Linux 2.6.28.1

[linux/fpc-iii.git] / fs / ocfs2 / dlm / dlmlock.c

/* -*- mode: c; c-basic-offset: 8; -*-
 * vim: noexpandtab sw=8 ts=8 sts=0:
 *
 * dlmlock.c
 *
 * underlying calls for lock creation
 *
 * 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/slab.h>
#include <linux/highmem.h>
#include <linux/utsname.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/spinlock.h>
#include <linux/delay.h>


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

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

#include "dlmconvert.h"

#define MLOG_MASK_PREFIX ML_DLM
#include "cluster/masklog.h"

static struct kmem_cache *dlm_lock_cache = NULL;

static DEFINE_SPINLOCK(dlm_cookie_lock);
static u64 dlm_next_cookie = 1;

static enum dlm_status dlm_send_remote_lock_request(struct dlm_ctxt *dlm,
                                               struct dlm_lock_resource *res,
                                               struct dlm_lock *lock, int flags);
static void dlm_init_lock(struct dlm_lock *newlock, int type,
                          u8 node, u64 cookie);
static void dlm_lock_release(struct kref *kref);
static void dlm_lock_detach_lockres(struct dlm_lock *lock);

int dlm_init_lock_cache(void)
{
        dlm_lock_cache = kmem_cache_create("o2dlm_lock",
                                           sizeof(struct dlm_lock),
                                           0, SLAB_HWCACHE_ALIGN, NULL);
        if (dlm_lock_cache == NULL)
                return -ENOMEM;
        return 0;
}

void dlm_destroy_lock_cache(void)
{
        if (dlm_lock_cache)
                kmem_cache_destroy(dlm_lock_cache);
}

/* Tell us whether we can grant a new lock request.
 * locking:
 *   caller needs:  res->spinlock
 *   taken:         none
 *   held on exit:  none
 * returns: 1 if the lock can be granted, 0 otherwise.
 */
static int dlm_can_grant_new_lock(struct dlm_lock_resource *res,
                                  struct dlm_lock *lock)
{
        struct list_head *iter;
        struct dlm_lock *tmplock;

        list_for_each(iter, &res->granted) {
                tmplock = list_entry(iter, struct dlm_lock, list);

                if (!dlm_lock_compatible(tmplock->ml.type, lock->ml.type))
                        return 0;
        }

        list_for_each(iter, &res->converting) {
                tmplock = list_entry(iter, struct dlm_lock, list);

                if (!dlm_lock_compatible(tmplock->ml.type, lock->ml.type))
                        return 0;
        }

        return 1;
}

/* performs lock creation at the lockres master site
 * locking:
 *   caller needs:  none
 *   taken:         takes and drops res->spinlock
 *   held on exit:  none
 * returns: DLM_NORMAL, DLM_NOTQUEUED
 */
static enum dlm_status dlmlock_master(struct dlm_ctxt *dlm,
                                      struct dlm_lock_resource *res,
                                      struct dlm_lock *lock, int flags)
{
        int call_ast = 0, kick_thread = 0;
        enum dlm_status status = DLM_NORMAL;

        mlog_entry("type=%d\n", lock->ml.type);

        spin_lock(&res->spinlock);
        /* if called from dlm_create_lock_handler, need to
         * ensure it will not sleep in dlm_wait_on_lockres */
        status = __dlm_lockres_state_to_status(res);
        if (status != DLM_NORMAL &&
            lock->ml.node != dlm->node_num) {
                /* erf.  state changed after lock was dropped. */
                spin_unlock(&res->spinlock);
                dlm_error(status);
                return status;
        }
        __dlm_wait_on_lockres(res);
        __dlm_lockres_reserve_ast(res);

        if (dlm_can_grant_new_lock(res, lock)) {
                mlog(0, "I can grant this lock right away\n");
                /* got it right away */
                lock->lksb->status = DLM_NORMAL;
                status = DLM_NORMAL;
                dlm_lock_get(lock);
                list_add_tail(&lock->list, &res->granted);

