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>
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);
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);