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 #include "osd_internal.h"
  39
  40 #define DYNLOCK_HANDLE_MAGIC    0xd19a10c
  41 #define DYNLOCK_HANDLE_DEAD     0xd1956ee
  42 #define DYNLOCK_LIST_MAGIC      0x11ee91e6
  43
  44 /*
  45  * dynlock_init
  46  *
  47  * initialize lockspace
  48  *
  49  */
  50 void dynlock_init(struct dynlock *dl)
  51 {
  52         spin_lock_init(&dl->dl_list_lock);
  53         INIT_LIST_HEAD(&dl->dl_list);
  54         dl->dl_magic = DYNLOCK_LIST_MAGIC;
  55 }
  56
  57 /*
  58  * dynlock_lock
  59  *
  60  * acquires lock (exclusive or shared) in specified lockspace
  61  * each lock in lockspace is allocated separately, so user have
  62  * to specify GFP flags.
  63  * routine returns pointer to lock. this pointer is intended to
  64  * be passed to dynlock_unlock
  65  *
  66  */
  67 struct dynlock_handle *dynlock_lock(struct dynlock *dl, unsigned long value,
  68                                     enum dynlock_type lt, gfp_t gfp)
  69 {
  70         struct dynlock_handle *nhl = NULL;
  71         struct dynlock_handle *hl;
  72
  73         BUG_ON(dl == NULL);
  74         BUG_ON(dl->dl_magic != DYNLOCK_LIST_MAGIC);
  75
  76 repeat:
  77         /* find requested lock in lockspace */
  78         spin_lock(&dl->dl_list_lock);
  79         BUG_ON(dl->dl_list.next == NULL);
  80         BUG_ON(dl->dl_list.prev == NULL);
  81         list_for_each_entry(hl, &dl->dl_list, dh_list) {
  82                 BUG_ON(hl->dh_list.next == NULL);
  83                 BUG_ON(hl->dh_list.prev == NULL);
  84                 BUG_ON(hl->dh_magic != DYNLOCK_HANDLE_MAGIC);
  85                 if (hl->dh_value == value) {
  86                         /* lock is found */
  87                         if (nhl) {
  88                                 /* someone else just allocated
  89                                  * lock we didn't find and just created
  90                                  * so, we drop our lock
  91                                  */
  92                                 OBD_SLAB_FREE(nhl, dynlock_cachep, sizeof(*nhl));
  93                         }
  94                         hl->dh_refcount++;
  95                         goto found;
  96                 }
  97         }
  98         /* lock not found */
  99         if (nhl) {
 100                 /* we already have allocated lock. use it */
 101                 hl = nhl;
 102                 nhl = NULL;
 103                 list_add(&hl->dh_list, &dl->dl_list);
 104                 goto found;
 105         }
 106         spin_unlock(&dl->dl_list_lock);
 107
 108         /* lock not found and we haven't allocated lock yet. allocate it */
 109         OBD_SLAB_ALLOC_GFP(nhl, dynlock_cachep, sizeof(*nhl), gfp);
 110         if (nhl == NULL)
 111                 return NULL;
 112         nhl->dh_refcount = 1;
 113         nhl->dh_value = value;
 114         nhl->dh_readers = 0;
 115         nhl->dh_writers = 0;
 116         nhl->dh_magic = DYNLOCK_HANDLE_MAGIC;
 117         init_waitqueue_head(&nhl->dh_wait);
 118
 119         /* while lock is being allocated, someone else may allocate it
 120          * and put onto to list. check this situation
 121          */
 122         goto repeat;
 123
 124 found:
 125         if (lt == DLT_WRITE) {
 126                 /* exclusive lock: user don't want to share lock at all
 127                  * NOTE: one process may take the same lock several times
 128                  * this functionaly is useful for rename operations */
 129                 while ((hl->dh_writers && hl->dh_pid != current->pid) ||
 130                                 hl->dh_readers) {
 131                         spin_unlock(&dl->dl_list_lock);
 132                         wait_event(hl->dh_wait,
 133                                 hl->dh_writers == 0 && hl->dh_readers == 0);
 134                         spin_lock(&dl->dl_list_lock);
 135                 }
 136                 hl->dh_writers++;
 137         } else {
 138                 /* shared lock: user do not want to share lock with writer */
 139                 while (hl->dh_writers) {
 140                         spin_unlock(&dl->dl_list_lock);
 141                         wait_event(hl->dh_wait, hl->dh_writers == 0);
 142                         spin_lock(&dl->dl_list_lock);
 143                 }
 144                 hl->dh_readers++;
 145         }
 146         hl->dh_pid = current->pid;
 147         spin_unlock(&dl->dl_list_lock);
 148
 149         return hl;
 150 }
 151
 152 /*
 153  * dynlock_unlock
 154  *
 155  * user have to specify lockspace (dl) and pointer to lock structure
 156  * returned by dynlock_lock()
 157  *
 158  */
 159 void dynlock_unlock(struct dynlock *dl, struct dynlock_handle *hl)
 160 {
 161         int wakeup = 0;
 162
 163         BUG_ON(dl == NULL);
 164         BUG_ON(hl == NULL);
 165         BUG_ON(dl->dl_magic != DYNLOCK_LIST_MAGIC);
 166
 167         if (hl->dh_magic != DYNLOCK_HANDLE_MAGIC)
 168                 printk(KERN_EMERG "wrong lock magic: %#x\n", hl->dh_magic);
 169
 170         BUG_ON(hl->dh_magic != DYNLOCK_HANDLE_MAGIC);
 171         BUG_ON(hl->dh_writers != 0 && current->pid != hl->dh_pid);
 172
 173         spin_lock(&dl->dl_list_lock);
 174         if (hl->dh_writers) {
 175                 BUG_ON(hl->dh_readers != 0);
 176                 hl->dh_writers--;
 177                 if (hl->dh_writers == 0)
 178                         wakeup = 1;
 179         } else if (hl->dh_readers) {
 180                 hl->dh_readers--;
 181                 if (hl->dh_readers == 0)
 182                         wakeup = 1;
 183         } else {
 184                 BUG();
 185         }
 186         if (wakeup) {
 187                 hl->dh_pid = 0;
 188                 wake_up(&hl->dh_wait);
 189         }
 190         if (--(hl->dh_refcount) == 0) {
 191                 hl->dh_magic = DYNLOCK_HANDLE_DEAD;
 192                 list_del(&hl->dh_list);
 193                 OBD_SLAB_FREE(hl, dynlock_cachep, sizeof(*hl));
 194         }
 195         spin_unlock(&dl->dl_list_lock);
 196 }
 197
 198 int dynlock_is_locked(struct dynlock *dl, unsigned long value)
 199 {
 200         struct dynlock_handle *hl;
 201         int result = 0;
 202
 203         /* find requested lock in lockspace */
 204         spin_lock(&dl->dl_list_lock);
 205         BUG_ON(dl->dl_list.next == NULL);
 206         BUG_ON(dl->dl_list.prev == NULL);
 207         list_for_each_entry(hl, &dl->dl_list, dh_list) {
 208                 BUG_ON(hl->dh_list.next == NULL);
 209                 BUG_ON(hl->dh_list.prev == NULL);
 210                 BUG_ON(hl->dh_magic != DYNLOCK_HANDLE_MAGIC);
 211                 if (hl->dh_value == value && hl->dh_pid == current->pid) {
 212                         /* lock is found */
 213                         result = 1;
 214                         break;
 215                 }
 216         }
 217         spin_unlock(&dl->dl_list_lock);
 218         return result;
 219 }