[PATCH v2 5/6] fs: Propagate write hints to the struct block_device inode

[Bart Van Assche <bvanassche@xxxxxxx>]

Write hints applied with F_SET_RW_HINT on a block device affect the
block device inode only. Propagate these hints to the inode associated
with struct block_device because that is the inode used when writing
back dirty pages.

Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Jeff Layton <jlayton@xxxxxxxxxx>
Cc: Chuck Lever <chuck.lever@xxxxxxxxxx>
Cc: Kanchan Joshi <joshi.k@xxxxxxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
 fs/fcntl.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/fcntl.c b/fs/fcntl.c
index 00be0a710bba..8eb6d64a985b 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -317,6 +317,13 @@ static long fcntl_set_rw_hint(struct file *file, unsigned int cmd,
 
 	WRITE_ONCE(inode->i_write_hint, hint);
 
+	/*
+	 * file->f_mapping->host may differ from inode. As an example,
+	 * blkdev_open() modifies file->f_mapping.
+	 */
+	if (file->f_mapping->host != inode)
+		WRITE_ONCE(file->f_mapping->host->i_write_hint, hint);
+
 	return 0;
 }