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Commite17ab38

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committed
[refer #PGPRO-6599]: Avoid race conditions while processing PROFILE_REQUEST and
PROFILE_RESET requests.After initialization of "request" variable in collector.c main loop anotherclient backend could change the value of "collector_hdr->request" variable.Changing this value from "PROFILE_RESET" to "PROFILE_REQUEST" could causedeadlock: "collector" processed "PROFILE_RESET" query while client backendwaits data from the "collector_mq" shared memory message queue. Now we readand write "collector_hdr->request" variable only using "PGWS_COLLECTOR_LOCK"lock.Removed obsolete "read_current_wait()" function definition frompg_wait_sampling.h.tags: pg_wait_sampling
1 parentaf53205 commite17ab38

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3 files changed

+10
-11
lines changed

3 files changed

+10
-11
lines changed

‎collector.c‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -446,11 +446,12 @@ collector_main(Datum main_arg)
446446
if (collector_hdr->request!=NO_REQUEST)
447447
{
448448
LOCKTAGtag;
449-
SHMRequestrequest=collector_hdr->request;
449+
SHMRequestrequest;
450450

451451
init_lock_tag(&tag,PGWS_COLLECTOR_LOCK);
452452

453453
LockAcquire(&tag,ExclusiveLock, false, false);
454+
request=collector_hdr->request;
454455
collector_hdr->request=NO_REQUEST;
455456

456457
if (request==HISTORY_REQUEST||request==PROFILE_REQUEST)

‎pg_wait_sampling.c‎

Lines changed: 8 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -590,13 +590,12 @@ receive_array(SHMRequest request, Size item_size, Size *count)
590590
init_lock_tag(&queueTag,PGWS_QUEUE_LOCK);
591591
LockAcquire(&queueTag,ExclusiveLock, false, false);
592592

593-
/* Ensure collector has processed previous request */
593+
recv_mq=shm_mq_create(collector_mq,COLLECTOR_QUEUE_SIZE);
594+
594595
init_lock_tag(&collectorTag,PGWS_COLLECTOR_LOCK);
595596
LockAcquire(&collectorTag,ExclusiveLock, false, false);
596-
LockRelease(&collectorTag,ExclusiveLock, false);
597-
598-
recv_mq=shm_mq_create(collector_mq,COLLECTOR_QUEUE_SIZE);
599597
collector_hdr->request=request;
598+
LockRelease(&collectorTag,ExclusiveLock, false);
600599

601600
if (!collector_hdr->latch)
602601
ereport(ERROR, (errcode(ERRCODE_INTERNAL_ERROR),
@@ -756,19 +755,19 @@ Datum
756755
pg_wait_sampling_reset_profile(PG_FUNCTION_ARGS)
757756
{
758757
LOCKTAGtag;
759-
LOCKTAGtagCollector;
758+
LOCKTAGcollectorTag;
760759

761760
check_shmem();
762761

763762
init_lock_tag(&tag,PGWS_QUEUE_LOCK);
764763

765764
LockAcquire(&tag,ExclusiveLock, false, false);
766765

767-
init_lock_tag(&tagCollector,PGWS_COLLECTOR_LOCK);
768-
LockAcquire(&tagCollector,ExclusiveLock, false, false);
769-
LockRelease(&tagCollector,ExclusiveLock, false);
770-
766+
init_lock_tag(&collectorTag,PGWS_COLLECTOR_LOCK);
767+
LockAcquire(&collectorTag,ExclusiveLock, false, false);
771768
collector_hdr->request=PROFILE_RESET;
769+
LockRelease(&collectorTag,ExclusiveLock, false);
770+
772771
SetLatch(collector_hdr->latch);
773772

774773
LockRelease(&tag,ExclusiveLock, false);

‎pg_wait_sampling.h‎

Lines changed: 0 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -75,7 +75,6 @@ extern void check_shmem(void);
7575
externCollectorShmqHeader*collector_hdr;
7676
externshm_mq*collector_mq;
7777
externuint64*proc_queryids;
78-
externvoidread_current_wait(PGPROC*proc,HistoryItem*item);
7978
externvoidinit_lock_tag(LOCKTAG*tag,uint32lock);
8079

8180
/* collector.c */

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