                /* for the recovery lock, we can't allow the ast
                 * to be queued since the dlmthread is already
                 * frozen.  but the recovery lock is always locked
                 * with LKM_NOQUEUE so we do not need the ast in
                 * this special case */
                if (!dlm_is_recovery_lock(res->lockname.name,
                                          res->lockname.len)) {
                        kick_thread = 1;
                        call_ast = 1;
                } else {
                        mlog(0, "%s: returning DLM_NORMAL to "
                             "node %u for reco lock\n", dlm->name,
                             lock->ml.node);
                }
        } else {
                /* for NOQUEUE request, unless we get the
                 * lock right away, return DLM_NOTQUEUED */
                if (flags & LKM_NOQUEUE) {
                        status = DLM_NOTQUEUED;
                        if (dlm_is_recovery_lock(res->lockname.name,
                                                 res->lockname.len)) {
                                mlog(0, "%s: returning NOTQUEUED to "
                                     "node %u for reco lock\n", dlm->name,
                                     lock->ml.node);
                        }
                } else {
                        dlm_lock_get(lock);
                        list_add_tail(&lock->list, &res->blocked);
                        kick_thread = 1;
                }
        }
        /* reduce the inflight count, this may result in the lockres
         * being purged below during calc_usage */
        if (lock->ml.node == dlm->node_num)
                dlm_lockres_drop_inflight_ref(dlm, res);

        spin_unlock(&res->spinlock);
        wake_up(&res->wq);

        /* either queue the ast or release it */
        if (call_ast)
                dlm_queue_ast(dlm, lock);
        else
                dlm_lockres_release_ast(dlm, res);

        dlm_lockres_calc_usage(dlm, res);
        if (kick_thread)
                dlm_kick_thread(dlm, res);

        return status;
}

void dlm_revert_pending_lock(struct dlm_lock_resource *res,
                             struct dlm_lock *lock)
{
        /* remove from local queue if it failed */
        list_del_init(&lock->list);
        lock->lksb->flags &= ~DLM_LKSB_GET_LVB;
}


/*
 * locking:
 *   caller needs:  none
 *   taken:         takes and drops res->spinlock
 *   held on exit:  none
 * returns: DLM_DENIED, DLM_RECOVERING, or net status
 */
static enum dlm_status dlmlock_remote(struct dlm_ctxt *dlm,
                                      struct dlm_lock_resource *res,
                                      struct dlm_lock *lock, int flags)
{
        enum dlm_status status = DLM_DENIED;
        int lockres_changed = 1;

        mlog_entry("type=%d\n", lock->ml.type);
        mlog(0, "lockres %.*s, flags = 0x%x\n", res->lockname.len,
             res->lockname.name, flags);

        spin_lock(&res->spinlock);

        /* will exit this call with spinlock held */
        __dlm_wait_on_lockres(res);
        res->state |= DLM_LOCK_RES_IN_PROGRESS;

        /* add lock to local (secondary) queue */
        dlm_lock_get(lock);
        list_add_tail(&lock->list, &res->blocked);
        lock->lock_pending = 1;
        spin_unlock(&res->spinlock);

        /* spec seems to say that you will get DLM_NORMAL when the lock
         * has been queued, meaning we need to wait for a reply here. */
        status = dlm_send_remote_lock_request(dlm, res, lock, flags);

        spin_lock(&res->spinlock);
        res->state &= ~DLM_LOCK_RES_IN_PROGRESS;
        lock->lock_pending = 0;
        if (status != DLM_NORMAL) {
                if (status == DLM_RECOVERING &&
                    dlm_is_recovery_lock(res->lockname.name,
                                         res->lockname.len)) {
                        /* recovery lock was mastered by dead node.
                         * we need to have calc_usage shoot down this
                         * lockres and completely remaster it. */
                        mlog(0, "%s: recovery lock was owned by "
                             "dead node %u, remaster it now.\n",
                             dlm->name, res->owner);
                } else if (status != DLM_NOTQUEUED) {
                        /*
                         * DO NOT call calc_usage, as this would unhash
                         * the remote lockres before we ever get to use
                         * it.  treat as if we never made any change to
                         * the lockres.
                         */
                        lockres_changed = 0;
                        dlm_error(status);
                }
                dlm_revert_pending_lock(res, lock);
                dlm_lock_put(lock);
        } else if (dlm_is_recovery_lock(res->lockname.name, 
                                        res->lockname.len)) {
                /* special case for the $RECOVERY lock.
                 * there will never be an AST delivered to put
                 * this lock on the proper secondary queue
                 * (granted), so do it manually. */
                mlog(0, "%s: $RECOVERY lock for this node (%u) is "
                     "mastered by %u; got lock, manually granting (no ast)\n",
                     dlm->name, dlm->node_num, res->owner);
                list_move_tail(&lock->list, &res->granted);
        }
        spin_unlock(&res->spinlock);

