Improve assertion in mdwritev()

michaelpq · michaelpq · commit f04d1c1db011 · 2024-06-04T07:15:10.000+09:00
The assertion used at the beginning of mdwritev(), that is not enabled except by defining -DCHECK_WRITE_VS_EXTEND as mdnblocks() is costly, forgot about the total number of blocks to write at location specified by the caller. The calculation is fixed to count for that, and uses casts to uint64 to ensure a proper check should the number of blocks overflow. Using a cast is a suggestion from Tom Lane. Oversight in 4908c58. Author: Xing Guo Discussion: https://postgr.es/m/CACpMh+BM-VgKeO7suPG-VHTtpzJ+zsbDPwVHu42PLp-iTk0z+A@mail.gmail.com
diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c
@@ -930,7 +930,7 @@ mdwritev(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
 {
 	/* This assert is too expensive to have on normally ... */
 #ifdef CHECK_WRITE_VS_EXTEND
-	Assert(blocknum < mdnblocks(reln, forknum));
+	Assert((uint64) blocknum + (uint64) nblocks <= (uint64) mdnblocks(reln, forknum));
 #endif
 
 	while (nblocks > 0)

Original file line number	Diff line number	Diff line change
`@@ -930,7 +930,7 @@ mdwritev(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,`
`930`	`930`	`{`
`931`	`931`	`/* This assert is too expensive to have on normally ... */`
`932`	`932`	`#ifdef CHECK_WRITE_VS_EXTEND`
`933`		`- Assert(blocknum < mdnblocks(reln, forknum));`
	`933`	`+ Assert((uint64) blocknum + (uint64) nblocks <= (uint64) mdnblocks(reln, forknum));`
`934`	`934`	`#endif`
`935`	`935`
`936`	`936`	`while (nblocks > 0)`