[PATCH 1/2] block: Add post_release() operation

[Bart Van Assche <bvanassche@acm.org>]

Add post_release() block device operation which provides a hook for
performing synchronous cleanup without disk->open_mutex held.
This is needed by block drivers (such as the loop device) that must
drain in-flight I/O and perform synchronization after disk->open_mutex
has been released.

Suggested-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 block/bdev.c                     | 3 +++
 include/linux/blkdev.h           | 5 +++++
 rust/kernel/block/mq/gen_disk.rs | 1 +
 3 files changed, 9 insertions(+)

diff --git a/block/bdev.c b/block/bdev.c
index fac74319e9fb..350f3c29d682 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -1189,6 +1189,9 @@ void bdev_release(struct file *bdev_file)
 		blkdev_put_whole(bdev);
 	mutex_unlock(&disk->open_mutex);
 
+	if (disk->fops->post_release)
+		disk->fops->post_release(disk);
+
 	module_put(disk->fops->owner);
 put_no_open:
 	blkdev_put_no_open(bdev);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index d003a9d2d1f6..b35f8af1243e 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1580,6 +1580,11 @@ struct block_device_operations {
 			unsigned int flags);
 	int (*open)(struct gendisk *disk, blk_mode_t mode);
 	void (*release)(struct gendisk *disk);
+	/*
+	 * Called after disk->open_mutex is released in the bdev_release() path,
+	 * after .release(). Implementations may sleep.
+	 */
+	void (*post_release)(struct gendisk *disk);
 	int (*ioctl)(struct block_device *bdev, blk_mode_t mode,
 			unsigned cmd, unsigned long arg);
 	int (*compat_ioctl)(struct block_device *bdev, blk_mode_t mode,
diff --git a/rust/kernel/block/mq/gen_disk.rs b/rust/kernel/block/mq/gen_disk.rs
index fc97dd873974..2ff77ef49781 100644
--- a/rust/kernel/block/mq/gen_disk.rs
+++ b/rust/kernel/block/mq/gen_disk.rs
@@ -129,6 +129,7 @@ pub fn build<T: Operations>(
             submit_bio: None,
             open: None,
             release: None,
+            post_release: None,
             ioctl: None,
             compat_ioctl: None,
             check_events: None,