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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/workqueue.h>
48 #include <linux/reboot.h>
49
50 #include "heartbeat.h"
51 #include "nodemanager.h"
52 #define MLOG_MASK_PREFIX ML_QUORUM
53 #include "masklog.h"
54 #include "quorum.h"
55
56 static struct o2quo_state {
57 spinlock_t qs_lock;
58 struct work_struct qs_work;
59 int qs_pending;
60 int qs_heartbeating;
61 unsigned long qs_hb_bm[BITS_TO_LONGS(O2NM_MAX_NODES)];
62 int qs_connected;
63 unsigned long qs_conn_bm[BITS_TO_LONGS(O2NM_MAX_NODES)];
64 int qs_holds;
65 unsigned long qs_hold_bm[BITS_TO_LONGS(O2NM_MAX_NODES)];
66 } o2quo_state;
67
68 /* this is horribly heavy-handed. It should instead flip the file
69 * system RO and call some userspace script. */
70 static void o2quo_fence_self(void)
71 {
72 /* panic spins with interrupts enabled. with preempt
73 * threads can still schedule, etc, etc */
74 o2hb_stop_all_regions();
75
76 switch (o2nm_single_cluster->cl_fence_method) {
77 case O2NM_FENCE_PANIC:
78 panic("*** ocfs2 is very sorry to be fencing this system by "
79 "panicing ***\n");
80 break;
81 default:
82 WARN_ON(o2nm_single_cluster->cl_fence_method >=
83 O2NM_FENCE_METHODS);
84 /* fall through */
85 case O2NM_FENCE_RESET:
86 printk(KERN_ERR "*** ocfs2 is very sorry to be fencing this "
87 "system by restarting ***\n");
88 emergency_restart();
89 break;
90 };
91 }
92
93 /* Indicate that a timeout occurred on a hearbeat region write. The
94 * other nodes in the cluster may consider us dead at that time so we
95 * want to "fence" ourselves so that we don't scribble on the disk
96 * after they think they've recovered us. This can't solve all
97 * problems related to writeout after recovery but this hack can at
98 * least close some of those gaps. When we have real fencing, this can
99 * go away as our node would be fenced externally before other nodes
100 * begin recovery. */
101 void o2quo_disk_timeout(void)
102 {
103 o2quo_fence_self();
104 }
105
106 static void o2quo_make_decision(struct work_struct *work)
107 {
108 int quorum;
109 int lowest_hb, lowest_reachable = 0, fence = 0;
110 struct o2quo_state *qs = &o2quo_state;
111
112 spin_lock(&qs->qs_lock);
113
114 lowest_hb = find_first_bit(qs->qs_hb_bm, O2NM_MAX_NODES);
115 if (lowest_hb != O2NM_MAX_NODES)
116 lowest_reachable = test_bit(lowest_hb, qs->qs_conn_bm);
117
118 mlog(0, "heartbeating: %d, connected: %d, "
119 "lowest: %d (%sreachable)\n", qs->qs_heartbeating,
120 qs->qs_connected, lowest_hb, lowest_reachable ? "" : "un");
121
122 if (!test_bit(o2nm_this_node(), qs->qs_hb_bm) ||
123 qs->qs_heartbeating == 1)
124 goto out;
125
126 if (qs->qs_heartbeating & 1) {
127 /* the odd numbered cluster case is straight forward --
128 * if we can't talk to the majority we're hosed */
129 quorum = (qs->qs_heartbeating + 1)/2;
130 if (qs->qs_connected < quorum) {
131 mlog(ML_ERROR, "fencing this node because it is "
132 "only connected to %u nodes and %u is needed "
133 "to make a quorum out of %u heartbeating nodes\n",
134 qs->qs_connected, quorum,
