From d86d20f0ba79451f19782dbb5fbf206746aaffd1 Mon Sep 17 00:00:00 2001 From: Michael Paquier Date: Mon, 22 Jan 2024 10:15:50 +0900 Subject: Add backend support for injection points MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection points are a new facility that makes possible for developers to run custom code in pre-defined code paths. Its goal is to provide ways to design and run advanced tests, for cases like: - Race conditions, where processes need to do actions in a controlled ordered manner. - Forcing a state, like an ERROR, FATAL or even PANIC for OOM, to force recovery, etc. - Arbitrary sleeps. This implements some basics, and there are plans to extend it more in the future depending on what's required. Hence, this commit adds a set of routines in the backend that allows developers to attach, detach and run injection points: - A code path calling an injection point can be declared with the macro INJECTION_POINT(name). - InjectionPointAttach() and InjectionPointDetach() to respectively attach and detach a callback to/from an injection point. An injection point name is registered in a shmem hash table with a library name and a function name, which will be used to load the callback attached to an injection point when its code path is run. Injection point names are just strings, so as an injection point can be declared and run by out-of-core extensions and modules, with callbacks defined in external libraries. This facility is hidden behind a dedicated switch for ./configure and meson, disabled by default. Note that backends use a local cache to store callbacks already loaded, cleaning up their cache if a callback has found to be removed on a best-effort basis. This could be refined further but any tests but what we have here was fine with the tests I've written while implementing these backend APIs. Author: Michael Paquier, with doc suggestions from Ashutosh Bapat. Reviewed-by: Ashutosh Bapat, Nathan Bossart, Álvaro Herrera, Dilip Kumar, Amul Sul, Nazir Bilal Yavuz Discussion: https://postgr.es/m/ZTiV8tn_MIb_H2rE@paquier.xyz --- src/backend/utils/misc/injection_point.c | 317 +++++++++++++++++++++++++++++++ 1 file changed, 317 insertions(+) create mode 100644 src/backend/utils/misc/injection_point.c (limited to 'src/backend/utils/misc/injection_point.c') diff --git a/src/backend/utils/misc/injection_point.c b/src/backend/utils/misc/injection_point.c new file mode 100644 index 00000000000..a4ee00559b3 --- /dev/null +++ b/src/backend/utils/misc/injection_point.c @@ -0,0 +1,317 @@ +/*------------------------------------------------------------------------- + * + * injection_point.c + * Routines to control and run injection points in the code. + * + * Injection points can be used to run arbitrary code by attaching callbacks + * that would be executed in place of the named injection point. + * + * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group + * Portions Copyright (c) 1994, Regents of the University of California + * + * + * IDENTIFICATION + * src/backend/utils/misc/injection_point.c + * + *------------------------------------------------------------------------- + */ +#include "postgres.h" + +#include + +#include "fmgr.h" +#include "miscadmin.h" +#include "port/pg_bitutils.h" +#include "storage/fd.h" +#include "storage/lwlock.h" +#include "storage/shmem.h" +#include "utils/hsearch.h" +#include "utils/injection_point.h" +#include "utils/memutils.h" + +#ifdef USE_INJECTION_POINTS + +/* + * Hash table for storing injection points. + * + * InjectionPointHash is used to find an injection point by name. + */ +static HTAB *InjectionPointHash; /* find points from names */ + +/* Field sizes */ +#define INJ_NAME_MAXLEN 64 +#define INJ_LIB_MAXLEN 128 +#define INJ_FUNC_MAXLEN 128 + +/* Single injection point stored in InjectionPointHash */ +typedef struct InjectionPointEntry +{ + char name[INJ_NAME_MAXLEN]; /* hash key */ + char library[INJ_LIB_MAXLEN]; /* library */ + char function[INJ_FUNC_MAXLEN]; /* function */ +} InjectionPointEntry; + +#define INJECTION_POINT_HASH_INIT_SIZE 16 +#define INJECTION_POINT_HASH_MAX_SIZE 128 + +/* + * Backend local cache of injection callbacks already loaded, stored in + * TopMemoryContext. + */ +typedef struct InjectionPointCacheEntry +{ + char name[INJ_NAME_MAXLEN]; + InjectionPointCallback callback; +} InjectionPointCacheEntry; + +static HTAB *InjectionPointCache = NULL; + +/* + * injection_point_cache_add + * + * Add an injection point to the local cache. + */ +static void +injection_point_cache_add(const char *name, + InjectionPointCallback callback) +{ + InjectionPointCacheEntry *entry; + bool found; + + /* If first time, initialize */ + if (InjectionPointCache == NULL) + { + HASHCTL hash_ctl; + + hash_ctl.keysize = sizeof(char[INJ_NAME_MAXLEN]); + hash_ctl.entrysize = sizeof(InjectionPointCacheEntry); + hash_ctl.hcxt = TopMemoryContext; + + InjectionPointCache = hash_create("InjectionPoint cache hash", + INJECTION_POINT_HASH_MAX_SIZE, + &hash_ctl, + HASH_ELEM | HASH_STRINGS | HASH_CONTEXT); + } + + entry = (InjectionPointCacheEntry *) + hash_search(InjectionPointCache, name, HASH_ENTER, &found); + + Assert(!found); + memcpy(entry->name, name, strlen(name)); + entry->callback = callback; +} + +/* + * injection_point_cache_remove + * + * Remove entry from the local cache. Note that this leaks a callback + * loaded but removed