block_dev: only write bdev inode on close

Since 018a17bdc865 ("bdi: reimplement bdev_inode_switch_bdi()") the
block device code writes out all dirty data whenever switching the
backing_dev_info for a block device inode.  But a block device inode can
only be dirtied when it is in use, which means we only have to write it
out on the final blkdev_put, but not when doing a blkdev_get.

Factoring out the write out from the bdi list switch prepares from
removing the list switch later in the series.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 19 insertions, 12 deletions

diff --git a/fs/block_dev.c b/fs/block_dev.c
index b48c41bf0f86..026ca7b8431c 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -49,6 +49,17 @@ inline struct block_device *I_BDEV(struct inode *inode)
 }
 EXPORT_SYMBOL(I_BDEV);
 
+static void bdev_write_inode(struct inode *inode)
+{
+        spin_lock(&inode->i_lock);
+        while (inode->i_state & I_DIRTY) {
+                spin_unlock(&inode->i_lock);
+                WARN_ON_ONCE(write_inode_now(inode, true));
+                spin_lock(&inode->i_lock);
+        }
+        spin_unlock(&inode->i_lock);
+}
+
 /*
  * Move the inode from its current bdi to a new bdi.  Make sure the inode
  * is clean before moving so that it doesn't linger on the old bdi.
@@ -56,16 +67,10 @@ EXPORT_SYMBOL(I_BDEV);
 static void bdev_inode_switch_bdi(struct inode *inode,
                         struct backing_dev_info *dst)
 {
-        while (true) {
-                spin_lock(&inode->i_lock);
-                if (!(inode->i_state & I_DIRTY)) {
-                        inode->i_data.backing_dev_info = dst;
-                        spin_unlock(&inode->i_lock);
-                        return;
-                }
-                spin_unlock(&inode->i_lock);
-                WARN_ON_ONCE(write_inode_now(inode, true));
-        }
+        spin_lock(&inode->i_lock);
+        WARN_ON_ONCE(inode->i_state & I_DIRTY);
+        inode->i_data.backing_dev_info = dst;
+        spin_unlock(&inode->i_lock);
 }
 
 /* Kill _all_ buffers and pagecache , dirty or not.. */
@@ -1464,9 +1469,11 @@ static void __blkdev_put(struct block_device *bdev, fmode_t mode, int for_part)
                 WARN_ON_ONCE(bdev->bd_holders);
                 sync_blockdev(bdev);
                 kill_bdev(bdev);
-                /* ->release can cause the old bdi to disappear,
-                 * so must switch it out first
+                /*
+                 * ->release can cause the queue to disappear, so flush all
+                 * dirty data before.
                  */
+                bdev_write_inode(bdev->bd_inode);
                 bdev_inode_switch_bdi(bdev->bd_inode,
                                         &default_backing_dev_info);
         }