bcache: Fix flushes in writeback mode

In writeback mode, when we get a cache flush we need to make sure we
issue a flush to the backing device.

The code for sending down an extra flush was wrong - by cloning the bio
we were probably getting flags that didn't make sense for a bare flush,
and also the old code was firing for FUA bios, for which we don't need
to send a flush to the backing device.

This was causing data corruption somehow - the mechanism was never
determined, but this patch fixes it for the users that were seeing it.

Signed-off-by: Kent Overstreet <kmo@daterainc.com>
Cc: linux-stable <stable@vger.kernel.org> # >= v3.10
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 9 insertions, 6 deletions

diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
index 786a1a4f74d8..71eb233b9ace 100644
--- a/drivers/md/bcache/request.c
+++ b/drivers/md/bcache/request.c
@@ -997,14 +997,17 @@ static void request_write(struct cached_dev *dc, struct search *s)
         } else {
                 bch_writeback_add(dc);
 
-                if (s->op.flush_journal) {
+                if (bio->bi_rw & REQ_FLUSH) {
                         /* Also need to send a flush to the backing device */
-                        s->op.cache_bio = bio_clone_bioset(bio, GFP_NOIO,
-                                                           dc->disk.bio_split);
+                        struct bio *flush = bio_alloc_bioset(0, GFP_NOIO,
+                                                             dc->disk.bio_split);
 
-                        bio->bi_size = 0;
-                        bio->bi_vcnt = 0;
-                        closure_bio_submit(bio, cl, s->d);
+                        flush->bi_rw    = WRITE_FLUSH;
+                        flush->bi_bdev  = bio->bi_bdev;
+                        flush->bi_end_io = request_endio;
+                        flush->bi_private = cl;
+
+                        closure_bio_submit(flush, cl, s->d);
                 } else {
                         s->op.cache_bio = bio;
                 }