        if (lockres_changed)
                dlm_lockres_calc_usage(dlm, res);

        wake_up(&res->wq);
        return status;
}


/* for remote lock creation.
 * locking:
 *   caller needs:  none, but need res->state & DLM_LOCK_RES_IN_PROGRESS
 *   taken:         none
 *   held on exit:  none
 * returns: DLM_NOLOCKMGR, or net status
 */
static enum dlm_status dlm_send_remote_lock_request(struct dlm_ctxt *dlm,
                                               struct dlm_lock_resource *res,
                                               struct dlm_lock *lock, int flags)
{
        struct dlm_create_lock create;
        int tmpret, status = 0;
        enum dlm_status ret;

        mlog_entry_void();

        memset(&create, 0, sizeof(create));
        create.node_idx = dlm->node_num;
        create.requested_type = lock->ml.type;
        create.cookie = lock->ml.cookie;
        create.namelen = res->lockname.len;
        create.flags = cpu_to_be32(flags);
        memcpy(create.name, res->lockname.name, create.namelen);

        tmpret = o2net_send_message(DLM_CREATE_LOCK_MSG, dlm->key, &create,
                                    sizeof(create), res->owner, &status);
        if (tmpret >= 0) {
                // successfully sent and received
                ret = status;  // this is already a dlm_status
                if (ret == DLM_REJECTED) {
                        mlog(ML_ERROR, "%s:%.*s: BUG.  this is a stale lockres "
                             "no longer owned by %u.  that node is coming back "
                             "up currently.\n", dlm->name, create.namelen,
                             create.name, res->owner);
                        dlm_print_one_lock_resource(res);
                        BUG();
                }
        } else {
                mlog_errno(tmpret);
                if (dlm_is_host_down(tmpret)) {
                        ret = DLM_RECOVERING;
                        mlog(0, "node %u died so returning DLM_RECOVERING "
                             "from lock message!\n", res->owner);
                } else {
                        ret = dlm_err_to_dlm_status(tmpret);
                }
        }

        return ret;
}

void dlm_lock_get(struct dlm_lock *lock)
{
        kref_get(&lock->lock_refs);
}

void dlm_lock_put(struct dlm_lock *lock)
{
        kref_put(&lock->lock_refs, dlm_lock_release);
}

static void dlm_lock_release(struct kref *kref)
{
        struct dlm_lock *lock;

        lock = container_of(kref, struct dlm_lock, lock_refs);

        BUG_ON(!list_empty(&lock->list));
        BUG_ON(!list_empty(&lock->ast_list));
        BUG_ON(!list_empty(&lock->bast_list));
        BUG_ON(lock->ast_pending);
        BUG_ON(lock->bast_pending);

        dlm_lock_detach_lockres(lock);

        if (lock->lksb_kernel_allocated) {
                mlog(0, "freeing kernel-allocated lksb\n");
                kfree(lock->lksb);
        }
        kmem_cache_free(dlm_lock_cache, lock);
}

/* associate a lock with it's lockres, getting a ref on the lockres */
void dlm_lock_attach_lockres(struct dlm_lock *lock,
                             struct dlm_lock_resource *res)
{
        dlm_lockres_get(res);
        lock->lockres = res;
}

