linux-kernel - [PATCH v1] fs/io_uring: Hoist ret2 == -EAGAIN check in tail of io

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Date:   Mon, 18 Oct 2021 03:02:43 -0400
From:   Noah Goldstein <goldstein.w.n@...il.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     goldstein.w.n@...il.com, axboe@...nel.dk, asml.silence@...il.com,
        io-uring@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v1] fs/io_uring: Hoist ret2 == -EAGAIN check in tail of io_write

This commit reorganizes the branches in the tail of io_write so that
the 'ret2 == -EAGAIN' check is not repeated and done first.

The previous version was duplicating the 'ret2 == -EAGAIN'. As well
'ret2 != -EAGAIN' gurantees the 'done:' path so it makes sense to
move that check to the front before the likely more expensive branches
which require memory derefences.

Signed-off-by: Noah Goldstein <goldstein.w.n@...il.com>
---
Generally I would want to rewrite this as:
```
if (ret2 != -EAGAIN
    || (req->flags & REQ_F_NOWAIT)
    || (!force_nonblock && !(req->ctx->flags & IORING_SETUP_IOPOLL)))
        kiocb_done(kiocb, ret2, issue_flags);
else {
    ...
```

But the style of the file seems to be to use gotos. If the above is
prefereable, let me know and I'll post a new version.    
 fs/io_uring.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index d1e672e7a2d1..932fc84d70d3 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3648,12 +3648,15 @@ static int io_write(struct io_kiocb *req, unsigned int issue_flags)
 	 */
 	if (ret2 == -EOPNOTSUPP && (kiocb->ki_flags & IOCB_NOWAIT))
 		ret2 = -EAGAIN;
+
+	if (ret2 != -EAGAIN)
+		goto done;
 	/* no retry on NONBLOCK nor RWF_NOWAIT */
-	if (ret2 == -EAGAIN && (req->flags & REQ_F_NOWAIT))
+	if (req->flags & REQ_F_NOWAIT)
 		goto done;
-	if (!force_nonblock || ret2 != -EAGAIN) {
+	if (!force_nonblock) {
 		/* IOPOLL retry should happen for io-wq threads */
-		if (ret2 == -EAGAIN && (req->ctx->flags & IORING_SETUP_IOPOLL))
+		if (req->ctx->flags & IORING_SETUP_IOPOLL)
 			goto copy_iov;
 done:
 		kiocb_done(kiocb, ret2, issue_flags);
-- 
2.29.2