lustre/osd-ldiskfs/osd_dynlocks.c

   1 /*
   2  * GPL HEADER START
   3  *
   4  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License version 2 only,
   8  * as published by the Free Software Foundation.
   9  *
  10  * This program is distributed in the hope that it will be useful, but
  11  * WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13  * General Public License version 2 for more details (a copy is included
  14  * in the LICENSE file that accompanied this code).
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * version 2 along with this program; If not, see
  18  * http://www.gnu.org/licenses/gpl-2.0.html
  19  *
  20  * GPL HEADER END
  21  *
  22  * Dynamic Locks
  23  *
  24  * struct dynlock is lockspace
  25  * one may request lock (exclusive or shared) for some value
  26  * in that lockspace
  27  *
  28  */
  29
  30 #include <linux/module.h>
  31 #include <linux/slab.h>
  32 #include <linux/sched.h>
  33
  34 #include <libcfs/libcfs.h>
  35
  36 #include <obd_support.h>
  37 #include "osd_dynlocks.h"
  38
  39 extern struct kmem_cache *dynlock_cachep;
  40
  41 #define DYNLOCK_HANDLE_MAGIC    0xd19a10c
  42 #define DYNLOCK_HANDLE_DEAD     0xd1956ee
  43 #define DYNLOCK_LIST_MAGIC      0x11ee91e6
  44
  45 /*
  46  * dynlock_init
  47  *
  48  * initialize lockspace
  49  *
  50  */
  51 void dynlock_init(struct dynlock *dl)
  52 {
  53         spin_lock_init(&dl->dl_list_lock);
  54         INIT_LIST_HEAD(&dl->dl_list);
  55         dl->dl_magic = DYNLOCK_LIST_MAGIC;
  56 }
  57
  58 /*
  59  * dynlock_lock
  60  *
  61  * acquires lock (exclusive or shared) in specified lockspace
  62  * each lock in lockspace is allocated separately, so user have
  63  * to specify GFP flags.
  64  * routine returns pointer to lock. this pointer is intended to
  65  * be passed to dynlock_unlock
  66  *
  67  */
  68 struct dynlock_handle *dynlock_lock(struct dynlock *dl, unsigned long value,
  69                                     enum dynlock_type lt, gfp_t gfp)
  70 {
  71         struct dynlock_handle *nhl = NULL;
  72         struct dynlock_handle *hl;
  73
  74         BUG_ON(dl == NULL);
  75         BUG_ON(dl->dl_magic != DYNLOCK_LIST_MAGIC);
  76
  77 repeat:
  78         /* find requested lock in lockspace */
  79         spin_lock(&dl->dl_list_lock);
  80         BUG_ON(dl->dl_list.next == NULL);
  81         BUG_ON(dl->dl_list.prev == NULL);
  82         list_for_each_entry(hl, &dl->dl_list, dh_list) {
  83                 BUG_ON(hl->dh_list.next == NULL);
  84                 BUG_ON(hl->dh_list.prev == NULL);
  85                 BUG_ON(hl->dh_magic != DYNLOCK_HANDLE_MAGIC);
  86                 if (hl->dh_value == value) {
  87                         /* lock is found */
  88                         if (nhl) {
  89                                 /* someone else just allocated
  90                                  * lock we didn't find and just created
  91                                  * so, we drop our lock
  92                                  */
  93                                 OBD_SLAB_FREE(nhl, dynlock_cachep, sizeof(*nhl));
  94                         }
  95                         hl->dh_refcount++;
  96                         goto found;
  97                 }
  98         }
  99         /* lock not found */
 100         if (nhl) {
 101                 /* we already have allocated lock. use it */
 102                 hl = nhl;
 103                 nhl = NULL;
 104                 list_add(&hl->dh_list, &dl->dl_list);
 105                 goto found;
 106         }
 107         spin_unlock(&dl->dl_list_lock);
 108
 109         /* lock not found and we haven't allocated lock yet. allocate it */
 110         OBD_SLAB_ALLOC_GFP(nhl, dynlock_cachep, sizeof(*nhl), gfp);
 111         if (nhl == NULL)
 112                 return NULL;
 113         nhl->dh_refcount = 1;
 114         nhl->dh_value = value;
 115         nhl->dh_readers = 0;
 116         nhl->dh_writers = 0;
 117         nhl->dh_magic = DYNLOCK_HANDLE_MAGIC;
