Fix using injection points at backend startup in EXEC_BACKEND mode

Commit 86db52a changed the locking of injection points to use only
atomic ops and spinlocks, to make it possible to define injection
points in processes that don't have a PGPROC entry (yet). However, it
didn't work in EXEC_BACKEND mode, because the pointer to shared memory
area was not initialized until the process "attaches" to all the
shared memory structs. To fix, pass the pointer to the child process
along with other global variables that need to be set up early.

Backpatch-through: 17

Author: hlinnaka

src/backend/postmaster/launch_backend.c

@@ -63,6 +63,7 @@
 #include "utils/builtins.h"
 #include "utils/datetime.h"
 #include "utils/guc.h"
+#include "utils/injection_point.h"
 #include "utils/memutils.h"
 #include "utils/timestamp.h"
 
@@ -104,6 +105,9 @@ typedef struct
 	void	   *UsedShmemSegAddr;
 	slock_t    *ShmemLock;
 	struct bkend *ShmemBackendArray;
+#ifdef USE_INJECTION_POINTS
+	struct InjectionPointsCtl *ActiveInjectionPoints;
+#endif
 #ifndef HAVE_SPINLOCKS
 	PGSemaphore *SpinlockSemaArray;
 #endif
@@ -710,6 +714,10 @@ save_backend_variables(BackendParameters *param, ClientSocket *client_sock,
 	param->ShmemLock = ShmemLock;
 	param->ShmemBackendArray = ShmemBackendArray;
 
+#ifdef USE_INJECTION_POINTS
+	param->ActiveInjectionPoints = ActiveInjectionPoints;
+#endif
+
 #ifndef HAVE_SPINLOCKS
 	param->SpinlockSemaArray = SpinlockSemaArray;
 #endif
@@ -969,6 +977,10 @@ restore_backend_variables(BackendParameters *param)
 	ShmemLock = param->ShmemLock;
 	ShmemBackendArray = param->ShmemBackendArray;
 
+#ifdef USE_INJECTION_POINTS
+	ActiveInjectionPoints = param->ActiveInjectionPoints;
+#endif
+
 #ifndef HAVE_SPINLOCKS
 	SpinlockSemaArray = param->SpinlockSemaArray;
 #endif

src/backend/utils/misc/injection_point.c

@@ -85,7 +85,7 @@ typedef struct InjectionPointsCtl
 	InjectionPointEntry entries[MAX_INJECTION_POINTS];
 } InjectionPointsCtl;
 
-static InjectionPointsCtl *ActiveInjectionPoints;
+NON_EXEC_STATIC InjectionPointsCtl *ActiveInjectionPoints;
 
 /*
  * Backend local cache of injection callbacks already loaded, stored in

src/include/utils/injection_point.h

@@ -43,4 +43,8 @@ extern void InjectionPointRun(const char *name);
 extern void InjectionPointCached(const char *name);
 extern bool InjectionPointDetach(const char *name);
 
+#ifdef EXEC_BACKEND
+extern PGDLLIMPORT struct InjectionPointsCtl *ActiveInjectionPoints;
+#endif
+
 #endif							/* INJECTION_POINT_H */