135 qs->qs_heartbeating);
136 fence = 1;
137 }
138 } else {
139 /* the even numbered cluster adds the possibility of each half
140 * of the cluster being able to talk amongst themselves.. in
141 * that case we're hosed if we can't talk to the group that has
142 * the lowest numbered node */
143 quorum = qs->qs_heartbeating / 2;
144 if (qs->qs_connected < quorum) {
145 mlog(ML_ERROR, "fencing this node because it is "
146 "only connected to %u nodes and %u is needed "
147 "to make a quorum out of %u heartbeating nodes\n",
148 qs->qs_connected, quorum,
149 qs->qs_heartbeating);
150 fence = 1;
151 }
152 else if ((qs->qs_connected == quorum) &&
153 !lowest_reachable) {
154 mlog(ML_ERROR, "fencing this node because it is "
155 "connected to a half-quorum of %u out of %u "
156 "nodes which doesn't include the lowest active "
157 "node %u\n", quorum, qs->qs_heartbeating,
158 lowest_hb);
159 fence = 1;
160 }
161 }
162
163 out:
164 if (fence) {
165 spin_unlock(&qs->qs_lock);
166 o2quo_fence_self();
167 } else {
168 mlog(ML_NOTICE, "not fencing this node, heartbeating: %d, "
169 "connected: %d, lowest: %d (%sreachable)\n",
170 qs->qs_heartbeating, qs->qs_connected, lowest_hb,
171 lowest_reachable ? "" : "un");
172 spin_unlock(&qs->qs_lock);
173
174 }
175
176 }
177
178 static void o2quo_set_hold(struct o2quo_state *qs, u8 node)
179 {
180 assert_spin_locked(&qs->qs_lock);
181
182 if (!test_and_set_bit(node, qs->qs_hold_bm)) {
183 qs->qs_holds++;
184 mlog_bug_on_msg(qs->qs_holds == O2NM_MAX_NODES,
185 "node %u\n", node);
186 mlog(0, "node %u, %d total\n", node, qs->qs_holds);
187 }
188 }
189
190 static void o2quo_clear_hold(struct o2quo_state *qs, u8 node)
191 {
192 assert_spin_locked(&qs->qs_lock);
193
194 if (test_and_clear_bit(node, qs->qs_hold_bm)) {
195 mlog(0, "node %u, %d total\n", node, qs->qs_holds - 1);
196 if (--qs->qs_holds == 0) {
197 if (qs->qs_pending) {
198 qs->qs_pending = 0;
199 schedule_work(&qs->qs_work);
200 }
201 }
202 mlog_bug_on_msg(qs->qs_holds < 0, "node %u, holds %d\n",
203 node, qs->qs_holds);
204 }
205 }
206
207 /* as a node comes up we delay the quorum decision until we know the fate of
208 * the connection. the hold will be droped in conn_up or hb_down. it might be
209 * perpetuated by con_err until hb_down. if we already have a conn, we might
210 * be dropping a hold that conn_up got. */
211 void o2quo_hb_up(u8 node)
212 {
213 struct o2quo_state *qs = &o2quo_state;
214
215 spin_lock(&qs->qs_lock);
216
217 qs->qs_heartbeating++;
218 mlog_bug_on_msg(qs->qs_heartbeating == O2NM_MAX_NODES,
219 "node %u\n", node);
220 mlog_bug_on_msg(test_bit(node, qs->qs_hb_bm), "node %u\n", node);
221 set_bit(node, qs->qs_hb_bm);
222
223 mlog(0, "node %u, %d total\n", node, qs->qs_heartbeating);
224
225 if (!test_bit(node, qs->qs_conn_bm))
226 o2quo_set_hold(qs, node);
227 else
228 o2quo_clear_hold(qs, node);
229
230 spin_unlock(&qs->qs_lock);
231 }
232
233 /* hb going down releases any holds we might have had due to this node from
234 * conn_up, conn_err, or hb_up */
235 void o2quo_hb_down(u8 node)