 118         init_waitqueue_head(&nhl->dh_wait);
 119
 120         /* while lock is being allocated, someone else may allocate it
 121          * and put onto to list. check this situation
 122          */
 123         goto repeat;
 124
 125 found:
 126         if (lt == DLT_WRITE) {
 127                 /* exclusive lock: user don't want to share lock at all
 128                  * NOTE: one process may take the same lock several times
 129                  * this functionaly is useful for rename operations */
 130                 while ((hl->dh_writers && hl->dh_pid != current->pid) ||
 131                                 hl->dh_readers) {
 132                         spin_unlock(&dl->dl_list_lock);
 133                         wait_event(hl->dh_wait,
 134                                 hl->dh_writers == 0 && hl->dh_readers == 0);
 135                         spin_lock(&dl->dl_list_lock);
 136                 }
 137                 hl->dh_writers++;
 138         } else {
 139                 /* shared lock: user do not want to share lock with writer */
 140                 while (hl->dh_writers) {
 141                         spin_unlock(&dl->dl_list_lock);
 142                         wait_event(hl->dh_wait, hl->dh_writers == 0);
 143                         spin_lock(&dl->dl_list_lock);
 144                 }
 145                 hl->dh_readers++;
 146         }
 147         hl->dh_pid = current->pid;
 148         spin_unlock(&dl->dl_list_lock);
 149
 150         return hl;
 151 }
 152
 153 /*
 154  * dynlock_unlock
 155  *
 156  * user have to specify lockspace (dl) and pointer to lock structure
 157  * returned by dynlock_lock()
 158  *
 159  */
 160 void dynlock_unlock(struct dynlock *dl, struct dynlock_handle *hl)
 161 {
 162         int wakeup = 0;
 163
 164         BUG_ON(dl == NULL);
 165         BUG_ON(hl == NULL);
 166         BUG_ON(dl->dl_magic != DYNLOCK_LIST_MAGIC);
 167
 168         if (hl->dh_magic != DYNLOCK_HANDLE_MAGIC)
 169                 printk(KERN_EMERG "wrong lock magic: %#x\n", hl->dh_magic);
 170
 171         BUG_ON(hl->dh_magic != DYNLOCK_HANDLE_MAGIC);
 172         BUG_ON(hl->dh_writers != 0 && current->pid != hl->dh_pid);
 173
 174         spin_lock(&dl->dl_list_lock);
 175         if (hl->dh_writers) {
 176                 BUG_ON(hl->dh_readers != 0);
 177                 hl->dh_writers--;
 178                 if (hl->dh_writers == 0)
 179                         wakeup = 1;
 180         } else if (hl->dh_readers) {
 181                 hl->dh_readers--;
 182                 if (hl->dh_readers == 0)
 183                         wakeup = 1;
 184         } else {
 185                 BUG();
 186         }
 187         if (wakeup) {
 188                 hl->dh_pid = 0;
 189                 wake_up(&hl->dh_wait);
 190         }
 191         if (--(hl->dh_refcount) == 0) {
 192                 hl->dh_magic = DYNLOCK_HANDLE_DEAD;
 193                 list_del(&hl->dh_list);
 194                 OBD_SLAB_FREE(hl, dynlock_cachep, sizeof(*hl));
 195         }
 196         spin_unlock(&dl->dl_list_lock);
 197 }
 198
 199 int dynlock_is_locked(struct dynlock *dl, unsigned long value)
 200 {
 201         struct dynlock_handle *hl;
 202         int result = 0;
 203
 204         /* find requested lock in lockspace */
 205         spin_lock(&dl->dl_list_lock);
 206         BUG_ON(dl->dl_list.next == NULL);
 207         BUG_ON(dl->dl_list.prev == NULL);
 208         list_for_each_entry(hl, &dl->dl_list, dh_list) {
 209                 BUG_ON(hl->dh_list.next == NULL);
 210                 BUG_ON(hl->dh_list.prev == NULL);
 211                 BUG_ON(hl->dh_magic != DYNLOCK_HANDLE_MAGIC);
 212                 if (hl->dh_value == value && hl->dh_pid == current->pid) {
 213                         /* lock is found */
 214                         result = 1;
 215                         break;
 216                 }
 217         }
 218         spin_unlock(&dl->dl_list_lock);
 219         return result;
 220 }