[dm-devel] [PATCH] dm-thinp: fix REQ_FLUSH semantics

[Christoph Hellwig]

REQ_FLUSH means the metadata needs to be flushed before the data payload
(if there is one), not after it.  And yes, this means the typical
REQ_FUA|REQ_FLUSH requests imply two flushes.

Signed-off-by: Christoph Hellwig <hch at lst.de>

Index: linux-2.6/drivers/md/dm-thin-prov.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-thin-prov.c	2011-04-27 11:45:50.957995412 +0200
+++ linux-2.6/drivers/md/dm-thin-prov.c	2011-04-27 11:45:56.954629592 +0200
@@ -229,6 +229,14 @@ static void do_bios(struct thinp_c *tc,
 	block_t thinp_block, pool_block;
 
 	while ((bio = bio_list_pop(bios))) {
+		if (bio->bi_rw & REQ_FLUSH) {
+			r = commit(tc);
+			if (r < 0) {
+				bio_io_error(bio);
+				continue;
+			}
+		}
+
 		thinp_block = _sector_to_block(tc, bio->bi_sector);
 		r = thinp_metadata_lookup(tc->tpm, thinp_block, 1, &pool_block);
 		if (r == -ENODATA) {
@@ -258,7 +266,7 @@ static void do_bios(struct thinp_c *tc,
 			 * whether the overhead of tracking pending blocks
 			 * is worth it though.
 			 */
-			if ((bio->bi_rw & (REQ_FUA | REQ_FLUSH))) {
+			if (bio->bi_rw & REQ_FUA) {
 				r = commit(tc);
 				if (r < 0) {
 					bio_io_error(bio);