockname.name);
                spin_unlock(&res->spinlock);
                return;
        }

        if (!__dlm_lockres_unused(res)) {
                mlog(ML_ERROR, "%s: res %.*s in use after deref\n",
                     dlm->name, res->lockname.len, res->lockname.name);
                __dlm_print_one_lock_resource(res);
                BUG();
        }

        __dlm_unhash_lockres(dlm, res);

        spin_lock(&dlm->track_lock);
        if (!list_empty(&res->tracking))
                list_del_init(&res->tracking);
        else {
                mlog(ML_ERROR, "Resource %.*s not on the Tracking list\n",
                                res->lockname.len, res->lockname.name);
                __dlm_print_one_lock_resource(res);
        }
        spin_unlock(&dlm->track_lock);

        /* lockres is not in the hash now.  drop the flag and wake up
         * any processes waiting in dlm_get_lock_resource. */
        if (!master) {
                res->state &= ~DLM_LOCK_RES_DROPPING_REF;
                spin_unlock(&res->spinlock);
                wake_up(&res->wq);
        } else
                spin_unlock(&res->spinlock);
}

static void dlm_run_purge_list(struct dlm_ctxt *dlm,
                               int purge_now)
{
        unsigned int run_max, unused;
        unsigned long purge_jiffies;
        struct dlm_lock_resource *lockres;

        spin_lock(&dlm->spinlock);
        run_max = dlm->purge_count;

        while(run_max && !list_empty(&dlm->purge_list)) {
                run_max--;

                lockres = list_entry(dlm->purge_list.next,
                                     struct dlm_lock_resource, purge);

                spin_lock(&lockres->spinlock);

                purge_jiffies = lockres->last_used +
                        msecs_to_jiffies(DLM_PURGE_INTERVAL_MS);

                /* Make sure that we want to be processing this guy at
                 * this time. */
                if (!purge_now && time_after(purge_jiffies, jiffies)) {
                        /* Since resources are added to the purge list
                         * in tail order, we can stop at the first
                         * unpurgable resource -- anyone added after
                         * him will have a greater last_used value */
                        spin_unlock(&lockres->spinlock);
                        break;
                }

                /* Status of the lockres *might* change so double
                 * check. If the lockres is unused, holding the dlm
                 * spinlock will prevent people from getting and more
                 * refs on it. */
                unused = __dlm_lockres_unused(lockres);
                if (!unused ||
                    (lockres->state & DLM_LOCK_RES_MIGRATING) ||
                    (lockres->inflight_assert_workers != 0)) {
                        mlog(0, "%s: res %.*s is in use or being remastered, "
                             "used %d, state %d, assert master workers %u\n",
                             dlm->name, lockres->lockname.len,
                             lockres->lockname.name,
                             !unused, lockres->state,
                             lockres->inflight_assert_workers);
                        list_move_tail(&lockres->purge, &dlm->purge_list);
                        spin_unlock(&lockres->spinlock);
                        continue;
                }

                dlm_lockres_get(lockres);

                dlm_purge_lockres(dlm, lockres);

                dlm_lockres_put(lockres);

                /* Avoid adding any scheduling latencies */
                cond_resched_lock(&dlm->spinlock);
        }

        spin_unlock(&dlm->spinlock);
}

static void dlm_shuffle_lists(struct dlm_ctxt *dlm,
                              struct dlm_lock_resource *res)
{
        struct dlm_lock *lock, *target;
        int can_grant = 1;

        /*
         * Because this function is called with the lockres
         * spinlock, and because we know that it is not migrating/
         * recovering/in-progress, it is fine to reserve asts and
         * basts right before queueing them all throughout
         */
        assert_spin_locked(&dlm->ast_lock);
        assert_spin_locked(&res->spinlock);
        BUG_ON((res->state & (DLM_LOCK_RES_MIGRATING|
                              DLM_LOCK_RES_RECOVERING|
                              DLM_LOCK_RES_IN_PROGRESS)));

converting:
        if (list_empty(&res->converting))
                goto blocked;
        mlog(0, "%s: res %.*s has locks on the convert queue\n", dlm->name,
             res->lockname.len, res->lockname.name);

