linux-kernel - [PATCH 5.18 461/879] io_uring: only wake when the correct events are set

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Date:   Tue,  7 Jun 2022 18:59:39 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dylan Yudaken <dylany@...com>,
        Jens Axboe <axboe@...nel.dk>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.18 461/879] io_uring: only wake when the correct events are set

From: Dylan Yudaken <dylany@...com>

[ Upstream commit 1b1d7b4bf1d9948c8dba5ee550459ce7c65ac019 ]

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>
Link: https://lore.kernel.org/r/20220512091834.728610-3-dylany@fb.com
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 7272e410d24a..9e247335e70d 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5981,6 +5981,7 @@ 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)
@@ -6015,7 +6016,7 @@ 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)) {
@@ -6171,7 +6172,7 @@ 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)
-- 
2.35.1