block: call into the file system for ioctl BLKFLSBUF

BLKFLSBUF is a historic ioctl that is called on a file handle to a
block device and syncs either the file system mounted on that block
device if there is one, or otherwise the just the data on the block
device.

Replace the get_super based syncing with a holder operation to remove
the last usage of get_super, and to also support syncing the file system
if the block device is not the main block device stored in s_dev.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Message-Id: <20230811100828.1897174-16-hch@lst.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Christoph Hellwig

block/bdev.c

@@ -206,22 +206,6 @@ int sync_blockdev_range(struct block_device *bdev, loff_t lstart, loff_t lend)
 }
 EXPORT_SYMBOL(sync_blockdev_range);
 
-/*
- * Write out and wait upon all dirty data associated with this
- * device.   Filesystem data as well as the underlying block
- * device.  Takes the superblock lock.
- */
-int fsync_bdev(struct block_device *bdev)
-{
-	struct super_block *sb = get_super(bdev);
-	if (sb) {
-		int res = sync_filesystem(sb);
-		drop_super(sb);
-		return res;
-	}
-	return sync_blockdev(bdev);
-}
-
 /**
  * freeze_bdev - lock a filesystem and force it into a consistent state
  * @bdev:	blockdevice to lock

block/ioctl.c

@@ -364,7 +364,14 @@ static int blkdev_flushbuf(struct block_device *bdev, unsigned cmd,
 {
 	if (!capable(CAP_SYS_ADMIN))
 		return -EACCES;
-	fsync_bdev(bdev);
+
+	mutex_lock(&bdev->bd_holder_lock);
+	if (bdev->bd_holder_ops && bdev->bd_holder_ops->sync)
+		bdev->bd_holder_ops->sync(bdev);
+	else
+		sync_blockdev(bdev);
+	mutex_unlock(&bdev->bd_holder_lock);
+
 	invalidate_bdev(bdev);
 	return 0;
 }

fs/super.c

@@ -1248,8 +1248,21 @@ static void fs_bdev_mark_dead(struct block_device *bdev, bool surprise)
 	up_read(&sb->s_umount);
 }
 
+static void fs_bdev_sync(struct block_device *bdev)
+{
+	struct super_block *sb = bdev->bd_holder;
+
+	lockdep_assert_held(&bdev->bd_holder_lock);
+
+	if (!lock_active_super(sb))
+		return;
+	sync_filesystem(sb);
+	up_read(&sb->s_umount);
+}
+
 const struct blk_holder_ops fs_holder_ops = {
 	.mark_dead		= fs_bdev_mark_dead,
+	.sync			= fs_bdev_sync,
 };
 EXPORT_SYMBOL_GPL(fs_holder_ops);
 

include/linux/blkdev.h

@@ -1462,6 +1462,11 @@ void blkdev_show(struct seq_file *seqf, off_t offset);
 
 struct blk_holder_ops {
 	void (*mark_dead)(struct block_device *bdev, bool surprise);
+
+	/*
+	 * Sync the file system mounted on the block device.
+	 */
+	void (*sync)(struct block_device *bdev);
 };
 
 extern const struct blk_holder_ops fs_holder_ops;
@@ -1524,8 +1529,6 @@ static inline int early_lookup_bdev(const char *pathname, dev_t *dev)
 }
 #endif /* CONFIG_BLOCK */
 
-int fsync_bdev(struct block_device *bdev);
-
 int freeze_bdev(struct block_device *bdev);
 int thaw_bdev(struct block_device *bdev);