fs/ocfs2/cluster/quorum.c

   1 /* -*- mode: c; c-basic-offset: 8; -*-
   2  *
   3  * vim: noexpandtab sw=8 ts=8 sts=0:
   4  *
   5  * Copyright (C) 2005 Oracle.  All rights reserved.
   6  *
   7  * This program is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2 of the License, or (at your option) any later version.
  11  *
  12  * This program is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU General Public
  18  * License along with this program; if not, write to the
  19  * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  20  * Boston, MA 021110-1307, USA.
  21  */
  22
  23 /* This quorum hack is only here until we transition to some more rational
  24  * approach that is driven from userspace.  Honest.  No foolin'.
  25  *
  26  * Imagine two nodes lose network connectivity to each other but they're still
  27  * up and operating in every other way.  Presumably a network timeout indicates
  28  * that a node is broken and should be recovered.  They can't both recover each
  29  * other and both carry on without serialising their access to the file system.
  30  * They need to decide who is authoritative.  Now extend that problem to
  31  * arbitrary groups of nodes losing connectivity between each other.
  32  *
  33  * So we declare that a node which has given up on connecting to a majority
  34  * of nodes who are still heartbeating will fence itself.
  35  *
  36  * There are huge opportunities for races here.  After we give up on a node's
  37  * connection we need to wait long enough to give heartbeat an opportunity
  38  * to declare the node as truly dead.  We also need to be careful with the
  39  * race between when we see a node start heartbeating and when we connect
  40  * to it.
  41  *
  42  * So nodes that are in this transtion put a hold on the quorum decision
  43  * with a counter.  As they fall out of this transition they drop the count
  44  * and if they're the last, they fire off the decision.
  45  */
  46 #include <linux/kernel.h>
  47 #include <linux/slab.h>
  48 #include <linux/workqueue.h>
  49 #include <linux/reboot.h>
  50
  51 #include "heartbeat.h"
  52 #include "nodemanager.h"
  53 #define MLOG_MASK_PREFIX ML_QUORUM
  54 #include "masklog.h"
  55 #include "quorum.h"
  56
  57 static struct o2quo_state {
  58         spinlock_t              qs_lock;
  59         struct work_struct      qs_work;
  60         int                     qs_pending;
  61         int                     qs_heartbeating;
  62         unsigned long           qs_hb_bm[BITS_TO_LONGS(O2NM_MAX_NODES)];
  63         int                     qs_connected;
  64         unsigned long           qs_conn_bm[BITS_TO_LONGS(O2NM_MAX_NODES)];
  65         int                     qs_holds;
  66         unsigned long           qs_hold_bm[BITS_TO_LONGS(O2NM_MAX_NODES)];
  67 } o2quo_state;
  68
  69 /* this is horribly heavy-handed.  It should instead flip the file
  70  * system RO and call some userspace script. */
  71 static void o2quo_fence_self(void)
  72 {
  73         /* panic spins with interrupts enabled.  with preempt
  74          * threads can still schedule, etc, etc */
  75         o2hb_stop_all_regions();
  76
  77         printk("ocfs2 is very sorry to be fencing this system by restarting\n");
  78         emergency_restart();
  79 }
  80
  81 /* Indicate that a timeout occured on a hearbeat region write. The
  82  * other nodes in the cluster may consider us dead at that time so we
  83  * want to "fence" ourselves so that we don't scribble on the disk
  84  * after they think they've recovered us. This can't solve all
  85  * problems related to writeout after recovery but this hack can at
  86  * least close some of those gaps. When we have real fencing, this can
  87  * go away as our node would be fenced externally before other nodes
  88  * begin recovery. */
  89 void o2quo_disk_timeout(void)
  90 {
  91         o2quo_fence_self();
  92 }
  93
  94 static void o2quo_make_decision(struct work_struct *work)
  95 {
  96         int quorum;
  97         int lowest_hb, lowest_reachable = 0, fence = 0;
  98         struct o2quo_state *qs = &o2quo_state;
  99
 100         spin_lock(&qs->qs_lock);
 101
 102         lowest_hb = find_first_bit(qs->qs_hb_bm, O2NM_MAX_NODES);
 103         if (lowest_hb != O2NM_MAX_NODES)
