1/*-------------------------------------------------------------------------
2 *
3 * procsignal.c
4 * Routines for interprocess signalling
5 *
6 *
7 * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
8 * Portions Copyright (c) 1994, Regents of the University of California
9 *
10 * IDENTIFICATION
11 * src/backend/storage/ipc/procsignal.c
12 *
13 *-------------------------------------------------------------------------
14 */
15#include "postgres.h"
16
17#include <signal.h>
18#include <unistd.h>
19
20#include "access/parallel.h"
21#include "commands/async.h"
22#include "miscadmin.h"
23#include "replication/walsender.h"
24#include "storage/latch.h"
25#include "storage/ipc.h"
26#include "storage/proc.h"
27#include "storage/shmem.h"
28#include "storage/sinval.h"
29#include "tcop/tcopprot.h"
30
31
32/*
33 * The SIGUSR1 signal is multiplexed to support signalling multiple event
34 * types. The specific reason is communicated via flags in shared memory.
35 * We keep a boolean flag for each possible "reason", so that different
36 * reasons can be signaled to a process concurrently. (However, if the same
37 * reason is signaled more than once nearly simultaneously, the process may
38 * observe it only once.)
39 *
40 * Each process that wants to receive signals registers its process ID
41 * in the ProcSignalSlots array. The array is indexed by backend ID to make
42 * slot allocation simple, and to avoid having to search the array when you
43 * know the backend ID of the process you're signalling. (We do support
44 * signalling without backend ID, but it's a bit less efficient.)
45 *
46 * The flags are actually declared as "volatile sig_atomic_t" for maximum
47 * portability. This should ensure that loads and stores of the flag
48 * values are atomic, allowing us to dispense with any explicit locking.
49 */
50typedef struct
51{
52 pid_t pss_pid;
53 sig_atomic_t pss_signalFlags[NUM_PROCSIGNALS];
54} ProcSignalSlot;
55
56/*
57 * We reserve a slot for each possible BackendId, plus one for each
58 * possible auxiliary process type. (This scheme assumes there is not
59 * more than one of any auxiliary process type at a time.)
60 */
61#define NumProcSignalSlots (MaxBackends + NUM_AUXPROCTYPES)
62
63static ProcSignalSlot *ProcSignalSlots = NULL;
64static volatile ProcSignalSlot *MyProcSignalSlot = NULL;
65
66static bool CheckProcSignal(ProcSignalReason reason);
67static void CleanupProcSignalState(int status, Datum arg);
68
69/*
70 * ProcSignalShmemSize
71 * Compute space needed for procsignal's shared memory
72 */
73Size
74ProcSignalShmemSize(void)
75{
76 return NumProcSignalSlots * sizeof(ProcSignalSlot);
77}
78
79/*
80 * ProcSignalShmemInit
81 * Allocate and initialize procsignal's shared memory
82 */
83void
84ProcSignalShmemInit(void)
85{
86 Size size = ProcSignalShmemSize();
87 bool found;
88
89 ProcSignalSlots = (ProcSignalSlot *)
90 ShmemInitStruct("ProcSignalSlots", size, &found);
91
92 /* If we're first, set everything to zeroes */
93 if (!found)
94 MemSet(ProcSignalSlots, 0, size);
95}
96
97/*
98 * ProcSignalInit
99 * Register the current process in the procsignal array
100 *
101 * The passed index should be my BackendId if the process has one,
102 * or MaxBackends + aux process type if not.
103 */
104void
105ProcSignalInit(int pss_idx)
106{
107 volatile ProcSignalSlot *slot;
108
109 Assert(pss_idx >= 1 && pss_idx <= NumProcSignalSlots);
110
111 slot = &ProcSignalSlots[pss_idx - 1];
112
113 /* sanity check */
114 if (slot->pss_pid != 0)
115 elog(LOG, "process %d taking over ProcSignal slot %d, but it's not empty",
116 MyProcPid, pss_idx);
117
118 /* Clear out any leftover signal reasons */
119 MemSet(slot->pss_signalFlags, 0, NUM_PROCSIGNALS * sizeof(sig_atomic_t));
120
121 /* Mark slot with my PID */
122 slot->pss_pid = MyProcPid;
123
124 /* Remember slot location for CheckProcSignal */
125 MyProcSignalSlot = slot;
126
127 /* Set up to release the slot on process exit */
128 on_shmem_exit(CleanupProcSignalState, Int32GetDatum(pss_idx));
129}
130
131/*
132 * CleanupProcSignalState
133 * Remove current process from ProcSignalSlots
134 *
135 * This function is called via on_shmem_exit() during backend shutdown.
