pgstat: prevent fix pgstat_reinit_entry() from zeroing out lwlock.

anarazel · anarazel · commit 81ae9e658874 · 2022-04-06T23:35:56.000-07:00
Zeroing out an lwlock in a normal build turns out to not trigger any alarms,
if nobody can use the lwlock at that moment (as the case here). But with
--disable-spinlocks --disable-atomics, the sema field needs to be initialized.

We probably should make sure that this fails on more common configurations as
well...

Per buildfarm animal rorqual
diff --git a/src/backend/utils/activity/pgstat_shmem.c b/src/backend/utils/activity/pgstat_shmem.c
@@ -292,8 +292,8 @@ pgstat_reinit_entry(PgStat_Kind kind, PgStatShared_HashEntry *shhashent)
 
 	/* reinitialize content */
 	Assert(shheader->magic == 0xdeadbeef);
-	memset(shheader, 0, pgstat_get_kind_info(shhashent->key.kind)->shared_size);
-	shheader->magic = 0xdeadbeef;
+	memset(pgstat_get_entry_data(kind, shheader), 0,
+		   pgstat_get_entry_len(kind));
 
 	return shheader;
 }

Original file line number	Diff line number	Diff line change
`@@ -292,8 +292,8 @@ pgstat_reinit_entry(PgStat_Kind kind, PgStatShared_HashEntry *shhashent)`
`292`	`292`
`293`	`293`	`/* reinitialize content */`
`294`	`294`	`Assert(shheader->magic == 0xdeadbeef);`
`295`		`- memset(shheader, 0, pgstat_get_kind_info(shhashent->key.kind)->shared_size);`
`296`		`- shheader->magic = 0xdeadbeef;`
	`295`	`+ memset(pgstat_get_entry_data(kind, shheader), 0,`
	`296`	`+ pgstat_get_entry_len(kind));`
`297`	`297`
`298`	`298`	`return shheader;`
`299`	`299`	`}`