        target = list_entry(res->converting.next, struct dlm_lock, list);
        if (target->ml.convert_type == LKM_IVMODE) {
                mlog(ML_ERROR, "%s: res %.*s converting lock to invalid mode\n",
                     dlm->name, res->lockname.len, res->lockname.name);
                BUG();
        }
        list_for_each_entry(lock, &res->granted, list) {
                if (lock==target)
                        continue;
                if (!dlm_lock_compatible(lock->ml.type,
                                         target->ml.convert_type)) {
                        can_grant = 0;
                        /* queue the BAST if not already */
                        if (lock->ml.highest_blocked == LKM_IVMODE) {
                                __dlm_lockres_reserve_ast(res);
                                __dlm_queue_bast(dlm, lock);
                        }
                        /* update the highest_blocked if needed */
                        if (lock->ml.highest_blocked < target->ml.convert_type)
                                lock->ml.highest_blocked =
                                        target->ml.convert_type;
                }
        }

        list_for_each_entry(lock, &res->converting, list) {
                if (lock==target)
                        continue;
                if (!dlm_lock_compatible(lock->ml.type,
                                         target->ml.convert_type)) {
                        can_grant = 0;
                        if (lock->ml.highest_blocked == LKM_IVMODE) {
                                __dlm_lockres_reserve_ast(res);
                                __dlm_queue_bast(dlm, lock);
                        }
                        if (lock->ml.highest_blocked < target->ml.convert_type)
                                lock->ml.highest_blocked =
                                        target->ml.convert_type;
                }
        }

        /* we can convert the lock */
        if (can_grant) {
                spin_lock(&target->spinlock);
                BUG_ON(target->ml.highest_blocked != LKM_IVMODE);

                mlog(0, "%s: res %.*s, AST for Converting lock %u:%llu, type "
                     "%d => %d, node %u\n", dlm->name, res->lockname.len,
                     res->lockname.name,
                     dlm_get_lock_cookie_node(be64_to_cpu(target->ml.cookie)),
                     dlm_get_lock_cookie_seq(be64_to_cpu(target->ml.cookie)),
                     target->ml.type,
                     target->ml.convert_type, target->ml.node);

                target->ml.type = target->ml.convert_type;
                target->ml.convert_type = LKM_IVMODE;
                list_move_tail(&target->list, &res->granted);

                BUG_ON(!target->lksb);
                target->lksb->status = DLM_NORMAL;

                spin_unlock(&target->spinlock);

                __dlm_lockres_reserve_ast(res);
                __dlm_queue_ast(dlm, target);
                /* go back and check for more */
                goto converting;
        }

blocked:
        if (list_empty(&res->blocked))
                goto leave;
        target = list_entry(res->blocked.next, struct dlm_lock, list);

        list_for_each_entry(lock, &res->granted, list) {
                if (lock==target)
                        continue;
                if (!dlm_lock_compatible(lock->ml.type, target->ml.type)) {
                        can_grant = 0;
                        if (lock->ml.highest_blocked == LKM_IVMODE) {
                                __dlm_lockres_reserve_ast(res);
                                __dlm_queue_bast(dlm, lock);
                        }
                        if (lock->ml.highest_blocked < target->ml.type)
                                lock->ml.highest_blocked = target->ml.type;
                }
        }

        list_for_each_entry(lock, &res->converting, list) {
                if (lock==target)
                        continue;
                if (!dlm_lock_compatible(lock->ml.type, target->ml.type)) {
                        can_grant = 0;
                        if (lock->ml.highest_blocked == LKM_IVMODE) {
                                __dlm_lockres_reserve_ast(res);
                                __dlm_queue_bast(dlm, lock);
                        }
                        if (lock->ml.highest_blocked < target->ml.type)
                                lock->ml.highest_blocked = target->ml.type;
                }
        }

        /* we can grant the blocked lock (only
         * possible if converting list empty) */
        if (can_grant) {
                spin_lock(&target->spinlock);
                BUG_ON(target->ml.highest_blocked != LKM_IVMODE);

                mlog(0, "%s: res %.*s, AST for Blocked lock %u:%llu, type %d, "
                     "node %u\n", dlm->name, res->lockname.len,
                     res->lockname.name,
                     dlm_get_lock_cookie_node(be64_to_cpu(target->ml.cookie)),
                     dlm_get_lock_cookie_seq(be64_to_cpu(target->ml.cookie)),
                     target->ml.type, target->ml.node);

