[PATCH v3 RESEND] iomap: set REQ_NOWAIT according to IOCB_NOWAIT in Direct IO

[Hao Xu <haoxu@linux.alibaba.com>]

Currently, IOCB_NOWAIT is ignored in Direct IO, REQ_NOWAIT is only set
when IOCB_HIPRI is set. But REQ_NOWAIT should be set as well when
IOCB_NOWAIT is set.

Suggested-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
---

Hi all,
I tested fio io_uring direct read for a file on ext4 filesystem on a
nvme ssd. I found that IOCB_NOWAIT is ignored in iomap layer, which
means REQ_NOWAIT is not set in bio->bi_opf. This makes nowait IO a
normal IO. Since I'm new to iomap and block layer, I sincerely ask
yours opinions in case I misunderstand the code which is very likely
to happen.:)
The example I use: io_uring direct randread, the first try is with
IOCB_NOWAIT but not IOCB_HIPRI, the IOCB_NOWAIT is ignored in block
layer which I think is not the designed behaviour.

I found that Konstantin found this issue before in May
2020 (https://www.spinics.net/lists/linux-block/msg53275.html), here add
his signature, add Jeffle's as well since he gave me some help.

v1->v2:
* add same logic in __blkdev_direct_IO_simple()
v2->v3:
* add same logic in do_blockdev_direct_IO()

 fs/block_dev.c       | 7 +++++++
 fs/direct-io.c       | 6 ++++--
 fs/iomap/direct-io.c | 3 +++
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 9e84b1928b94..ca6f365c2f14 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -263,6 +263,10 @@ static void blkdev_bio_end_io_simple(struct bio *bio)
 		bio.bi_opf = dio_bio_write_op(iocb);
 		task_io_account_write(ret);
 	}
+
+	if (iocb->ki_flags & IOCB_NOWAIT)
+		bio.bi_opf |= REQ_NOWAIT;
+
 	if (iocb->ki_flags & IOCB_HIPRI)
 		bio_set_polled(&bio, iocb);
 
@@ -417,6 +421,9 @@ static void blkdev_bio_end_io(struct bio *bio)
 			task_io_account_write(bio->bi_iter.bi_size);
 		}
 
+		if (iocb->ki_flags & IOCB_NOWAIT)
+			bio->bi_opf |= REQ_NOWAIT;
+
 		dio->size += bio->bi_iter.bi_size;
 		pos += bio->bi_iter.bi_size;
 
diff --git a/fs/direct-io.c b/fs/direct-io.c
index d53fa92a1ab6..b221ed351c1c 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -1206,11 +1206,13 @@ static inline int drop_refcount(struct dio *dio)
 	if (iov_iter_rw(iter) == WRITE) {
 		dio->op = REQ_OP_WRITE;
 		dio->op_flags = REQ_SYNC | REQ_IDLE;
-		if (iocb->ki_flags & IOCB_NOWAIT)
-			dio->op_flags |= REQ_NOWAIT;
 	} else {
 		dio->op = REQ_OP_READ;
 	}
+
+	if (iocb->ki_flags & IOCB_NOWAIT)
+		dio->op_flags |= REQ_NOWAIT;
+
 	if (iocb->ki_flags & IOCB_HIPRI)
 		dio->op_flags |= REQ_HIPRI;
 
diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 933f234d5bec..2e897688ed6d 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -64,6 +64,9 @@ static void iomap_dio_submit_bio(struct iomap_dio *dio, struct iomap *iomap,
 {
 	atomic_inc(&dio->ref);
 
+	if (dio->iocb->ki_flags & IOCB_NOWAIT)
+		bio->bi_opf |= REQ_NOWAIT;
+
 	if (dio->iocb->ki_flags & IOCB_HIPRI)
 		bio_set_polled(bio, dio->iocb);
 
-- 
1.8.3.1