From: Christoph Hellwig <hch@lst.de>
Date: Tue, 12 Oct 2021 13:12:20 +0200
Subject: [PATCH] io_uring: don't sleep when polling for I/O
Git-commit: d729cf9acb9311956c8a37113dcfa0160a2d9665
Patch-mainline: v5.16-rc1
References: jsc#PED-1183

There is no point in sleeping for the expected I/O completion timeout
in the io_uring async polling model as we never poll for a specific
I/O.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Mark Wunderlich <mark.wunderlich@intel.com>
Link: https://lore.kernel.org/r/20211012111226.760968-11-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Hannes Reinecke <hare@suse.com>
---
 block/blk-mq.c         | 3 ++-
 fs/io_uring.c          | 2 +-
 include/linux/blkdev.h | 2 ++
 3 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 6609e10657a8..97c24e461d0a 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -4103,7 +4103,8 @@ int blk_poll(struct request_queue *q, blk_qc_t cookie, unsigned int flags)
 	if (current->plug)
 		blk_flush_plug_list(current->plug, false);
 
-	if (q->poll_nsec != BLK_MQ_POLL_CLASSIC) {
+	if (!(flags & BLK_POLL_NOSLEEP) &&
+	    q->poll_nsec != BLK_MQ_POLL_CLASSIC) {
 		if (blk_mq_poll_hybrid(q, cookie))
 			return 1;
 	}
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 541fec2bd49a..c5066146b8de 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2457,7 +2457,7 @@ static int io_do_iopoll(struct io_ring_ctx *ctx, unsigned int *nr_events,
 			long min)
 {
 	struct io_kiocb *req, *tmp;
-	unsigned int poll_flags = 0;
+	unsigned int poll_flags = BLK_POLL_NOSLEEP;
 	LIST_HEAD(done);
 
 	/*
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index e177346bc020..2b80c98fc373 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -566,6 +566,8 @@ blk_status_t errno_to_blk_status(int errno);
 
 /* only poll the hardware once, don't continue until a completion was found */
 #define BLK_POLL_ONESHOT		(1 << 0)
+/* do not sleep to wait for the expected completion time */
+#define BLK_POLL_NOSLEEP		(1 << 1)
 int blk_poll(struct request_queue *q, blk_qc_t cookie, unsigned int flags);
 
 static inline struct request_queue *bdev_get_queue(struct block_device *bdev)
-- 
2.35.3