Commit 3e44f325 authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Kent Overstreet
Browse files

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: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarKent Overstreet <kent.overstreet@linux.dev>
parent 612e1110

fs/bcachefs/fs-io.c

+1 −1
Original line number Diff line number Diff line
@@ -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);

fs/bcachefs/journal_io.c

+2 −1
Original line number Diff line number Diff line
@@ -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);