1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 *
4 * Copyright (C) 2005 Oracle. All rights reserved.
5 */
6
7 /* This quorum hack is only here until we transition to some more rational
8 * approach that is driven from userspace. Honest. No foolin'.
9 *
10 * Imagine two nodes lose network connectivity to each other but they're still
11 * up and operating in every other way. Presumably a network timeout indicates
12 * that a node is broken and should be recovered. They can't both recover each
13 * other and both carry on without serialising their access to the file system.
14 * They need to decide who is authoritative. Now extend that problem to
15 * arbitrary groups of nodes losing connectivity between each other.
16 *
17 * So we declare that a node which has given up on connecting to a majority
18 * of nodes who are still heartbeating will fence itself.
19 *
20 * There are huge opportunities for races here. After we give up on a node's
21 * connection we need to wait long enough to give heartbeat an opportunity
22 * to declare the node as truly dead. We also need to be careful with the
23 * race between when we see a node start heartbeating and when we connect
24 * to it.
25 *
26 * So nodes that are in this transtion put a hold on the quorum decision
27 * with a counter. As they fall out of this transition they drop the count
28 * and if they're the last, they fire off the decision.
29 */
30 #include <linux/kernel.h>
31 #include <linux/workqueue.h>
32 #include <linux/reboot.h>
33
34 #include "heartbeat.h"
35 #include "nodemanager.h"
36 #define MLOG_MASK_PREFIX ML_QUORUM
37 #include "masklog.h"
38 #include "quorum.h"
39
40 static struct o2quo_state {
41 spinlock_t qs_lock;
42 struct work_struct qs_work;
43 int qs_pending;
44 int qs_heartbeating;
45 unsigned long qs_hb_bm[BITS_TO_LONGS(O2NM_MAX_NODES)];
46 int qs_connected;
47 unsigned long qs_conn_bm[BITS_TO_LONGS(O2NM_MAX_NODES)];
48 int qs_holds;
49 unsigned long qs_hold_bm[BITS_TO_LONGS(O2NM_MAX_NODES)];
50 } o2quo_state;
51
52 /* this is horribly heavy-handed. It should instead flip the file
53 * system RO and call some userspace script. */
54 static void o2quo_fence_self(void)
55 {
56 /* panic spins with interrupts enabled. with preempt
57 * threads can still schedule, etc, etc */
58 o2hb_stop_all_regions();
59
60 switch (o2nm_single_cluster->cl_fence_method) {
61 case O2NM_FENCE_PANIC:
62 panic("*** ocfs2 is very sorry to be fencing this system by "
63 "panicing ***\n");
64 break;
65 default:
66 WARN_ON(o2nm_single_cluster->cl_fence_method >=
67 O2NM_FENCE_METHODS);
68 fallthrough;
69 case O2NM_FENCE_RESET:
70 printk(KERN_ERR "*** ocfs2 is very sorry to be fencing this "
71 "system by restarting ***\n");
72 emergency_restart();
73 break;
74 }
75 }
76
77 /* Indicate that a timeout occurred on a heartbeat region write. The
78 * other nodes in the cluster may consider us dead at that time so we
79 * want to "fence" ourselves so that we don't scribble on the disk
80 * after they think they've recovered us. This can't solve all
81 * problems related to writeout after recovery but this hack can at
82 * least close some of those gaps. When we have real fencing, this can
83 * go away as our node would be fenced externally before other nodes
84 * begin recovery. */
85 void o2quo_disk_timeout(void)
86 {
87 o2quo_fence_self();
88 }
89
90 static void o2quo_make_decision(struct work_struct *work)
91 {
92 int quorum;
93 int lowest_hb, lowest_reachable = 0, fence = 0;
94 struct o2quo_state *qs = &o2quo_state;
95
