Adding upstream version 15.4.upstream/15.4upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 517 insertions, 0 deletions

diff --git a/src/backend/port/sysv_sema.c b/src/backend/port/sysv_sema.c
new file mode 100644
index 0000000..ea3ad6d
--- /dev/null
+++ b/src/backend/port/sysv_sema.c
@@ -0,0 +1,517 @@
+/*-------------------------------------------------------------------------
+ *
+ * sysv_sema.c
+ *	  Implement PGSemaphores using SysV semaphore facilities
+ *
+ *
+ * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/backend/port/sysv_sema.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <signal.h>
+#include <unistd.h>
+#include <sys/file.h>
+#include <sys/stat.h>
+#ifdef HAVE_SYS_IPC_H
+#include <sys/ipc.h>
+#endif
+#ifdef HAVE_SYS_SEM_H
+#include <sys/sem.h>
+#endif
+
+#include "miscadmin.h"
+#include "storage/ipc.h"
+#include "storage/pg_sema.h"
+#include "storage/shmem.h"
+
+
+typedef struct PGSemaphoreData
+{
+	int			semId;			/* semaphore set identifier */
+	int			semNum;			/* semaphore number within set */
+} PGSemaphoreData;
+
+#ifndef HAVE_UNION_SEMUN
+union semun
+{
+	int			val;
+	struct semid_ds *buf;
+	unsigned short *array;
+};
+#endif
+
+typedef key_t IpcSemaphoreKey;	/* semaphore key passed to semget(2) */
+typedef int IpcSemaphoreId;		/* semaphore ID returned by semget(2) */
+
+/*
+ * SEMAS_PER_SET is the number of useful semaphores in each semaphore set
+ * we allocate.  It must be *less than* your kernel's SEMMSL (max semaphores
+ * per set) parameter, which is often around 25.  (Less than, because we
+ * allocate one extra sema in each set for identification purposes.)
+ */
+#define SEMAS_PER_SET	16
+
+#define IPCProtection	(0600)	/* access/modify by user only */
+
+#define PGSemaMagic		537		/* must be less than SEMVMX */
+
+
+static PGSemaphore sharedSemas; /* array of PGSemaphoreData in shared memory */
+static int	numSharedSemas;		/* number of PGSemaphoreDatas used so far */
+static int	maxSharedSemas;		/* allocated size of PGSemaphoreData array */
+static IpcSemaphoreId *mySemaSets;	/* IDs of sema sets acquired so far */
+static int	numSemaSets;		/* number of sema sets acquired so far */
+static int	maxSemaSets;		/* allocated size of mySemaSets array */
+static IpcSemaphoreKey nextSemaKey; /* next key to try using */
+static int	nextSemaNumber;		/* next free sem num in last sema set */
+
+
+static IpcSemaphoreId InternalIpcSemaphoreCreate(IpcSemaphoreKey semKey,
+												 int numSems);
+static void IpcSemaphoreInitialize(IpcSemaphoreId semId, int semNum,
+								   int value);
+static void IpcSemaphoreKill(IpcSemaphoreId semId);
+static int	IpcSemaphoreGetValue(IpcSemaphoreId semId, int semNum);
+static pid_t IpcSemaphoreGetLastPID(IpcSemaphoreId semId, int semNum);
+static IpcSemaphoreId IpcSemaphoreCreate(int numSems);
+static void ReleaseSemaphores(int status, Datum arg);
+
+
+/*
+ * InternalIpcSemaphoreCreate
+ *
+ * Attempt to create a new semaphore set with the specified key.
+ * Will fail (return -1) if such a set already exists.
+ *
+ * If we fail with a failure code other than collision-with-existing-set,
+ * print out an error and abort.  Other types of errors suggest nonrecoverable
+ * problems.
+ */
+static IpcSemaphoreId
+InternalIpcSemaphoreCreate(IpcSemaphoreKey semKey, int numSems)
+{
+	int			semId;
+
+	semId = semget(semKey, numSems, IPC_CREAT | IPC_EXCL | IPCProtection);
+
+	if (semId < 0)
+	{
+		int			saved_errno = errno;
+
+		/*
+		 * Fail quietly if error indicates a collision with existing set. One
+		 * would expect EEXIST, given that we said IPC_EXCL, but perhaps we
+		 * could get a permission violation instead?  Also, EIDRM might occur
+		 * if an old set is slated for destruction but not gone yet.
+		 */
+		if (saved_errno == EEXIST || saved_errno == EACCES
+#ifdef EIDRM
+			|| saved_errno == EIDRM
+#endif
+			)
+			return -1;
+
+		/*
+		 * Else complain and abort
+		 */
+		ereport(FATAL,
+				(errmsg("could not create semaphores: %m"),
+				 errdetail("Failed system call was semget(%lu, %d, 0%o).",
+						   (unsigned long) semKey, numSems,
+						   IPC_CREAT | IPC_EXCL | IPCProtection),
+				 (saved_errno == ENOSPC) ?