 104                 lowest_reachable = test_bit(lowest_hb, qs->qs_conn_bm);
 105
 106         mlog(0, "heartbeating: %d, connected: %d, "
 107              "lowest: %d (%sreachable)\n", qs->qs_heartbeating,
 108              qs->qs_connected, lowest_hb, lowest_reachable ? "" : "un");
 109
 110         if (!test_bit(o2nm_this_node(), qs->qs_hb_bm) ||
 111             qs->qs_heartbeating == 1)
 112                 goto out;
 113
 114         if (qs->qs_heartbeating & 1) {
 115                 /* the odd numbered cluster case is straight forward --
 116                  * if we can't talk to the majority we're hosed */
 117                 quorum = (qs->qs_heartbeating + 1)/2;
 118                 if (qs->qs_connected < quorum) {
 119                         mlog(ML_ERROR, "fencing this node because it is "
 120                              "only connected to %u nodes and %u is needed "
 121                              "to make a quorum out of %u heartbeating nodes\n",
 122                              qs->qs_connected, quorum,
 123                              qs->qs_heartbeating);
 124                         fence = 1;
 125                 }
 126         } else {
 127                 /* the even numbered cluster adds the possibility of each half
 128                  * of the cluster being able to talk amongst themselves.. in
 129                  * that case we're hosed if we can't talk to the group that has
 130                  * the lowest numbered node */
 131                 quorum = qs->qs_heartbeating / 2;
 132                 if (qs->qs_connected < quorum) {
 133                         mlog(ML_ERROR, "fencing this node because it is "
 134                              "only connected to %u nodes and %u is needed "
 135                              "to make a quorum out of %u heartbeating nodes\n",
 136                              qs->qs_connected, quorum,
 137                              qs->qs_heartbeating);
 138                         fence = 1;
 139                 }
 140                 else if ((qs->qs_connected == quorum) &&
 141                          !lowest_reachable) {
 142                         mlog(ML_ERROR, "fencing this node because it is "
 143                              "connected to a half-quorum of %u out of %u "
 144                              "nodes which doesn't include the lowest active "
 145                              "node %u\n", quorum, qs->qs_heartbeating,
 146                              lowest_hb);
 147                         fence = 1;
 148                 }
 149         }
 150
 151 out:
 152         spin_unlock(&qs->qs_lock);
 153         if (fence)
 154                 o2quo_fence_self();
 155 }
 156
 157 static void o2quo_set_hold(struct o2quo_state *qs, u8 node)
 158 {
 159         assert_spin_locked(&qs->qs_lock);
 160
 161         if (!test_and_set_bit(node, qs->qs_hold_bm)) {
 162                 qs->qs_holds++;
 163                 mlog_bug_on_msg(qs->qs_holds == O2NM_MAX_NODES,
 164                                 "node %u\n", node);
 165                 mlog(0, "node %u, %d total\n", node, qs->qs_holds);
 166         }
 167 }
 168
 169 static void o2quo_clear_hold(struct o2quo_state *qs, u8 node)
 170 {
 171         assert_spin_locked(&qs->qs_lock);
 172
 173         if (test_and_clear_bit(node, qs->qs_hold_bm)) {
 174                 mlog(0, "node %u, %d total\n", node, qs->qs_holds - 1);
 175                 if (--qs->qs_holds == 0) {
 176                         if (qs->qs_pending) {
 177                                 qs->qs_pending = 0;
 178                                 schedule_work(&qs->qs_work);
 179                         }
 180                 }
 181                 mlog_bug_on_msg(qs->qs_holds < 0, "node %u, holds %d\n",
 182                                 node, qs->qs_holds);
 183         }
 184 }
 185
 186 /* as a node comes up we delay the quorum decision until we know the fate of
 187  * the connection.  the hold will be droped in conn_up or hb_down.  it might be
 188  * perpetuated by con_err until hb_down.  if we already have a conn, we might
 189  * be dropping a hold that conn_up got. */
 190 void o2quo_hb_up(u8 node)
 191 {
 192         struct o2quo_state *qs = &o2quo_state;
 193
 194         spin_lock(&qs->qs_lock);
 195
 196         qs->qs_heartbeating++;