136 */
137static void
138CleanupProcSignalState(int status, Datum arg)
139{
140 int pss_idx = DatumGetInt32(arg);
141 volatile ProcSignalSlot *slot;
142
143 slot = &ProcSignalSlots[pss_idx - 1];
144 Assert(slot == MyProcSignalSlot);
145
146 /*
147 * Clear MyProcSignalSlot, so that a SIGUSR1 received after this point
148 * won't try to access it after it's no longer ours (and perhaps even
149 * after we've unmapped the shared memory segment).
150 */
151 MyProcSignalSlot = NULL;
152
153 /* sanity check */
154 if (slot->pss_pid != MyProcPid)
155 {
156 /*
157 * don't ERROR here. We're exiting anyway, and don't want to get into
158 * infinite loop trying to exit
159 */
160 elog(LOG, "process %d releasing ProcSignal slot %d, but it contains %d",
161 MyProcPid, pss_idx, (int) slot->pss_pid);
162 return; /* XXX better to zero the slot anyway? */
163 }
164
165 slot->pss_pid = 0;
166}
167
168/*
169 * SendProcSignal
170 * Send a signal to a Postgres process
171 *
172 * Providing backendId is optional, but it will speed up the operation.
173 *
174 * On success (a signal was sent), zero is returned.
175 * On error, -1 is returned, and errno is set (typically to ESRCH or EPERM).
176 *
177 * Not to be confused with ProcSendSignal
178 */
179int
180SendProcSignal(pid_t pid, ProcSignalReason reason, BackendId backendId)
181{
182 volatile ProcSignalSlot *slot;
183
184 if (backendId != InvalidBackendId)
185 {
186 slot = &ProcSignalSlots[backendId - 1];
187
188 /*
189 * Note: Since there's no locking, it's possible that the target
190 * process detaches from shared memory and exits right after this
191 * test, before we set the flag and send signal. And the signal slot
192 * might even be recycled by a new process, so it's remotely possible
193 * that we set a flag for a wrong process. That's OK, all the signals
194 * are such that no harm is done if they're mistakenly fired.
195 */
196 if (slot->pss_pid == pid)
197 {
198 /* Atomically set the proper flag */
199 slot->pss_signalFlags[reason] = true;
200 /* Send signal */
201 return kill(pid, SIGUSR1);
202 }
203 }
204 else
205 {
206 /*
207 * BackendId not provided, so search the array using pid. We search
208 * the array back to front so as to reduce search overhead. Passing
209 * InvalidBackendId means that the target is most likely an auxiliary
210 * process, which will have a slot near the end of the array.
211 */
212 int i;
213
214 for (i = NumProcSignalSlots - 1; i >= 0; i--)
215 {
216 slot = &ProcSignalSlots[i];
217
218 if (slot->pss_pid == pid)
219 {
220 /* the above note about race conditions applies here too */
221
222 /* Atomically set the proper flag */
223 slot->pss_signalFlags[reason] = true;
224 /* Send signal */
225 return kill(pid, SIGUSR1);
226 }
227 }
228 }
229
230 errno = ESRCH;
231 return -1;
232}
233
234/*
235 * CheckProcSignal - check to see if a particular reason has been
236 * signaled, and clear the signal flag. Should be called after receiving
237 * SIGUSR1.
238 */
239static bool
240CheckProcSignal(ProcSignalReason reason)
241{
242 volatile ProcSignalSlot *slot = MyProcSignalSlot;
243
244 if (slot != NULL)
245 {
246 /* Careful here --- don't clear flag if we haven't seen it set */
247 if (slot->pss_signalFlags[reason])
248 {
249 slot->pss_signalFlags[reason] = false;
250 return true;
251 }
252 }
253
254 return false;
255}
256
257/*
258 * procsignal_sigusr1_handler - handle SIGUSR1 signal.
259 */
260void
261procsignal_sigusr1_handler(SIGNAL_ARGS)
262{
263 int save_errno = errno;
264
265 if (CheckProcSignal(PROCSIG_CATCHUP_INTERRUPT))
266 HandleCatchupInterrupt();
267
268 if (CheckProcSignal(PROCSIG_NOTIFY_INTERRUPT))
269 HandleNotifyInterrupt();
270
271 if (CheckProcSignal(PROCSIG_PARALLEL_MESSAGE))
272 HandleParallelMessageInterrupt();
273
274 if (CheckProcSignal(PROCSIG_WALSND_INIT_STOPPING))
275 HandleWalSndInitStopping();
276
277 if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_DATABASE))
278 RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_DATABASE);
279
280 if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_TABLESPACE))
281 RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_TABLESPACE);
282
283 if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_LOCK))
284 RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_LOCK);
285
286 if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_SNAPSHOT))
287 RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_SNAPSHOT);
288
289 if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK))
290 RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK);
291
292 if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN))
293 RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
294
295 SetLatch(MyLatch);
296
297 latch_sigusr1_handler();
298
299 errno = save_errno;
300}
301