236 {
237 struct o2quo_state *qs = &o2quo_state;
238
239 spin_lock(&qs->qs_lock);
240
241 qs->qs_heartbeating--;
242 mlog_bug_on_msg(qs->qs_heartbeating < 0,
243 "node %u, %d heartbeating\n",
244 node, qs->qs_heartbeating);
245 mlog_bug_on_msg(!test_bit(node, qs->qs_hb_bm), "node %u\n", node);
246 clear_bit(node, qs->qs_hb_bm);
247
248 mlog(0, "node %u, %d total\n", node, qs->qs_heartbeating);
249
250 o2quo_clear_hold(qs, node);
251
252 spin_unlock(&qs->qs_lock);
253 }
254
255 /* this tells us that we've decided that the node is still heartbeating
256 * even though we've lost it's conn. it must only be called after conn_err
257 * and indicates that we must now make a quorum decision in the future,
258 * though we might be doing so after waiting for holds to drain. Here
259 * we'll be dropping the hold from conn_err. */
260 void o2quo_hb_still_up(u8 node)
261 {
262 struct o2quo_state *qs = &o2quo_state;
263
264 spin_lock(&qs->qs_lock);
265
266 mlog(0, "node %u\n", node);
267
268 qs->qs_pending = 1;
269 o2quo_clear_hold(qs, node);
270
271 spin_unlock(&qs->qs_lock);
272 }
273
274 /* This is analogous to hb_up. as a node's connection comes up we delay the
275 * quorum decision until we see it heartbeating. the hold will be droped in
276 * hb_up or hb_down. it might be perpetuated by con_err until hb_down. if
277 * it's already heartbeating we might be dropping a hold that conn_up got.
278 * */
279 void o2quo_conn_up(u8 node)
280 {
281 struct o2quo_state *qs = &o2quo_state;
282
283 spin_lock(&qs->qs_lock);
284
285 qs->qs_connected++;
286 mlog_bug_on_msg(qs->qs_connected == O2NM_MAX_NODES,
287 "node %u\n", node);
288 mlog_bug_on_msg(test_bit(node, qs->qs_conn_bm), "node %u\n", node);
289 set_bit(node, qs->qs_conn_bm);
290
291 mlog(0, "node %u, %d total\n", node, qs->qs_connected);
292
293 if (!test_bit(node, qs->qs_hb_bm))
294 o2quo_set_hold(qs, node);
295 else
296 o2quo_clear_hold(qs, node);
297
298 spin_unlock(&qs->qs_lock);
299 }
300
301 /* we've decided that we won't ever be connecting to the node again. if it's
302 * still heartbeating we grab a hold that will delay decisions until either the
303 * node stops heartbeating from hb_down or the caller decides that the node is
304 * still up and calls still_up */
305 void o2quo_conn_err(u8 node)
306 {
307 struct o2quo_state *qs = &o2quo_state;
308
309 spin_lock(&qs->qs_lock);
310
311 if (test_bit(node, qs->qs_conn_bm)) {
312 qs->qs_connected--;
313 mlog_bug_on_msg(qs->qs_connected < 0,
314 "node %u, connected %d\n",
315 node, qs->qs_connected);
316
317 clear_bit(node, qs->qs_conn_bm);
318
319 if (test_bit(node, qs->qs_hb_bm))
320 o2quo_set_hold(qs, node);
321 }
322
323 mlog(0, "node %u, %d total\n", node, qs->qs_connected);
324
325
326 spin_unlock(&qs->qs_lock);
327 }
328
329 void o2quo_init(void)
330 {
331 struct o2quo_state *qs = &o2quo_state;
332
333 spin_lock_init(&qs->qs_lock);
334 INIT_WORK(&qs->qs_work, o2quo_make_decision);
335 }
336
337 void o2quo_exit(void)
338 {
339 struct o2quo_state *qs = &o2quo_state;
340
341 flush_work(&qs->qs_work);
342 }