linux-kernel - [PATCH 2/2] io_uring: only wake when the correct events are set

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Message-ID: <20220512091834.728610-3-dylany@fb.com>
Date:   Thu, 12 May 2022 02:18:34 -0700
From:   Dylan Yudaken <dylany@...com>
To:     Jens Axboe <axboe@...nel.dk>,
        Pavel Begunkov <asml.silence@...il.com>
CC:     <io-uring@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <kernel-team@...com>, Dylan Yudaken <dylany@...com>
Subject: [PATCH 2/2] io_uring: only wake when the correct events are set

The check for waking up a request compares the poll_t bits, however this
will always contain some common flags so this always wakes up.

For files with single wait queues such as sockets this can cause the
request to be sent to the async worker unnecesarily. Further if it is
non-blocking will complete the request with EAGAIN which is not desired.

Here exclude these common events, making sure to not exclude POLLERR which
might be important.

Fixes: d7718a9d25a6 ("io_uring: use poll driven retry for files that support it")
Signed-off-by: Dylan Yudaken <dylany@...com>
---
 fs/io_uring.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 44c57dca358d..44661a1f695a 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -6782,6 +6782,7 @@ static void io_poll_cancel_req(struct io_kiocb *req)
 
 #define wqe_to_req(wait)	((void *)((unsigned long) (wait)->private & ~1))
 #define wqe_is_double(wait)	((unsigned long) (wait)->private & 1)
+#define IO_ASYNC_POLL_COMMON	(EPOLLONESHOT | POLLPRI)
 
 static int io_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
 			void *key)
@@ -6816,7 +6817,7 @@ static int io_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
 	}
 
 	/* for instances that support it check for an event match first */
-	if (mask && !(mask & poll->events))
+	if (mask && !(mask & (poll->events & ~IO_ASYNC_POLL_COMMON)))
 		return 0;
 
 	if (io_poll_get_ownership(req)) {
@@ -6973,7 +6974,7 @@ static int io_arm_poll_handler(struct io_kiocb *req, unsigned issue_flags)
 	struct io_ring_ctx *ctx = req->ctx;
 	struct async_poll *apoll;
 	struct io_poll_table ipt;
-	__poll_t mask = EPOLLONESHOT | POLLERR | POLLPRI;
+	__poll_t mask = IO_ASYNC_POLL_COMMON | POLLERR;
 	int ret;
 
 	if (!def->pollin && !def->pollout)
-- 
2.30.2