bcachefs: fix incorrect usage of REQ_OP_FLUSH

REQ_OP_FLUSH is only for internal use in the blk-mq and request based
drivers. File systems and other block layer consumers must use
REQ_OP_WRITE | REQ_PREFLUSH as documented in
Documentation/block/writeback_cache_control.rst.

While REQ_OP_FLUSH appears to work for blk-mq drivers it does not
get the proper flush state machine handling, and completely fails
for any bio based drivers, including all the stacking drivers.  The
block layer will also get a check in 6.8 to reject this use case
entirely.

[Note: completely untested, but as this never got fixed since the
original bug report in November:

   https://bugzilla.kernel.org/show_bug.cgi?id=218184

and the the discussion in December:

    https://lore.kernel.org/all/20231221053016.72cqcfg46vxwohcj@moria.home.lan/T/

this seems to be best way to force it]

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

diff --git a/fs/bcachefs/fs-io.c b/fs/bcachefs/fs-io.c
index dc52918d06ef3f91c30484822a5a170b08543f9c..8c70123b6a0c809b6d50040593281c2e9c115828 100644 (file)
--- a/fs/bcachefs/fs-io.c
+++ b/fs/bcachefs/fs-io.c
@@ -79,7 +79,7 @@ void bch2_inode_flush_nocow_writes_async(struct bch_fs *c,
                        continue;
 
                bio = container_of(bio_alloc_bioset(ca->disk_sb.bdev, 0,
-                                                   REQ_OP_FLUSH,
+                                                   REQ_OP_WRITE|REQ_PREFLUSH,
                                                    GFP_KERNEL,
                                                    &c->nocow_flush_bioset),
                                   struct nocow_flush, bio);

diff --git a/fs/bcachefs/journal_io.c b/fs/bcachefs/journal_io.c
index 04a1e79a5ed392cd8ebaac922a2516b374a6d094..bfd6585e746da45880da9b5ad8fb502586cbf933 100644 (file)
--- a/fs/bcachefs/journal_io.c
+++ b/fs/bcachefs/journal_io.c
@@ -1988,7 +1988,8 @@ CLOSURE_CALLBACK(bch2_journal_write)
                        percpu_ref_get(&ca->io_ref);
 
                        bio = ca->journal.bio;
-                       bio_reset(bio, ca->disk_sb.bdev, REQ_OP_FLUSH);
+                       bio_reset(bio, ca->disk_sb.bdev,
+                                 REQ_OP_WRITE|REQ_PREFLUSH);
                        bio->bi_end_io          = journal_write_endio;
                        bio->bi_private         = ca;
                        closure_bio_submit(bio, cl);