                /* target->ml.type is already correct */
                list_move_tail(&target->list, &res->granted);

                BUG_ON(!target->lksb);
                target->lksb->status = DLM_NORMAL;

                spin_unlock(&target->spinlock);

                __dlm_lockres_reserve_ast(res);
                __dlm_queue_ast(dlm, target);
                /* go back and check for more */
                goto converting;
        }

leave:
        return;
}

/* must have NO locks when calling this with res !=NULL * */
void dlm_kick_thread(struct dlm_ctxt *dlm, struct dlm_lock_resource *res)
{
        if (res) {
                spin_lock(&dlm->spinlock);
                spin_lock(&res->spinlock);
                __dlm_dirty_lockres(dlm, res);
                spin_unlock(&res->spinlock);
                spin_unlock(&dlm->spinlock);
        }
        wake_up(&dlm->dlm_thread_wq);
}

void __dlm_dirty_lockres(struct dlm_ctxt *dlm, struct dlm_lock_resource *res)
{
        assert_spin_locked(&dlm->spinlock);
        assert_spin_locked(&res->spinlock);

        /* don't shuffle secondary queues */
        if (res->owner == dlm->node_num) {
                if (res->state & (DLM_LOCK_RES_MIGRATING |
                                  DLM_LOCK_RES_BLOCK_DIRTY))
                    return;

                if (list_empty(&res->dirty)) {
                        /* ref for dirty_list */
                        dlm_lockres_get(res);
                        list_add_tail(&res->dirty, &dlm->dirty_list);
                        res->state |= DLM_LOCK_RES_DIRTY;
                }
        }

        mlog(0, "%s: res %.*s\n", dlm->name, res->lockname.len,
             res->lockname.name);
}


/* Launch the NM thread for the mounted volume */
int dlm_launch_thread(struct dlm_ctxt *dlm)
{
        mlog(0, "Starting dlm_thread...\n");

        dlm->dlm_thread_task = kthread_run(dlm_thread, dlm, "dlm-%s",
                        dlm->name);
        if (IS_ERR(dlm->dlm_thread_task)) {
                mlog_errno(PTR_ERR(dlm->dlm_thread_task));
                dlm->dlm_thread_task = NULL;
                return -EINVAL;
        }

        return 0;
}

void dlm_complete_thread(struct dlm_ctxt *dlm)
{
        if (dlm->dlm_thread_task) {
                mlog(ML_KTHREAD, "Waiting for dlm thread to exit\n");
                kthread_stop(dlm->dlm_thread_task);
                dlm->dlm_thread_task = NULL;
        }
}

static int dlm_dirty_list_empty(struct dlm_ctxt *dlm)
{
        int empty;

        spin_lock(&dlm->spinlock);
        empty = list_empty(&dlm->dirty_list);
        spin_unlock(&dlm->spinlock);

        return empty;
}

static void dlm_flush_asts(struct dlm_ctxt *dlm)
{
        int ret;
        struct dlm_lock *lock;
        struct dlm_lock_resource *res;
        u8 hi;

        spin_lock(&dlm->ast_lock);
        while (!list_empty(&dlm->pending_asts)) {
                lock = list_entry(dlm->pending_asts.next,
                                  struct dlm_lock, ast_list);
                /* get an extra ref on lock */
                dlm_lock_get(lock);
                res = lock->lockres;
                mlog(0, "%s: res %.*s, Flush AST for lock %u:%llu, type %d, "
                     "node %u\n", dlm->name, res->lockname.len,
                     res->lockname.name,
                     dlm_get_lock_cookie_node(be64_to_cpu(lock->ml.cookie)),
                     dlm_get_lock_cookie_seq(be64_to_cpu(lock->ml.cookie)),
                     lock->ml.type, lock->ml.node);

                BUG_ON(!lock->ast_pending);