/* drop ref on lockres, if there is still one associated with lock */
static void dlm_lock_detach_lockres(struct dlm_lock *lock)
{
        struct dlm_lock_resource *res;

        res = lock->lockres;
        if (res) {
                lock->lockres = NULL;
                mlog(0, "removing lock's lockres reference\n");
                dlm_lockres_put(res);
        }
}

static void dlm_init_lock(struct dlm_lock *newlock, int type,
                          u8 node, u64 cookie)
{
        INIT_LIST_HEAD(&newlock->list);
        INIT_LIST_HEAD(&newlock->ast_list);
        INIT_LIST_HEAD(&newlock->bast_list);
        spin_lock_init(&newlock->spinlock);
        newlock->ml.type = type;
        newlock->ml.convert_type = LKM_IVMODE;
        newlock->ml.highest_blocked = LKM_IVMODE;
        newlock->ml.node = node;
        newlock->ml.pad1 = 0;
        newlock->ml.list = 0;
        newlock->ml.flags = 0;
        newlock->ast = NULL;
        newlock->bast = NULL;
        newlock->astdata = NULL;
        newlock->ml.cookie = cpu_to_be64(cookie);
        newlock->ast_pending = 0;
        newlock->bast_pending = 0;
        newlock->convert_pending = 0;
        newlock->lock_pending = 0;
        newlock->unlock_pending = 0;
        newlock->cancel_pending = 0;
        newlock->lksb_kernel_allocated = 0;

        kref_init(&newlock->lock_refs);
}

struct dlm_lock * dlm_new_lock(int type, u8 node, u64 cookie,
                               struct dlm_lockstatus *lksb)
{
        struct dlm_lock *lock;
        int kernel_allocated = 0;

        lock = (struct dlm_lock *) kmem_cache_zalloc(dlm_lock_cache, GFP_NOFS);
        if (!lock)
                return NULL;

        if (!lksb) {
                /* zero memory only if kernel-allocated */
                lksb = kzalloc(sizeof(*lksb), GFP_NOFS);
                if (!lksb) {
                        kfree(lock);
                        return NULL;
                }
                kernel_allocated = 1;
        }

        dlm_init_lock(lock, type, node, cookie);
        if (kernel_allocated)
                lock->lksb_kernel_allocated = 1;
        lock->lksb = lksb;
        lksb->lockid = lock;
        return lock;
}

/* handler for lock creation net message
 * locking:
 *   caller needs:  none
 *   taken:         takes and drops res->spinlock
 *   held on exit:  none
 * returns: DLM_NORMAL, DLM_SYSERR, DLM_IVLOCKID, DLM_NOTQUEUED
 */
int dlm_create_lock_handler(struct o2net_msg *msg, u32 len, void *data,
                            void **ret_data)
{
        struct dlm_ctxt *dlm = data;
        struct dlm_create_lock *create = (struct dlm_create_lock *)msg->buf;
        struct dlm_lock_resource *res = NULL;
        struct dlm_lock *newlock = NULL;
        struct dlm_lockstatus *lksb = NULL;
        enum dlm_status status = DLM_NORMAL;
        char *name;
        unsigned int namelen;

        BUG_ON(!dlm);

        mlog_entry_void();

        if (!dlm_grab(dlm))
                return DLM_REJECTED;

        name = create->name;
        namelen = create->namelen;
        status = DLM_REJECTED;
        if (!dlm_domain_fully_joined(dlm)) {
                mlog(ML_ERROR, "Domain %s not fully joined, but node %u is "
                     "sending a create_lock message for lock %.*s!\n",
                     dlm->name, create->node_idx, namelen, name);
                dlm_error(status);
                goto leave;
        }

        status = DLM_IVBUFLEN;
        if (namelen > DLM_LOCKID_NAME_MAX) {
                dlm_error(status);
                goto leave;
        }

        status = DLM_SYSERR;
        newlock = dlm_new_lock(create->requested_type,
                               create->node_idx,
                               be64_to_cpu(create->cookie), NULL);
        if (!newlock) {
                dlm_error(status);
                goto leave;
        }

        lksb = newlock->lksb;

        if (be32_to_cpu(create->flags) & LKM_GET_LVB) {
                lksb->flags |= DLM_LKSB_GET_LVB;
                mlog(0, "set DLM_LKSB_GET_LVB flag\n");
        }

