From: Jens Axboe <axboe@kernel.dk>
Date: Wed, 14 Nov 2018 04:16:54 +0000 (-0700)
Subject: block: add polled wakeup task helper
X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=0619317ff8baa2da9238191ad5167ed3618c16d9;p=openwrt%2Fstaging%2Fblogic.git

block: add polled wakeup task helper

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.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---

diff --git a/fs/block_dev.c b/fs/block_dev.c
index c039abfb2052..9fe56672cfe5 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
@@ -305,7 +305,7 @@ 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 f61d13dfdf09..b0462b363bad 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 d4d1c89bcddd..57572ff46016 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -140,7 +140,7 @@ out:
 	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);
 }