96 spin_lock_bh(&qs->qs_lock);
97
98 lowest_hb = find_first_bit(qs->qs_hb_bm, O2NM_MAX_NODES);
99 if (lowest_hb != O2NM_MAX_NODES)
100 lowest_reachable = test_bit(lowest_hb, qs->qs_conn_bm);
101
102 mlog(0, "heartbeating: %d, connected: %d, "
103 "lowest: %d (%sreachable)\n", qs->qs_heartbeating,
104 qs->qs_connected, lowest_hb, lowest_reachable ? "" : "un");
105
106 if (!test_bit(o2nm_this_node(), qs->qs_hb_bm) ||
107 qs->qs_heartbeating == 1)
108 goto out;
109
110 if (qs->qs_heartbeating & 1) {
111 /* the odd numbered cluster case is straight forward --
112 * if we can't talk to the majority we're hosed */
113 quorum = (qs->qs_heartbeating + 1)/2;
114 if (qs->qs_connected < quorum) {
115 mlog(ML_ERROR, "fencing this node because it is "
116 "only connected to %u nodes and %u is needed "
117 "to make a quorum out of %u heartbeating nodes\n",
118 qs->qs_connected, quorum,
119 qs->qs_heartbeating);
120 fence = 1;
121 }
122 } else {
123 /* the even numbered cluster adds the possibility of each half
124 * of the cluster being able to talk amongst themselves.. in
125 * that case we're hosed if we can't talk to the group that has
126 * the lowest numbered node */
127 quorum = qs->qs_heartbeating / 2;
128 if (qs->qs_connected < quorum) {
129 mlog(ML_ERROR, "fencing this node because it is "
130 "only connected to %u nodes and %u is needed "
131 "to make a quorum out of %u heartbeating nodes\n",
132 qs->qs_connected, quorum,
133 qs->qs_heartbeating);
134 fence = 1;
135 }
136 else if ((qs->qs_connected == quorum) &&
137 !lowest_reachable) {
138 mlog(ML_ERROR, "fencing this node because it is "
139 "connected to a half-quorum of %u out of %u "
140 "nodes which doesn't include the lowest active "
141 "node %u\n", quorum, qs->qs_heartbeating,
142 lowest_hb);
143 fence = 1;
144 }
145 }
146
147 out:
148 if (fence) {
149 spin_unlock_bh(&qs->qs_lock);
150 o2quo_fence_self();
151 } else {
152 mlog(ML_NOTICE, "not fencing this node, heartbeating: %d, "
153 "connected: %d, lowest: %d (%sreachable)\n",
154 qs->qs_heartbeating, qs->qs_connected, lowest_hb,
155 lowest_reachable ? "" : "un");
156 spin_unlock_bh(&qs->qs_lock);
157
158 }
159
160 }
161
162 static void o2quo_set_hold(struct o2quo_state *qs, u8 node)
163 {
164 assert_spin_locked(&qs->qs_lock);
165
166 if (!test_and_set_bit(node, qs->qs_hold_bm)) {
167 qs->qs_holds++;
168 mlog_bug_on_msg(qs->qs_holds == O2NM_MAX_NODES,
169 "node %u\n", node);
170 mlog(0, "node %u, %d total\n", node, qs->qs_holds);
171 }
172 }
173
174 static void o2quo_clear_hold(struct o2quo_state *qs, u8 node)
175 {
176 assert_spin_locked(&qs->qs_lock);
177
178 if (test_and_clear_bit(node, qs->qs_hold_bm)) {
179 mlog(0, "node %u, %d total\n", node, qs->qs_holds - 1);
180 if (--qs->qs_holds == 0) {
181 if (qs->qs_pending) {
182 qs->qs_pending = 0;
183 schedule_work(&qs->qs_work);
184 }
185 }
186 mlog_bug_on_msg(qs->qs_holds < 0, "node %u, holds %d\n",
187 node, qs->qs_holds);
188 }
189 }
190
191 /* as a node comes up we delay the quorum decision until we know the fate of
192 * the connection. the hold will be droped in conn_up or hb_down. it might be
193 * perpetuated by con_err until hb_down. if we already have a conn, we might
194 * be dropping a hold that conn_up got. */
195 void o2quo_hb_up(u8 node)
196 {
197 struct o2quo_state *qs = &o2quo_state;
198
199 spin_lock_bh(&qs->qs_lock);
200
201 qs->qs_heartbeating++;
202 mlog_bug_on_msg(qs->qs_heartbeating == O2NM_MAX_NODES,
203 "node %u\n", node);
204 mlog_bug_on_msg(test_bit(node, qs->qs_hb_bm), "node %u\n", node);
