Fix calculation of how much shared memory is required to store a TOC.

MasaoFujii · MasaoFujii · commit 2ad78a87f018 · 2021-01-15T12:44:17.000+09:00
Commit ac883ac refactored shm_toc_estimate() but changed its calculation of shared memory size for TOC incorrectly. Previously this could cause too large memory to be allocated. Back-patch to v11 where the bug was introduced. Author: Takayuki Tsunakawa Discussion: https://postgr.es/m/TYAPR01MB2990BFB73170E2C4921E2C4DFEA80@TYAPR01MB2990.jpnprd01.prod.outlook.com
diff --git a/src/backend/storage/ipc/shm_toc.c b/src/backend/storage/ipc/shm_toc.c
@@ -265,8 +265,8 @@ shm_toc_estimate(shm_toc_estimator *e)
 	Size		sz;
 
 	sz = offsetof(shm_toc, toc_entry);
-	sz += add_size(sz, mul_size(e->number_of_keys, sizeof(shm_toc_entry)));
-	sz += add_size(sz, e->space_for_chunks);
+	sz = add_size(sz, mul_size(e->number_of_keys, sizeof(shm_toc_entry)));
+	sz = add_size(sz, e->space_for_chunks);
 
 	return BUFFERALIGN(sz);
 }

Original file line number	Diff line number	Diff line change
`@@ -265,8 +265,8 @@ shm_toc_estimate(shm_toc_estimator *e)`
`265`	`265`	`Size sz;`
`266`	`266`
`267`	`267`	`sz = offsetof(shm_toc, toc_entry);`
`268`		`- sz += add_size(sz, mul_size(e->number_of_keys, sizeof(shm_toc_entry)));`
`269`		`- sz += add_size(sz, e->space_for_chunks);`
	`268`	`+ sz = add_size(sz, mul_size(e->number_of_keys, sizeof(shm_toc_entry)));`
	`269`	`+ sz = add_size(sz, e->space_for_chunks);`
`270`	`270`
`271`	`271`	`return BUFFERALIGN(sz);`
`272`	`272`	`}`