The read side is already covered as btrfs uses the generic filemap
helpers. For writes, just pass in FGP_UNCACHED if uncached IO is being
done, then the folios created should be marked appropriately.

For IO completion, ensure that writing back folios that are uncached
gets punted to one of the btrfs workers, as task context is needed for
that. Add an 'uncached_io' member to struct btrfs_bio to manage that.

With that, add FOP_UNCACHED to the btrfs file_operations fop_flags
structure, enabling use of RWF_UNCACHED.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/btrfs/bio.c       | 4 ++--
 fs/btrfs/bio.h       | 2 ++
 fs/btrfs/extent_io.c | 8 +++++++-
 fs/btrfs/file.c      | 9 ++++++---
 4 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/fs/btrfs/bio.c b/fs/btrfs/bio.c
index 7e0f9600b80c..253e1a656934 100644
--- a/fs/btrfs/bio.c
+++ b/fs/btrfs/bio.c
@@ -334,7 +334,7 @@ static void btrfs_end_bio_work(struct work_struct *work)
 	struct btrfs_bio *bbio = container_of(work, struct btrfs_bio, end_io_work);
 
 	/* Metadata reads are checked and repaired by the submitter. */
-	if (is_data_bbio(bbio))
+	if (bio_op(&bbio->bio) == REQ_OP_READ && is_data_bbio(bbio))
 		btrfs_check_read_bio(bbio, bbio->bio.bi_private);
 	else
 		btrfs_bio_end_io(bbio, bbio->bio.bi_status);
@@ -351,7 +351,7 @@ static void btrfs_simple_end_io(struct bio *bio)
 	if (bio->bi_status)
 		btrfs_log_dev_io_error(bio, dev);
 
-	if (bio_op(bio) == REQ_OP_READ) {
+	if (bio_op(bio) == REQ_OP_READ || bbio->uncached_io) {
 		INIT_WORK(&bbio->end_io_work, btrfs_end_bio_work);
 		queue_work(btrfs_end_io_wq(fs_info, bio), &bbio->end_io_work);
 	} else {
diff --git a/fs/btrfs/bio.h b/fs/btrfs/bio.h
index e2fe16074ad6..39b98326c98f 100644
--- a/fs/btrfs/bio.h
+++ b/fs/btrfs/bio.h
@@ -82,6 +82,8 @@ struct btrfs_bio {
 	/* Save the first error status of split bio. */
 	blk_status_t status;
 
+	bool uncached_io;
+
 	/*
 	 * This member must come last, bio_alloc_bioset will allocate enough
 	 * bytes for entire btrfs_bio but relies on bio being last.
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 872cca54cc6c..b97b21178ed7 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -760,8 +760,11 @@ static void submit_extent_folio(struct btrfs_bio_ctrl *bio_ctrl,
 	ASSERT(bio_ctrl->end_io_func);
 
 	if (bio_ctrl->bbio &&
-	    !btrfs_bio_is_contig(bio_ctrl, folio, disk_bytenr, pg_offset))
+	    !btrfs_bio_is_contig(bio_ctrl, folio, disk_bytenr, pg_offset)) {
+		if (folio_test_uncached(folio))
+			bio_ctrl->bbio->uncached_io = true;
 		submit_one_bio(bio_ctrl);
+	}
 
 	do {
 		u32 len = size;
@@ -779,6 +782,9 @@ static void submit_extent_folio(struct btrfs_bio_ctrl *bio_ctrl,
 			len = bio_ctrl->len_to_oe_boundary;
 		}
 
+		if (folio_test_uncached(folio))
+			bio_ctrl->bbio->uncached_io = true;
+
 		if (!bio_add_folio(&bio_ctrl->bbio->bio, folio, len, pg_offset)) {
 			/* bio full: move on to a new one */
 			submit_one_bio(bio_ctrl);
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 4fb521d91b06..cfee783f4c4d 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -919,7 +919,7 @@ static gfp_t get_prepare_gfp_flags(struct inode *inode, bool nowait)
 static noinline int prepare_pages(struct inode *inode, struct page **pages,
 				  size_t num_pages, loff_t pos,
 				  size_t write_bytes, bool force_uptodate,
-				  bool nowait)
+				  bool nowait, bool uncached)
 {
 	int i;
 	unsigned long index = pos >> PAGE_SHIFT;
@@ -928,6 +928,8 @@ static noinline int prepare_pages(struct inode *inode, struct page **pages,
 	int ret = 0;
 	int faili;
 
+	if (uncached)
+		fgp_flags |= FGP_UNCACHED;
 	for (i = 0; i < num_pages; i++) {
 again:
 		pages[i] = pagecache_get_page(inode->i_mapping, index + i,
@@ -1323,7 +1325,8 @@ ssize_t btrfs_buffered_write(struct kiocb *iocb, struct iov_iter *i)
 		 * contents of pages from loop to loop
 		 */
 		ret = prepare_pages(inode, pages, num_pages,
-				    pos, write_bytes, force_page_uptodate, false);
+				    pos, write_bytes, force_page_uptodate,
+				    false, iocb->ki_flags & IOCB_UNCACHED);
 		if (ret) {
 			btrfs_delalloc_release_extents(BTRFS_I(inode),
 						       reserve_bytes);
@@ -3802,7 +3805,7 @@ const struct file_operations btrfs_file_operations = {
 	.compat_ioctl	= btrfs_compat_ioctl,
 #endif
 	.remap_file_range = btrfs_remap_file_range,
-	.fop_flags	= FOP_BUFFER_RASYNC | FOP_BUFFER_WASYNC,
+	.fop_flags	= FOP_BUFFER_RASYNC | FOP_BUFFER_WASYNC | FOP_UNCACHED,
 };
 
 int btrfs_fdatawrite_range(struct btrfs_inode *inode, loff_t start, loff_t end)
-- 
2.45.2