linux-kernel - [PATCH 1/2] io_uring: fix hanging iopoll in case of -EAGAIN

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Message-Id: <22111b29e298f5f606130fcf4307bda99dbec089.1593077359.git.asml.silence@gmail.com>
Date:   Thu, 25 Jun 2020 12:37:10 +0300
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Jens Axboe <axboe@...nel.dk>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] io_uring: fix hanging iopoll in case of -EAGAIN

io_do_iopoll() won't do anything with a request unless
req->iopoll_completed is set. So io_complete_rw_iopoll() has to set
it, otherwise io_do_iopoll() will poll a file again and again even
though the request of interest was completed long time ago.

Also, remove -EAGAIN check from io_issue_sqe() as it races with
the changed lines. The request will take the long way and be
resubmitted from io_iopoll*().

Fixes: bbde017a32b3 ("io_uring: add memory barrier to synchronize
io_kiocb's result and iopoll_completed")
Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
---
 fs/io_uring.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index c686061c3762..fb88a537f471 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2104,10 +2104,8 @@ static void io_complete_rw_iopoll(struct kiocb *kiocb, long res, long res2)
 
 	WRITE_ONCE(req->result, res);
 	/* order with io_poll_complete() checking ->result */
-	if (res != -EAGAIN) {
-		smp_wmb();
-		WRITE_ONCE(req->iopoll_completed, 1);
-	}
+	smp_wmb();
+	WRITE_ONCE(req->iopoll_completed, 1);
 }
 
 /*
@@ -5592,9 +5590,6 @@ static int io_issue_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	if ((ctx->flags & IORING_SETUP_IOPOLL) && req->file) {
 		const bool in_async = io_wq_current_is_worker();
 
-		if (req->result == -EAGAIN)
-			return -EAGAIN;
-
 		/* workqueue context doesn't hold uring_lock, grab it now */
 		if (in_async)
 			mutex_lock(&ctx->uring_lock);
-- 
2.24.0