[PATCH v7 4/5] buffer: set BIO_COMPLETE_IN_TASK for dropbehind writeback

Set BIO_COMPLETE_IN_TASK in __bh_submit() for write bios when the folio
has dropbehind set, so that buffer_head writeback completions get
deferred to task context where folio_end_dropbehind() can safely
invalidate folios.

Read completions are not deferred since dropbehind invalidation for
reads is handled synchronously by the reader.

Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Tal Zussman <[email protected]>
---
 fs/buffer.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/buffer.c b/fs/buffer.c
index 9af5f061a1f8..6f099847240e 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1203,6 +1203,9 @@ static void __bh_submit(struct buffer_head *bh, blk_opf_t opf,
 
 	bio = bio_alloc(bh->b_bdev, 1, opf, GFP_NOIO);
 
+	if (folio_test_dropbehind(bh->b_folio) && op_is_write(opf))
+		bio_set_flag(bio, BIO_COMPLETE_IN_TASK);
+
 	if (IS_ENABLED(CONFIG_FS_ENCRYPTION))
 		buffer_set_crypto_ctx(bio, bh, GFP_NOIO);
 

-- 
2.39.5