        status = DLM_IVLOCKID;
        res = dlm_lookup_lockres(dlm, name, namelen);
        if (!res) {
                dlm_error(status);
                goto leave;
        }

        spin_lock(&res->spinlock);
        status = __dlm_lockres_state_to_status(res);
        spin_unlock(&res->spinlock);

        if (status != DLM_NORMAL) {
                mlog(0, "lockres recovering/migrating/in-progress\n");
                goto leave;
        }

        dlm_lock_attach_lockres(newlock, res);

        status = dlmlock_master(dlm, res, newlock, be32_to_cpu(create->flags));
leave:
        if (status != DLM_NORMAL)
                if (newlock)
                        dlm_lock_put(newlock);

        if (res)
                dlm_lockres_put(res);

        dlm_put(dlm);

        return status;
}


/* fetch next node-local (u8 nodenum + u56 cookie) into u64 */
static inline void dlm_get_next_cookie(u8 node_num, u64 *cookie)
{
        u64 tmpnode = node_num;

        /* shift single byte of node num into top 8 bits */
        tmpnode <<= 56;

        spin_lock(&dlm_cookie_lock);
        *cookie = (dlm_next_cookie | tmpnode);
        if (++dlm_next_cookie & 0xff00000000000000ull) {
                mlog(0, "This node's cookie will now wrap!\n");
                dlm_next_cookie = 1;
        }
        spin_unlock(&dlm_cookie_lock);
}

enum dlm_status dlmlock(struct dlm_ctxt *dlm, int mode,
                        struct dlm_lockstatus *lksb, int flags,
                        const char *name, int namelen, dlm_astlockfunc_t *ast,
                        void *data, dlm_bastlockfunc_t *bast)
{
        enum dlm_status status;
        struct dlm_lock_resource *res = NULL;
        struct dlm_lock *lock = NULL;
        int convert = 0, recovery = 0;

        /* yes this function is a mess.
         * TODO: clean this up.  lots of common code in the
         *       lock and convert paths, especially in the retry blocks */
        if (!lksb) {
                dlm_error(DLM_BADARGS);
                return DLM_BADARGS;
        }

        status = DLM_BADPARAM;
        if (mode != LKM_EXMODE && mode != LKM_PRMODE && mode != LKM_NLMODE) {
                dlm_error(status);
                goto error;
        }

        if (flags & ~LKM_VALID_FLAGS) {
                dlm_error(status);
                goto error;
        }

        convert = (flags & LKM_CONVERT);
        recovery = (flags & LKM_RECOVERY);

        if (recovery &&
            (!dlm_is_recovery_lock(name, namelen) || convert) ) {
                dlm_error(status);
                goto error;
        }
        if (convert && (flags & LKM_LOCAL)) {
                mlog(ML_ERROR, "strange LOCAL convert request!\n");
                goto error;
        }

        if (convert) {
                /* CONVERT request */

                /* if converting, must pass in a valid dlm_lock */
                lock = lksb->lockid;
                if (!lock) {
                        mlog(ML_ERROR, "NULL lock pointer in convert "
                             "request\n");
                        goto error;
                }

                res = lock->lockres;
                if (!res) {
                        mlog(ML_ERROR, "NULL lockres pointer in convert "
                             "request\n");
                        goto error;
                }
                dlm_lockres_get(res);

                /* XXX: for ocfs2 purposes, the ast/bast/astdata/lksb are
                 * static after the original lock call.  convert requests will
                 * ensure that everything is the same, or return DLM_BADARGS.
                 * this means that DLM_DENIED_NOASTS will never be returned.
                 */
                if (lock->lksb != lksb || lock->ast != ast ||
                    lock->bast != bast || lock->astdata != data) {
                        status = DLM_BADARGS;
                        mlog(ML_ERROR, "new args:  lksb=%p, ast=%p, bast=%p, "
                             "astdata=%p\n", lksb, ast, bast, data);
                        mlog(ML_ERROR, "orig args: lksb=%p, ast=%p, bast=%p, "
                             "astdata=%p\n", lock->lksb, lock->ast,
                             lock->bast, lock->astdata);
                        goto error;
                }
retry_convert:
                dlm_wait_for_recovery(dlm);