 197         mlog_bug_on_msg(qs->qs_heartbeating == O2NM_MAX_NODES,
 198                         "node %u\n", node);
 199         mlog_bug_on_msg(test_bit(node, qs->qs_hb_bm), "node %u\n", node);
 200         set_bit(node, qs->qs_hb_bm);
 201
 202         mlog(0, "node %u, %d total\n", node, qs->qs_heartbeating);
 203
 204         if (!test_bit(node, qs->qs_conn_bm))
 205                 o2quo_set_hold(qs, node);
 206         else
 207                 o2quo_clear_hold(qs, node);
 208
 209         spin_unlock(&qs->qs_lock);
 210 }
 211
 212 /* hb going down releases any holds we might have had due to this node from
 213  * conn_up, conn_err, or hb_up */
 214 void o2quo_hb_down(u8 node)
 215 {
 216         struct o2quo_state *qs = &o2quo_state;
 217
 218         spin_lock(&qs->qs_lock);
 219
 220         qs->qs_heartbeating--;
 221         mlog_bug_on_msg(qs->qs_heartbeating < 0,
 222                         "node %u, %d heartbeating\n",
 223                         node, qs->qs_heartbeating);
 224         mlog_bug_on_msg(!test_bit(node, qs->qs_hb_bm), "node %u\n", node);
 225         clear_bit(node, qs->qs_hb_bm);
 226
 227         mlog(0, "node %u, %d total\n", node, qs->qs_heartbeating);
 228
 229         o2quo_clear_hold(qs, node);
 230
 231         spin_unlock(&qs->qs_lock);
 232 }
 233
 234 /* this tells us that we've decided that the node is still heartbeating
 235  * even though we've lost it's conn.  it must only be called after conn_err
 236  * and indicates that we must now make a quorum decision in the future,
 237  * though we might be doing so after waiting for holds to drain.  Here
 238  * we'll be dropping the hold from conn_err. */
 239 void o2quo_hb_still_up(u8 node)
 240 {
 241         struct o2quo_state *qs = &o2quo_state;
 242
 243         spin_lock(&qs->qs_lock);
 244
 245         mlog(0, "node %u\n", node);
 246
 247         qs->qs_pending = 1;
 248         o2quo_clear_hold(qs, node);
 249
 250         spin_unlock(&qs->qs_lock);
 251 }
 252
 253 /* This is analagous to hb_up.  as a node's connection comes up we delay the
 254  * quorum decision until we see it heartbeating.  the hold will be droped in
 255  * hb_up or hb_down.  it might be perpetuated by con_err until hb_down.  if
 256  * it's already heartbeating we we might be dropping a hold that conn_up got.
 257  * */
 258 void o2quo_conn_up(u8 node)
 259 {
 260         struct o2quo_state *qs = &o2quo_state;
 261
 262         spin_lock(&qs->qs_lock);
 263
 264         qs->qs_connected++;
 265         mlog_bug_on_msg(qs->qs_connected == O2NM_MAX_NODES,
 266                         "node %u\n", node);
 267         mlog_bug_on_msg(test_bit(node, qs->qs_conn_bm), "node %u\n", node);
 268         set_bit(node, qs->qs_conn_bm);
 269
 270         mlog(0, "node %u, %d total\n", node, qs->qs_connected);
 271
 272         if (!test_bit(node, qs->qs_hb_bm))
 273                 o2quo_set_hold(qs, node);
 274         else
 275                 o2quo_clear_hold(qs, node);
 276
 277         spin_unlock(&qs->qs_lock);
 278 }
 279
 280 /* we've decided that we won't ever be connecting to the node again.  if it's
 281  * still heartbeating we grab a hold that will delay decisions until either the
 282  * node stops heartbeating from hb_down or the caller decides that the node is
 283  * still up and calls still_up */
 284 void o2quo_conn_err(u8 node)
 285 {
 286         struct o2quo_state *qs = &o2quo_state;
 287
 288         spin_lock(&qs->qs_lock);
 289
 290         if (test_bit(node, qs->qs_conn_bm)) {
 291                 qs->qs_connected--;
 292                 mlog_bug_on_msg(qs->qs_connected < 0,
 293                                 "node %u, connected %d\n",
 294                                 node, qs->qs_connected);
 295
 296                 clear_bit(node, qs->qs_conn_bm);
 297         }
 298
 299         mlog(0, "node %u, %d total\n", node, qs->qs_connected);
 300
 301         if (test_bit(node, qs->qs_hb_bm))
 302                 o2quo_set_hold(qs, node);
 303
 304         spin_unlock(&qs->qs_lock);
 305 }
 306
 307 void o2quo_init(void)
 308 {
 309         struct o2quo_state *qs = &o2quo_state;
 310
 311         spin_lock_init(&qs->qs_lock);
 312         INIT_WORK(&qs->qs_work, o2quo_make_decision);
 313 }
 314
 315 void o2quo_exit(void)
 316 {
 317         flush_scheduled_work();
 318 }