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bcachefs: fix incorrect usage of REQ_OP_FLUSH

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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>
This commit is contained in:
Christoph Hellwig 2024-01-11 08:36:55 +01:00 committed by Kent Overstreet
parent 612e1110d6
commit 3e44f325f6
2 changed files with 3 additions and 2 deletions
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2
fs/bcachefs/fs-io.c
View File

@ -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);

3
fs/bcachefs/journal_io.c
View File

@ -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);