later on, which should have no consequence from + * a testing perspective. + */ +static void +injection_point_cache_remove(const char *name) +{ + /* leave if no cache */ + if (InjectionPointCache == NULL) + return; + + (void) hash_search(InjectionPointCache, name, HASH_REMOVE, NULL); +} + +/* + * injection_point_cache_get + * + * Retrieve an injection point from the local cache, if any. + */ +static InjectionPointCallback +injection_point_cache_get(const char *name) +{ + bool found; + InjectionPointCacheEntry *entry; + + /* no callback if no cache yet */ + if (InjectionPointCache == NULL) + return NULL; + + entry = (InjectionPointCacheEntry *) + hash_search(InjectionPointCache, name, HASH_FIND, &found); + + if (found) + return entry->callback; + + return NULL; +} +#endif /* USE_INJECTION_POINTS */ + +/* + * Return the space for dynamic shared hash table. + */ +Size +InjectionPointShmemSize(void) +{ +#ifdef USE_INJECTION_POINTS + Size sz = 0; + + sz = add_size(sz, hash_estimate_size(INJECTION_POINT_HASH_MAX_SIZE, + sizeof(InjectionPointEntry))); + return sz; +#else + return 0; +#endif +} + +/* + * Allocate shmem space for dynamic shared hash. + */ +void +InjectionPointShmemInit(void) +{ +#ifdef USE_INJECTION_POINTS + HASHCTL info; + + /* key is a NULL-terminated string */ + info.keysize = sizeof(char[INJ_NAME_MAXLEN]); + info.entrysize = sizeof(InjectionPointEntry); + InjectionPointHash = ShmemInitHash("InjectionPoint hash", + INJECTION_POINT_HASH_INIT_SIZE, + INJECTION_POINT_HASH_MAX_SIZE, + &info, + HASH_ELEM | HASH_FIXED_SIZE | HASH_STRINGS); +#endif +} + +/* + * Attach a new injection point. + */ +void +InjectionPointAttach(const char *name, + const char *library, + const char *function) +{ +#ifdef USE_INJECTION_POINTS + InjectionPointEntry *entry_by_name; + bool found; + + if (strlen(name) >= INJ_NAME_MAXLEN) + elog(ERROR, "injection point name %s too long (maximum of %u)", + name, INJ_NAME_MAXLEN); + if (strlen(library) >= INJ_LIB_MAXLEN) + elog(ERROR, "injection point library %s too long (maximum of %u)", + library, INJ_LIB_MAXLEN); + if (strlen(function) >= INJ_FUNC_MAXLEN) + elog(ERROR, "injection point function %s too long (maximum of %u)", + function, INJ_FUNC_MAXLEN); + + /* + * Allocate and register a new injection point. A new point should not + * exist. For testing purposes this should be fine. + */ + LWLockAcquire(InjectionPointLock, LW_EXCLUSIVE); + entry_by_name = (InjectionPointEntry *) + hash_search(InjectionPointHash, name, + HASH_ENTER, &found); + if (found) + { + LWLockRelease(InjectionPointLock); + elog(ERROR, "injection point \"%s\" already defined", name); + } + + /* Save the entry */ + memcpy(entry_by_name->name, name, sizeof(entry_by_name->name)); + entry_by_name->name[INJ_NAME_MAXLEN - 1] = '\0'; + memcpy(entry_by_name->library, library, sizeof(entry_by_name->library)); + entry_by_name->library[INJ_LIB_MAXLEN - 1] = '\0'; + memcpy(entry_by_name->function, function, sizeof(entry_by_name->function)); + entry_by_name->function[INJ_FUNC_MAXLEN - 1] = '\0'; + + LWLockRelease(InjectionPointLock); + +#else + elog(ERROR, "injection points are not supported by this build"); +#endif +} + +/* + * Detach an existing injection point. + */ +void +InjectionPointDetach(const char *name) +{ +#ifdef USE_INJECTION_POINTS + bool found; + + LWLockAcquire(InjectionPointLock, LW_EXCLUSIVE); + hash_search(InjectionPointHash, name, HASH_REMOVE, &found); + LWLockRelease(InjectionPointLock); + + if (!found) + elog(ERROR, "injection point \"%s\" not found", name); + +#else + elog(ERROR, "Injection points are not supported by this build"); +#endif +} + +/* + * Execute an injection point, if defined. + * + * Check first the shared hash table, and adapt the local cache depending + * on that as it could be possible that an entry to run has been removed. + */ +void +InjectionPointRun(const char *name) +{ +#ifdef USE_INJECTION_POINTS + InjectionPointEntry *entry_by_name; + bool found; + InjectionPointCallback injection_callback; + + LWLockAcquire(InjectionPointLock, LW_SHARED); + entry_by_name = (InjectionPointEntry *) + hash_search(InjectionPointHash, name, + HASH_FIND, &found); + LWLockRelease(InjectionPointLock); + + /* + * If not found, do nothing and remove it from the local cache if it + * existed there. + */ + if (!found) + { + injection_point_cache_remove(name); + return; + } + + /* + * Check if the callback exists in the local cache, to avoid unnecessary + * external loads. + */ + injection_callback = injection_point_cache_get(name); + if (injection_callback == NULL) + { + char path[MAXPGPATH]; + + /* not found in local cache, so load and register */ + snprintf(path, MAXPGPATH, "%s/%s%s", pkglib_path, + entry_by_name->library, DLSUFFIX); + + if (!pg_file_exists(path)) + elog(ERROR, "could not find library \"%s\" for injection point \"%s\"", + path, name); + + injection_callback = (InjectionPointCallback) + load_external_function(path, entry_by_name->function, true, NULL); + + if (injection_callback == NULL) + elog(ERROR, "could not find function \"%s\" in library \"%s\" for injection point \"%s\"", + name, entry_by_name->function, path); + + /* add it to the local cache when found */ + injection_point_cache_add(name, injection_callback); + } + + injection_callback(name); +#else + elog(ERROR, "Injection points are not supported by this build"); +#endif +} -- cgit v1.2.3