+				 errhint("This error does *not* mean that you have run out of disk space.  "
+						 "It occurs when either the system limit for the maximum number of "
+						 "semaphore sets (SEMMNI), or the system wide maximum number of "
+						 "semaphores (SEMMNS), would be exceeded.  You need to raise the "
+						 "respective kernel parameter.  Alternatively, reduce PostgreSQL's "
+						 "consumption of semaphores by reducing its max_connections parameter.\n"
+						 "The PostgreSQL documentation contains more information about "
+						 "configuring your system for PostgreSQL.") : 0));
+	}
+
+	return semId;
+}
+
+/*
+ * Initialize a semaphore to the specified value.
+ */
+static void
+IpcSemaphoreInitialize(IpcSemaphoreId semId, int semNum, int value)
+{
+	union semun semun;
+
+	semun.val = value;
+	if (semctl(semId, semNum, SETVAL, semun) < 0)
+	{
+		int			saved_errno = errno;
+
+		ereport(FATAL,
+				(errmsg_internal("semctl(%d, %d, SETVAL, %d) failed: %m",
+								 semId, semNum, value),
+				 (saved_errno == ERANGE) ?
+				 errhint("You possibly need to raise your kernel's SEMVMX value to be at least "
+						 "%d.  Look into the PostgreSQL documentation for details.",
+						 value) : 0));
+	}
+}
+
+/*
+ * IpcSemaphoreKill(semId)	- removes a semaphore set
+ */
+static void
+IpcSemaphoreKill(IpcSemaphoreId semId)
+{
+	union semun semun;
+
+	semun.val = 0;				/* unused, but keep compiler quiet */
+
+	if (semctl(semId, 0, IPC_RMID, semun) < 0)
+		elog(LOG, "semctl(%d, 0, IPC_RMID, ...) failed: %m", semId);
+}
+
+/* Get the current value (semval) of the semaphore */
+static int
+IpcSemaphoreGetValue(IpcSemaphoreId semId, int semNum)
+{
+	union semun dummy;			/* for Solaris */
+
+	dummy.val = 0;				/* unused */
+
+	return semctl(semId, semNum, GETVAL, dummy);
+}
+
+/* Get the PID of the last process to do semop() on the semaphore */
+static pid_t
+IpcSemaphoreGetLastPID(IpcSemaphoreId semId, int semNum)
+{
+	union semun dummy;			/* for Solaris */
+
+	dummy.val = 0;				/* unused */
+
+	return semctl(semId, semNum, GETPID, dummy);
+}
+
+
+/*
+ * Create a semaphore set with the given number of useful semaphores
+ * (an additional sema is actually allocated to serve as identifier).
+ * Dead Postgres sema sets are recycled if found, but we do not fail
+ * upon collision with non-Postgres sema sets.
+ *
+ * The idea here is to detect and re-use keys that may have been assigned
+ * by a crashed postmaster or backend.
+ */
+static IpcSemaphoreId
+IpcSemaphoreCreate(int numSems)
+{
+	IpcSemaphoreId semId;
+	union semun semun;
+	PGSemaphoreData mysema;
+
+	/* Loop till we find a free IPC key */
+	for (nextSemaKey++;; nextSemaKey++)
+	{
+		pid_t		creatorPID;
+
+		/* Try to create new semaphore set */
+		semId = InternalIpcSemaphoreCreate(nextSemaKey, numSems + 1);
+		if (semId >= 0)
+			break;				/* successful create */
+
+		/* See if it looks to be leftover from a dead Postgres process */
+		semId = semget(nextSemaKey, numSems + 1, 0);
+		if (semId < 0)
+			continue;			/* failed: must be some other app's */
+		if (IpcSemaphoreGetValue(semId, numSems) != PGSemaMagic)
+			continue;			/* sema belongs to a non-Postgres app */
+
+		/*
+		 * If the creator PID is my own PID or does not belong to any extant
+		 * process, it's safe to zap it.
+		 */
+		creatorPID = IpcSemaphoreGetLastPID(semId, numSems);
+		if (creatorPID <= 0)
+			continue;			/* oops, GETPID failed */
+		if (creatorPID != getpid())
+		{
+			if (kill(creatorPID, 0) == 0 || errno != ESRCH)
+				continue;		/* sema belongs to a live process */
+		}
+
+		/*
+		 * The sema set appears to be from a dead Postgres process, or from a
+		 * previous cycle of life in this same process.  Zap it, if possible.