                /* remove from list (including ref) */
                list_del_init(&lock->ast_list);
                dlm_lock_put(lock);
                spin_unlock(&dlm->ast_lock);

                if (lock->ml.node != dlm->node_num) {
                        ret = dlm_do_remote_ast(dlm, res, lock);
                        if (ret < 0)
                                mlog_errno(ret);
                } else
                        dlm_do_local_ast(dlm, res, lock);

                spin_lock(&dlm->ast_lock);

                /* possible that another ast was queued while
                 * we were delivering the last one */
                if (!list_empty(&lock->ast_list)) {
                        mlog(0, "%s: res %.*s, AST queued while flushing last "
                             "one\n", dlm->name, res->lockname.len,
                             res->lockname.name);
                } else
                        lock->ast_pending = 0;

                /* drop the extra ref.
                 * this may drop it completely. */
                dlm_lock_put(lock);
                dlm_lockres_release_ast(dlm, res);
        }

        while (!list_empty(&dlm->pending_basts)) {
                lock = list_entry(dlm->pending_basts.next,
                                  struct dlm_lock, bast_list);
                /* get an extra ref on lock */
                dlm_lock_get(lock);
                res = lock->lockres;

                BUG_ON(!lock->bast_pending);

                /* get the highest blocked lock, and reset */
                spin_lock(&lock->spinlock);
                BUG_ON(lock->ml.highest_blocked <= LKM_IVMODE);
                hi = lock->ml.highest_blocked;
                lock->ml.highest_blocked = LKM_IVMODE;
                spin_unlock(&lock->spinlock);

                /* remove from list (including ref) */
                list_del_init(&lock->bast_list);
                dlm_lock_put(lock);
                spin_unlock(&dlm->ast_lock);

                mlog(0, "%s: res %.*s, Flush BAST for lock %u:%llu, "
                     "blocked %d, node %u\n",
                     dlm->name, res->lockname.len, res->lockname.name,
                     dlm_get_lock_cookie_node(be64_to_cpu(lock->ml.cookie)),
                     dlm_get_lock_cookie_seq(be64_to_cpu(lock->ml.cookie)),
                     hi, lock->ml.node);

                if (lock->ml.node != dlm->node_num) {
                        ret = dlm_send_proxy_bast(dlm, res, lock, hi);
                        if (ret < 0)
                                mlog_errno(ret);
                } else
                        dlm_do_local_bast(dlm, res, lock, hi);

                spin_lock(&dlm->ast_lock);

                /* possible that another bast was queued while
                 * we were delivering the last one */
                if (!list_empty(&lock->bast_list)) {
                        mlog(0, "%s: res %.*s, BAST queued while flushing last "
                             "one\n", dlm->name, res->lockname.len,
                             res->lockname.name);
                } else
                        lock->bast_pending = 0;

                /* drop the extra ref.
                 * this may drop it completely. */
                dlm_lock_put(lock);
                dlm_lockres_release_ast(dlm, res);
        }
        wake_up(&dlm->ast_wq);
        spin_unlock(&dlm->ast_lock);
}


#define DLM_THREAD_TIMEOUT_MS (4 * 1000)
#define DLM_THREAD_MAX_DIRTY  100
#define DLM_THREAD_MAX_ASTS   10

static int dlm_thread(void *data)
{
        struct dlm_lock_resource *res;
        struct dlm_ctxt *dlm = data;
        unsigned long timeout = msecs_to_jiffies(DLM_THREAD_TIMEOUT_MS);

        mlog(0, "dlm thread running for %s...\n", dlm->name);

        while (!kthread_should_stop()) {
                int n = DLM_THREAD_MAX_DIRTY;

                /* dlm_shutting_down is very point-in-time, but that
                 * doesn't matter as we'll just loop back around if we
                 * get false on the leading edge of a state
                 * transition. */
                dlm_run_purge_list(dlm, dlm_shutting_down(dlm));