205 set_bit(node, qs->qs_hb_bm);
206
207 mlog(0, "node %u, %d total\n", node, qs->qs_heartbeating);
208
209 if (!test_bit(node, qs->qs_conn_bm))
210 o2quo_set_hold(qs, node);
211 else
212 o2quo_clear_hold(qs, node);
213
214 spin_unlock_bh(&qs->qs_lock);
215 }
216
217 /* hb going down releases any holds we might have had due to this node from
218 * conn_up, conn_err, or hb_up */
219 void o2quo_hb_down(u8 node)
220 {
221 struct o2quo_state *qs = &o2quo_state;
222
223 spin_lock_bh(&qs->qs_lock);
224
225 qs->qs_heartbeating--;
226 mlog_bug_on_msg(qs->qs_heartbeating < 0,
227 "node %u, %d heartbeating\n",
228 node, qs->qs_heartbeating);
229 mlog_bug_on_msg(!test_bit(node, qs->qs_hb_bm), "node %u\n", node);
230 clear_bit(node, qs->qs_hb_bm);
231
232 mlog(0, "node %u, %d total\n", node, qs->qs_heartbeating);
233
234 o2quo_clear_hold(qs, node);
235
236 spin_unlock_bh(&qs->qs_lock);
237 }
238
239 /* this tells us that we've decided that the node is still heartbeating
240 * even though we've lost it's conn. it must only be called after conn_err
241 * and indicates that we must now make a quorum decision in the future,
242 * though we might be doing so after waiting for holds to drain. Here
243 * we'll be dropping the hold from conn_err. */
244 void o2quo_hb_still_up(u8 node)
245 {
246 struct o2quo_state *qs = &o2quo_state;
247
248 spin_lock_bh(&qs->qs_lock);
249
250 mlog(0, "node %u\n", node);
251
252 qs->qs_pending = 1;
253 o2quo_clear_hold(qs, node);
254
255 spin_unlock_bh(&qs->qs_lock);
256 }
257
258 /* This is analogous to hb_up. as a node's connection comes up we delay the
259 * quorum decision until we see it heartbeating. the hold will be droped in
260 * hb_up or hb_down. it might be perpetuated by con_err until hb_down. if
261 * it's already heartbeating we might be dropping a hold that conn_up got.
262 * */
263 void o2quo_conn_up(u8 node)
264 {
265 struct o2quo_state *qs = &o2quo_state;
266
267 spin_lock_bh(&qs->qs_lock);
268
269 qs->qs_connected++;
270 mlog_bug_on_msg(qs->qs_connected == O2NM_MAX_NODES,
271 "node %u\n", node);
272 mlog_bug_on_msg(test_bit(node, qs->qs_conn_bm), "node %u\n", node);
273 set_bit(node, qs->qs_conn_bm);
274
275 mlog(0, "node %u, %d total\n", node, qs->qs_connected);
276
277 if (!test_bit(node, qs->qs_hb_bm))
278 o2quo_set_hold(qs, node);
279 else
280 o2quo_clear_hold(qs, node);
281
282 spin_unlock_bh(&qs->qs_lock);
283 }
284
285 /* we've decided that we won't ever be connecting to the node again. if it's
286 * still heartbeating we grab a hold that will delay decisions until either the
287 * node stops heartbeating from hb_down or the caller decides that the node is
288 * still up and calls still_up */
289 void o2quo_conn_err(u8 node)
290 {
291 struct o2quo_state *qs = &o2quo_state;
292
293 spin_lock_bh(&qs->qs_lock);
294
295 if (test_bit(node, qs->qs_conn_bm)) {
296 qs->qs_connected--;
297 mlog_bug_on_msg(qs->qs_connected < 0,
298 "node %u, connected %d\n",
299 node, qs->qs_connected);
300
301 clear_bit(node, qs->qs_conn_bm);
302
303 if (test_bit(node, qs->qs_hb_bm))
304 o2quo_set_hold(qs, node);
305 }
306
307 mlog(0, "node %u, %d total\n", node, qs->qs_connected);
308
309
310 spin_unlock_bh(&qs->qs_lock);
311 }
312
313 void o2quo_init(void)
314 {
315 struct o2quo_state *qs = &o2quo_state;
316
317 spin_lock_init(&qs->qs_lock);
318 INIT_WORK(&qs->qs_work, o2quo_make_decision);
319 }
320
321 void o2quo_exit(void)
322 {
323 struct o2quo_state *qs = &o2quo_state;
324
325 flush_work(&qs->qs_work);
326 }
327
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