+		 * This probably shouldn't fail, but if it does, assume the sema set
+		 * belongs to someone else after all, and continue quietly.
+		 */
+		semun.val = 0;			/* unused, but keep compiler quiet */
+		if (semctl(semId, 0, IPC_RMID, semun) < 0)
+			continue;
+
+		/*
+		 * Now try again to create the sema set.
+		 */
+		semId = InternalIpcSemaphoreCreate(nextSemaKey, numSems + 1);
+		if (semId >= 0)
+			break;				/* successful create */
+
+		/*
+		 * Can only get here if some other process managed to create the same
+		 * sema key before we did.  Let him have that one, loop around to try
+		 * next key.
+		 */
+	}
+
+	/*
+	 * OK, we created a new sema set.  Mark it as created by this process. We
+	 * do this by setting the spare semaphore to PGSemaMagic-1 and then
+	 * incrementing it with semop().  That leaves it with value PGSemaMagic
+	 * and sempid referencing this process.
+	 */
+	IpcSemaphoreInitialize(semId, numSems, PGSemaMagic - 1);
+	mysema.semId = semId;
+	mysema.semNum = numSems;
+	PGSemaphoreUnlock(&mysema);
+
+	return semId;
+}
+
+
+/*
+ * Report amount of shared memory needed for semaphores
+ */
+Size
+PGSemaphoreShmemSize(int maxSemas)
+{
+	return mul_size(maxSemas, sizeof(PGSemaphoreData));
+}
+
+/*
+ * PGReserveSemaphores --- initialize semaphore support
+ *
+ * This is called during postmaster start or shared memory reinitialization.
+ * It should do whatever is needed to be able to support up to maxSemas
+ * subsequent PGSemaphoreCreate calls.  Also, if any system resources
+ * are acquired here or in PGSemaphoreCreate, register an on_shmem_exit
+ * callback to release them.
+ *
+ * In the SysV implementation, we acquire semaphore sets on-demand; the
+ * maxSemas parameter is just used to size the arrays.  There is an array
+ * of PGSemaphoreData structs in shared memory, and a postmaster-local array
+ * with one entry per SysV semaphore set, which we use for releasing the
+ * semaphore sets when done.  (This design ensures that postmaster shutdown
+ * doesn't rely on the contents of shared memory, which a failed backend might
+ * have clobbered.)
+ */
+void
+PGReserveSemaphores(int maxSemas)
+{
+	struct stat statbuf;
+
+	/*
+	 * We use the data directory's inode number to seed the search for free
+	 * semaphore keys.  This minimizes the odds of collision with other
+	 * postmasters, while maximizing the odds that we will detect and clean up
+	 * semaphores left over from a crashed postmaster in our own directory.
+	 */
+	if (stat(DataDir, &statbuf) < 0)
+		ereport(FATAL,
+				(errcode_for_file_access(),
+				 errmsg("could not stat data directory \"%s\": %m",
+						DataDir)));
+
+	/*
+	 * We must use ShmemAllocUnlocked(), since the spinlock protecting
+	 * ShmemAlloc() won't be ready yet.  (This ordering is necessary when we
+	 * are emulating spinlocks with semaphores.)
+	 */
+	sharedSemas = (PGSemaphore)
+		ShmemAllocUnlocked(PGSemaphoreShmemSize(maxSemas));
+	numSharedSemas = 0;
+	maxSharedSemas = maxSemas;
+
+	maxSemaSets = (maxSemas + SEMAS_PER_SET - 1) / SEMAS_PER_SET;
+	mySemaSets = (IpcSemaphoreId *)
+		malloc(maxSemaSets * sizeof(IpcSemaphoreId));
+	if (mySemaSets == NULL)
+		elog(PANIC, "out of memory");
+	numSemaSets = 0;
+	nextSemaKey = statbuf.st_ino;
+	nextSemaNumber = SEMAS_PER_SET; /* force sema set alloc on 1st call */
+
+	on_shmem_exit(ReleaseSemaphores, 0);
+}
+
+/*
+ * Release semaphores at shutdown or shmem reinitialization
+ *
+ * (called as an on_shmem_exit callback, hence funny argument list)
+ */
+static void
+ReleaseSemaphores(int status, Datum arg)
+{
+	int			i;
+
+	for (i = 0; i < numSemaSets; i++)
+		IpcSemaphoreKill(mySemaSets[i]);
+	free(mySemaSets);
+}
+
+/*
+ * PGSemaphoreCreate
+ *
