[PATCHSET 0/2] io_uring tweaks for poll retry

[PATCHSET 0/2] io_uring tweaks for poll retry

[Jens Axboe]

Just a few minor tweaks here:

- Base decision on whether we can support async EAGAIN try on a file on
  whether it has ->read_iter or ->write_iter, depending on direction.

- Only force punt to async worker for read/write if we can't poll for
  the retry.

Should go into 5.7.

-- 
Jens Axboe

[PATCH 1/2] io_uring: enable poll retry for any file with ->read_iter / ->write_iter

[Jens Axboe]

We can have files like eventfd where it's perfectly fine to do poll
based retry on them, right now io_file_supports_async() doesn't take
that into account.

Pass in data direction and check the f_op instead of just always needing
an async worker.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 084dfade5cda..53cadadc7f89 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2038,7 +2038,7 @@ static struct file *__io_file_get(struct io_submit_state *state, int fd)
  * any file. For now, just ensure that anything potentially problematic is done
  * inline.
  */
-static bool io_file_supports_async(struct file *file)
+static bool io_file_supports_async(struct file *file, int rw)
 {
 	umode_t mode = file_inode(file)->i_mode;
 
@@ -2047,7 +2047,10 @@ static bool io_file_supports_async(struct file *file)
 	if (S_ISREG(mode) && file->f_op != &io_uring_fops)
 		return true;
 
-	return false;
+	if (rw == READ)
+		return file->f_op->read_iter != NULL;
+
+	return file->f_op->write_iter != NULL;
 }
 
 static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
@@ -2575,7 +2578,7 @@ static int io_read(struct io_kiocb *req, bool force_nonblock)
 	 * If the file doesn't support async, mark it as REQ_F_MUST_PUNT so
 	 * we know to async punt it even if it was opened O_NONBLOCK
 	 */
-	if (force_nonblock && !io_file_supports_async(req->file))
+	if (force_nonblock && !io_file_supports_async(req->file, READ))
 		goto copy_iov;
 
 	iov_count = iov_iter_count(&iter);
@@ -2666,7 +2669,7 @@ static int io_write(struct io_kiocb *req, bool force_nonblock)
 	 * If the file doesn't support async, mark it as REQ_F_MUST_PUNT so
 	 * we know to async punt it even if it was opened O_NONBLOCK
 	 */
-	if (force_nonblock && !io_file_supports_async(req->file))
+	if (force_nonblock && !io_file_supports_async(req->file, WRITE))
 		goto copy_iov;
 
 	/* file path doesn't support NOWAIT for non-direct_IO */
@@ -2760,11 +2763,11 @@ static int io_splice_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	return 0;
 }
 
-static bool io_splice_punt(struct file *file)
+static bool io_splice_punt(struct file *file, int rw)
 {
 	if (get_pipe_info(file))
 		return false;
-	if (!io_file_supports_async(file))
+	if (!io_file_supports_async(file, rw))
 		return true;
 	return !(file->f_flags & O_NONBLOCK);
 }
@@ -2779,7 +2782,7 @@ static int io_splice(struct io_kiocb *req, bool force_nonblock)
 	long ret;
 
 	if (force_nonblock) {
-		if (io_splice_punt(in) || io_splice_punt(out))
+		if (io_splice_punt(in, READ) || io_splice_punt(out, WRITE))
 			return -EAGAIN;
 		flags |= SPLICE_F_NONBLOCK;
 	}
-- 
2.26.2

[PATCH 2/2] io_uring: only force async punt if poll based retry can't handle it

[Jens Axboe]

We do blocking retry from our poll handler, if the file supports polled
notifications. Only mark the request as needing an async worker if we
can't poll for it.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 53cadadc7f89..75ff4cc9818b 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2601,7 +2601,8 @@ static int io_read(struct io_kiocb *req, bool force_nonblock)
 			if (ret)
 				goto out_free;
 			/* any defer here is final, must blocking retry */
-			if (!(req->flags & REQ_F_NOWAIT))
+			if (!(req->flags & REQ_F_NOWAIT) &&
+			    !file_can_poll(req->file))
 				req->flags |= REQ_F_MUST_PUNT;
 			return -EAGAIN;
 		}
@@ -2723,7 +2724,8 @@ static int io_write(struct io_kiocb *req, bool force_nonblock)
 			if (ret)
 				goto out_free;
 			/* any defer here is final, must blocking retry */
-			req->flags |= REQ_F_MUST_PUNT;
+			if (!file_can_poll(req->file))
+				req->flags |= REQ_F_MUST_PUNT;
 			return -EAGAIN;
 		}
 	}
-- 
2.26.2