dm: don't use bio_trim() afterall

snitm · snitm · commit fa8db4948f52 · 2019-02-06T17:24:37.000-05:00
bio_trim() has an early return, which makes it _not_ idempotent, if the offset is 0 and the bio's bi_size already matches the requested size. Prior to DM, all users of bio_trim() were fine with this. But DM has exposed the fact that bio_trim()'s early return is incompatible with a cloned bio whose integrity payload must be trimmed via bio_integrity_trim(). Fix this by reverting DM back to doing the equivalent of bio_trim() but in an idempotent manner (so bio_integrity_trim is always performed). Follow-on work is needed to assess what benefit bio_trim()'s early return is providing to its existing callers. Reported-by: Milan Broz <gmazyland@gmail.com> Fixes: 57c3651 ("dm: fix clone_bio() to trigger blk_recount_segments()") Signed-off-by: Mike Snitzer <snitzer@redhat.com>
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
@@ -1336,7 +1336,11 @@ static int clone_bio(struct dm_target_io *tio, struct bio *bio,
 			return r;
 	}
 
-	bio_trim(clone, sector - clone->bi_iter.bi_sector, len);
+	bio_advance(clone, to_bytes(sector - clone->bi_iter.bi_sector));
+	clone->bi_iter.bi_size = to_bytes(len);
+
+	if (bio_integrity(bio))
+		bio_integrity_trim(clone);
 
 	return 0;
 }

Original file line number	Diff line number	Diff line change
`@@ -1336,7 +1336,11 @@ static int clone_bio(struct dm_target_io tio, struct bio bio,`
`1336`	`1336`	`return r;`
`1337`	`1337`	`}`
`1338`	`1338`
`1339`		`- bio_trim(clone, sector - clone->bi_iter.bi_sector, len);`
	`1339`	`+ bio_advance(clone, to_bytes(sector - clone->bi_iter.bi_sector));`
	`1340`	`+ clone->bi_iter.bi_size = to_bytes(len);`
	`1341`	`+`
	`1342`	`+ if (bio_integrity(bio))`
	`1343`	`+ bio_integrity_trim(clone);`
`1340`	`1344`
`1341`	`1345`	`return 0;`
`1342`	`1346`	`}`