+ * Allocate a PGSemaphore structure with initial count 1
+ */
+PGSemaphore
+PGSemaphoreCreate(void)
+{
+	PGSemaphore sema;
+
+	/* Can't do this in a backend, because static state is postmaster's */
+	Assert(!IsUnderPostmaster);
+
+	if (nextSemaNumber >= SEMAS_PER_SET)
+	{
+		/* Time to allocate another semaphore set */
+		if (numSemaSets >= maxSemaSets)
+			elog(PANIC, "too many semaphores created");
+		mySemaSets[numSemaSets] = IpcSemaphoreCreate(SEMAS_PER_SET);
+		numSemaSets++;
+		nextSemaNumber = 0;
+	}
+	/* Use the next shared PGSemaphoreData */
+	if (numSharedSemas >= maxSharedSemas)
+		elog(PANIC, "too many semaphores created");
+	sema = &sharedSemas[numSharedSemas++];
+	/* Assign the next free semaphore in the current set */
+	sema->semId = mySemaSets[numSemaSets - 1];
+	sema->semNum = nextSemaNumber++;
+	/* Initialize it to count 1 */
+	IpcSemaphoreInitialize(sema->semId, sema->semNum, 1);
+
+	return sema;
+}
+
+/*
+ * PGSemaphoreReset
+ *
+ * Reset a previously-initialized PGSemaphore to have count 0
+ */
+void
+PGSemaphoreReset(PGSemaphore sema)
+{
+	IpcSemaphoreInitialize(sema->semId, sema->semNum, 0);
+}
+
+/*
+ * PGSemaphoreLock
+ *
+ * Lock a semaphore (decrement count), blocking if count would be < 0
+ */
+void
+PGSemaphoreLock(PGSemaphore sema)
+{
+	int			errStatus;
+	struct sembuf sops;
+
+	sops.sem_op = -1;			/* decrement */
+	sops.sem_flg = 0;
+	sops.sem_num = sema->semNum;
+
+	/*
+	 * Note: if errStatus is -1 and errno == EINTR then it means we returned
+	 * from the operation prematurely because we were sent a signal.  So we
+	 * try and lock the semaphore again.
+	 *
+	 * We used to check interrupts here, but that required servicing
+	 * interrupts directly from signal handlers. Which is hard to do safely
+	 * and portably.
+	 */
+	do
+	{
+		errStatus = semop(sema->semId, &sops, 1);
+	} while (errStatus < 0 && errno == EINTR);
+
+	if (errStatus < 0)
+		elog(FATAL, "semop(id=%d) failed: %m", sema->semId);
+}
+
+/*
+ * PGSemaphoreUnlock
+ *
+ * Unlock a semaphore (increment count)
+ */
+void
+PGSemaphoreUnlock(PGSemaphore sema)
+{
+	int			errStatus;
+	struct sembuf sops;
+
+	sops.sem_op = 1;			/* increment */
+	sops.sem_flg = 0;
+	sops.sem_num = sema->semNum;
+
+	/*
+	 * Note: if errStatus is -1 and errno == EINTR then it means we returned
+	 * from the operation prematurely because we were sent a signal.  So we
+	 * try and unlock the semaphore again. Not clear this can really happen,
+	 * but might as well cope.
+	 */
+	do
+	{
+		errStatus = semop(sema->semId, &sops, 1);
+	} while (errStatus < 0 && errno == EINTR);
+
+	if (errStatus < 0)
+		elog(FATAL, "semop(id=%d) failed: %m", sema->semId);
+}
+
+/*
+ * PGSemaphoreTryLock
+ *
+ * Lock a semaphore only if able to do so without blocking
+ */
+bool
+PGSemaphoreTryLock(PGSemaphore sema)
+{
+	int			errStatus;
+	struct sembuf sops;
+
+	sops.sem_op = -1;			/* decrement */
+	sops.sem_flg = IPC_NOWAIT;	/* but don't block */
+	sops.sem_num = sema->semNum;
+
+	/*
+	 * Note: if errStatus is -1 and errno == EINTR then it means we returned
+	 * from the operation prematurely because we were sent a signal.  So we
+	 * try and lock the semaphore again.
+	 */
+	do
+	{
+		errStatus = semop(sema->semId, &sops, 1);
+	} while (errStatus < 0 && errno == EINTR);
+
+	if (errStatus < 0)
+	{
+		/* Expect EAGAIN or EWOULDBLOCK (platform-dependent) */
+#ifdef EAGAIN
+		if (errno == EAGAIN)
+			return false;		/* failed to lock it */
+#endif
+#if defined(EWOULDBLOCK) && (!defined(EAGAIN) || (EWOULDBLOCK != EAGAIN))
+		if (errno == EWOULDBLOCK)
+			return false;		/* failed to lock it */
+#endif
+		/* Otherwise we got trouble */
+		elog(FATAL, "semop(id=%d) failed: %m", sema->semId);
+	}
+
+	return true;
+}