[PATCH 05/11] block: add polled wakeup task helper

[Jens Axboe <axboe@xxxxxxxxx>]

If we're polling for IO on a device that doesn't use interrupts, then
IO completion loop (and wake of task) is done by submitting task itself.
If that is the case, then we don't need to enter the wake_up_process()
function, we can simply mark ourselves as TASK_RUNNING.

Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
 fs/block_dev.c         |  4 ++--
 fs/iomap.c             |  2 +-
 include/linux/blkdev.h | 13 +++++++++++++
 mm/page_io.c           |  2 +-
 4 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 5b754f84c814..0ed9be8906a8 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -181,7 +181,7 @@ static void blkdev_bio_end_io_simple(struct bio *bio)
 	struct task_struct *waiter = bio->bi_private;
 
 	WRITE_ONCE(bio->bi_private, NULL);
-	wake_up_process(waiter);
+	blk_wake_io_task(waiter);
 }
 
 static ssize_t
@@ -308,7 +308,7 @@ static void blkdev_bio_end_io(struct bio *bio)
 			struct task_struct *waiter = dio->waiter;
 
 			WRITE_ONCE(dio->waiter, NULL);
-			wake_up_process(waiter);
+			blk_wake_io_task(waiter);
 		}
 	}
 
diff --git a/fs/iomap.c b/fs/iomap.c
index 3373ea4984d9..38c9bc63296a 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -1525,7 +1525,7 @@ static void iomap_dio_bio_end_io(struct bio *bio)
 		if (dio->wait_for_completion) {
 			struct task_struct *waiter = dio->submit.waiter;
 			WRITE_ONCE(dio->submit.waiter, NULL);
-			wake_up_process(waiter);
+			blk_wake_io_task(waiter);
 		} else if (dio->flags & IOMAP_DIO_WRITE) {
 			struct inode *inode = file_inode(dio->iocb->ki_filp);
 
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 41aaa05e42c1..91c44f7a7f62 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1772,4 +1772,17 @@ static inline int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
 
 #endif /* CONFIG_BLOCK */
 
+static inline void blk_wake_io_task(struct task_struct *waiter)
+{
+	/*
+	 * If we're polling, the task itself is doing the completions. For
+	 * that case, we don't need to signal a wakeup, it's enough to just
+	 * mark us as RUNNING.
+	 */
+	if (waiter == current)
+		__set_current_state(TASK_RUNNING);
+	else
+		wake_up_process(waiter);
+}
+
 #endif
diff --git a/mm/page_io.c b/mm/page_io.c
index 008f6d00c47c..f277459db805 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -140,7 +140,7 @@ static void end_swap_bio_read(struct bio *bio)
 	unlock_page(page);
 	WRITE_ONCE(bio->bi_private, NULL);
 	bio_put(bio);
-	wake_up_process(waiter);
+	blk_wake_io_task(waiter);
 	put_task_struct(waiter);
 }
 
-- 
2.17.1