From: Robert Haas Date: Thu, 5 Jan 2017 17:27:09 +0000 (-0500) Subject: Fix possible crash reading pg_stat_activity. X-Git-Tag: REL_10_BETA1~1149 X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=175ff6598e014b2fe84c06fa443161294fc2eed0;p=postgresql Fix possible crash reading pg_stat_activity. With the old code, a backend that read pg_stat_activity without ever having executed a parallel query might see a backend in the midst of executing one waiting on a DSA LWLock, resulting in a crash. The solution is for backends to register the tranche at startup time, not the first time a parallel query is executed. Report by Andreas Seltenreich. Patch by me, reviewed by Thomas Munro. --- diff --git a/src/backend/executor/execParallel.c b/src/backend/executor/execParallel.c index 821f3e9a97..86d9fb59ba 100644 --- a/src/backend/executor/execParallel.c +++ b/src/backend/executor/execParallel.c @@ -486,7 +486,6 @@ ExecInitParallelPlan(PlanState *planstate, EState *estate, int nworkers) shm_toc_insert(pcxt->toc, PARALLEL_KEY_DSA, area_space); pei->area = dsa_create_in_place(area_space, dsa_minsize, LWTRANCHE_PARALLEL_QUERY_DSA, - "parallel_query_dsa", pcxt->seg); } diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c index f4be4b4a7a..1cf06848bb 100644 --- a/src/backend/storage/lmgr/lwlock.c +++ b/src/backend/storage/lmgr/lwlock.c @@ -508,6 +508,8 @@ RegisterLWLockTranches(void) LWLockRegisterTranche(LWTRANCHE_LOCK_MANAGER, "lock_manager"); LWLockRegisterTranche(LWTRANCHE_PREDICATE_LOCK_MANAGER, "predicate_lock_manager"); + LWLockRegisterTranche(LWTRANCHE_PARALLEL_QUERY_DSA, + "parallel_query_dsa"); /* Register named tranches. */ for (i = 0; i < NamedLWLockTrancheRequests; i++) diff --git a/src/backend/utils/mmgr/dsa.c b/src/backend/utils/mmgr/dsa.c index 200749feaa..2503aa5e98 100644 --- a/src/backend/utils/mmgr/dsa.c +++ b/src/backend/utils/mmgr/dsa.c @@ -276,11 +276,6 @@ static char dsa_size_class_map[] = { */ #define DSA_FULLNESS_CLASSES 4 -/* - * Maximum length of a DSA name. - */ -#define DSA_MAXLEN 64 - /* * A dsa_area_pool represents a set of objects of a given size class. * @@ -326,7 +321,6 @@ typedef struct Size freed_segment_counter; /* The LWLock tranche ID. */ int lwlock_tranche_id; - char lwlock_tranche_name[DSA_MAXLEN]; /* The general lock (protects everything except object pools). */ LWLock lock; } dsa_area_control; @@ -405,7 +399,7 @@ static void unlink_segment(dsa_area *area, dsa_segment_map *segment_map); static dsa_segment_map *get_best_segment(dsa_area *area, Size npages); static dsa_segment_map *make_new_segment(dsa_area *area, Size requested_pages); static dsa_area *create_internal(void *place, size_t size, - int tranche_id, const char *tranche_name, + int tranche_id, dsm_handle control_handle, dsm_segment *control_segment); static dsa_area *attach_internal(void *place, dsm_segment *segment, @@ -419,12 +413,10 @@ static void check_for_freed_segments(dsa_area *area); * We can't allocate a LWLock tranche_id within this function, because tranche * IDs are a scarce resource; there are only 64k available, using low numbers * when possible matters, and we have no provision for recycling them. So, - * we require the caller to provide one. The caller must also provide the - * tranche name, so that we can distinguish LWLocks belonging to different - * DSAs. + * we require the caller to provide one. */ dsa_area * -dsa_create(int tranche_id, const char *tranche_name) +dsa_create(int tranche_id) { dsm_segment *segment; dsa_area *area; @@ -446,7 +438,7 @@ dsa_create(int tranche_id, const char *tranche_name) /* Create a new DSA area with the control objet in this segment. */ area = create_internal(dsm_segment_address(segment), DSA_INITIAL_SEGMENT_SIZE, - tranche_id, tranche_name, + tranche_id, dsm_segment_handle(segment), segment); /* Clean up when the control segment detaches. */ @@ -474,12 +466,11 @@ dsa_create(int tranche_id, const char *tranche_name) */ dsa_area * dsa_create_in_place(void *place, size_t size, - int tranche_id, const char *tranche_name, - dsm_segment *segment) + int tranche_id, dsm_segment *segment) { dsa_area *area; - area = create_internal(place, size, tranche_id, tranche_name, + area = create_internal(place, size, tranche_id, DSM_HANDLE_INVALID, NULL); /* @@ -1139,7 +1130,7 @@ dsa_minimum_size(void) */ static dsa_area * create_internal(void *place, size_t size, - int tranche_id, const char *tranche_name, + int tranche_id, dsm_handle control_handle, dsm_segment *control_segment) { @@ -1192,7 +1183,6 @@ create_internal(void *place, size_t size, control->refcnt = 1; control->freed_segment_counter = 0; control->lwlock_tranche_id = tranche_id; - strlcpy(control->lwlock_tranche_name, tranche_name, DSA_MAXLEN); /* * Create the dsa_area object that this backend will use to access the @@ -1204,8 +1194,6 @@ create_internal(void *place, size_t size, area->mapping_pinned = false; memset(area->segment_maps, 0, sizeof(dsa_segment_map) * DSA_MAX_SEGMENTS); area->high_segment_index = 0; - LWLockRegisterTranche(control->lwlock_tranche_id, - control->lwlock_tranche_name); LWLockInitialize(&control->lock, control->lwlock_tranche_id); for (i = 0; i < DSA_NUM_SIZE_CLASSES; ++i) LWLockInitialize(DSA_SCLASS_LOCK(area, i), @@ -1262,8 +1250,6 @@ attach_internal(void *place, dsm_segment *segment, dsa_handle handle) memset(&area->segment_maps[0], 0, sizeof(dsa_segment_map) * DSA_MAX_SEGMENTS); area->high_segment_index = 0; - LWLockRegisterTranche(control->lwlock_tranche_id, - control->lwlock_tranche_name); /* Set up the segment map for this process's mapping. */ segment_map = &area->segment_maps[0]; diff --git a/src/include/utils/dsa.h b/src/include/utils/dsa.h index 0aca58f529..bb634e77cd 100644 --- a/src/include/utils/dsa.h +++ b/src/include/utils/dsa.h @@ -90,10 +90,9 @@ typedef dsm_handle dsa_handle; extern void dsa_startup(void); -extern dsa_area *dsa_create(int tranche_id, const char *tranche_name); +extern dsa_area *dsa_create(int tranche_id); extern dsa_area *dsa_create_in_place(void *place, Size size, - int tranche_id, const char *tranche_name, - dsm_segment *segment); + int tranche_id, dsm_segment *segment); extern dsa_area *dsa_attach(dsa_handle handle); extern dsa_area *dsa_attach_in_place(void *place, dsm_segment *segment); extern void dsa_release_in_place(void *place);