                if (res->owner == dlm->node_num)
                        status = dlmconvert_master(dlm, res, lock, flags, mode);
                else
                        status = dlmconvert_remote(dlm, res, lock, flags, mode);
                if (status == DLM_RECOVERING || status == DLM_MIGRATING ||
                    status == DLM_FORWARD) {
                        /* for now, see how this works without sleeping
                         * and just retry right away.  I suspect the reco
                         * or migration will complete fast enough that
                         * no waiting will be necessary */
                        mlog(0, "retrying convert with migration/recovery/"
                             "in-progress\n");
                        msleep(100);
                        goto retry_convert;
                }
        } else {
                u64 tmpcookie;

                /* LOCK request */
                status = DLM_BADARGS;
                if (!name) {
                        dlm_error(status);
                        goto error;
                }

                status = DLM_IVBUFLEN;
                if (namelen > DLM_LOCKID_NAME_MAX || namelen < 1) {
                        dlm_error(status);
                        goto error;
                }

                dlm_get_next_cookie(dlm->node_num, &tmpcookie);
                lock = dlm_new_lock(mode, dlm->node_num, tmpcookie, lksb);
                if (!lock) {
                        dlm_error(status);
                        goto error;
                }

                if (!recovery)
                        dlm_wait_for_recovery(dlm);

                /* find or create the lock resource */
                res = dlm_get_lock_resource(dlm, name, namelen, flags);
                if (!res) {
                        status = DLM_IVLOCKID;
                        dlm_error(status);
                        goto error;
                }

                mlog(0, "type=%d, flags = 0x%x\n", mode, flags);
                mlog(0, "creating lock: lock=%p res=%p\n", lock, res);

                dlm_lock_attach_lockres(lock, res);
                lock->ast = ast;
                lock->bast = bast;
                lock->astdata = data;

retry_lock:
                if (flags & LKM_VALBLK) {
                        mlog(0, "LKM_VALBLK passed by caller\n");

                        /* LVB requests for non PR, PW or EX locks are
                         * ignored. */
                        if (mode < LKM_PRMODE)
                                flags &= ~LKM_VALBLK;
                        else {
                                flags |= LKM_GET_LVB;
                                lock->lksb->flags |= DLM_LKSB_GET_LVB;
                        }
                }

                if (res->owner == dlm->node_num)
                        status = dlmlock_master(dlm, res, lock, flags);
                else
                        status = dlmlock_remote(dlm, res, lock, flags);

                if (status == DLM_RECOVERING || status == DLM_MIGRATING ||
                    status == DLM_FORWARD) {
                        mlog(0, "retrying lock with migration/"
                             "recovery/in progress\n");
                        msleep(100);
                        /* no waiting for dlm_reco_thread */
                        if (recovery) {
                                if (status != DLM_RECOVERING)
                                        goto retry_lock;

                                mlog(0, "%s: got RECOVERING "
                                     "for $RECOVERY lock, master "
                                     "was %u\n", dlm->name,
                                     res->owner);
                                /* wait to see the node go down, then
                                 * drop down and allow the lockres to
                                 * get cleaned up.  need to remaster. */
                                dlm_wait_for_node_death(dlm, res->owner,
                                                DLM_NODE_DEATH_WAIT_MAX);
                        } else {
                                dlm_wait_for_recovery(dlm);
                                goto retry_lock;
                        }
                }

                if (status != DLM_NORMAL) {
                        lock->lksb->flags &= ~DLM_LKSB_GET_LVB;
                        if (status != DLM_NOTQUEUED)
                                dlm_error(status);
                        goto error;
                }
        }

error:
        if (status != DLM_NORMAL) {
                if (lock && !convert)
                        dlm_lock_put(lock);
                // this is kind of unnecessary
                lksb->status = status;
        }

        /* put lockres ref from the convert path
         * or from dlm_get_lock_resource */
        if (res)
                dlm_lockres_put(res);

        return status;
}
EXPORT_SYMBOL_GPL(dlmlock);