                /* We really don't want to hold dlm->spinlock while
                 * calling dlm_shuffle_lists on each lockres that
                 * needs to have its queues adjusted and AST/BASTs
                 * run.  So let's pull each entry off the dirty_list
                 * and drop dlm->spinlock ASAP.  Once off the list,
                 * res->spinlock needs to be taken again to protect
                 * the queues while calling dlm_shuffle_lists.  */
                spin_lock(&dlm->spinlock);
                while (!list_empty(&dlm->dirty_list)) {
                        int delay = 0;
                        res = list_entry(dlm->dirty_list.next,
                                         struct dlm_lock_resource, dirty);

                        /* peel a lockres off, remove it from the list,
                         * unset the dirty flag and drop the dlm lock */
                        BUG_ON(!res);
                        dlm_lockres_get(res);

                        spin_lock(&res->spinlock);
                        /* We clear the DLM_LOCK_RES_DIRTY state once we shuffle lists below */
                        list_del_init(&res->dirty);
                        spin_unlock(&res->spinlock);
                        spin_unlock(&dlm->spinlock);
                        /* Drop dirty_list ref */
                        dlm_lockres_put(res);

                        /* lockres can be re-dirtied/re-added to the
                         * dirty_list in this gap, but that is ok */

                        spin_lock(&dlm->ast_lock);
                        spin_lock(&res->spinlock);
                        if (res->owner != dlm->node_num) {
                                __dlm_print_one_lock_resource(res);
                                mlog(ML_ERROR, "%s: inprog %d, mig %d, reco %d,"
                                     " dirty %d\n", dlm->name,
                                     !!(res->state & DLM_LOCK_RES_IN_PROGRESS),
                                     !!(res->state & DLM_LOCK_RES_MIGRATING),
                                     !!(res->state & DLM_LOCK_RES_RECOVERING),
                                     !!(res->state & DLM_LOCK_RES_DIRTY));
                        }
                        BUG_ON(res->owner != dlm->node_num);

                        /* it is now ok to move lockreses in these states
                         * to the dirty list, assuming that they will only be
                         * dirty for a short while. */
                        BUG_ON(res->state & DLM_LOCK_RES_MIGRATING);
                        if (res->state & (DLM_LOCK_RES_IN_PROGRESS |
                                          DLM_LOCK_RES_RECOVERING |
                                          DLM_LOCK_RES_RECOVERY_WAITING)) {
                                /* move it to the tail and keep going */
                                res->state &= ~DLM_LOCK_RES_DIRTY;
                                spin_unlock(&res->spinlock);
                                spin_unlock(&dlm->ast_lock);
                                mlog(0, "%s: res %.*s, inprogress, delay list "
                                     "shuffle, state %d\n", dlm->name,
                                     res->lockname.len, res->lockname.name,
                                     res->state);
                                delay = 1;
                                goto in_progress;
                        }

                        /* at this point the lockres is not migrating/
                         * recovering/in-progress.  we have the lockres
                         * spinlock and do NOT have the dlm lock.
                         * safe to reserve/queue asts and run the lists. */

                        /* called while holding lockres lock */
                        dlm_shuffle_lists(dlm, res);
                        res->state &= ~DLM_LOCK_RES_DIRTY;
                        spin_unlock(&res->spinlock);
                        spin_unlock(&dlm->ast_lock);

                        dlm_lockres_calc_usage(dlm, res);

in_progress:

                        spin_lock(&dlm->spinlock);
                        /* if the lock was in-progress, stick
                         * it on the back of the list */
                        if (delay) {
                                spin_lock(&res->spinlock);
                                __dlm_dirty_lockres(dlm, res);
                                spin_unlock(&res->spinlock);
                        }
                        dlm_lockres_put(res);

                        /* unlikely, but we may need to give time to
                         * other tasks */
                        if (!--n) {
                                mlog(0, "%s: Throttling dlm thread\n",
                                     dlm->name);
                                break;
                        }
                }

                spin_unlock(&dlm->spinlock);
                dlm_flush_asts(dlm);

                /* yield and continue right away if there is more work to do */
                if (!n) {
                        cond_resched();
                        continue;
                }

                wait_event_interruptible_timeout(dlm->dlm_thread_wq,
                                                 !dlm_dirty_list_empty(dlm) ||
                                                 kthread_should_stop(),
                                                 timeout);
        }

        mlog(0, "quitting DLM thread\n");
        return 0;
}