[PATCH RFC v3 08/14] fs: set I_METADATA_WRITEBACK in mmb_mark_buffer_dirty()

[Christian Brauner <brauner@kernel.org>]

ext2, ext4 without a journal, fat, udf and minix track the metadata
buffers of an inode in a mapping_metadata_bhs list and sync them from
->sync_inode_metadata() and ->evict_inode(). The inode block itself is
only tracked by I_METADATA_WRITEBACK which ->write_inode() sets after
copying the inode into its buffer.

Set the bit in mmb_mark_buffer_dirty() as well so that it covers all
the metadata an inode may still have to write out. Set it after the
buffer is on the list. An fsync() that sees the bit then also finds the
buffer when it walks the list, and one that cleared the bit before we
set it leaves it set for the next one.

The inode itself may never have been dirtied. fat for example tracks
the FAT buffers on a private inode that nothing marks dirty. So attach
the inode to a wb before setting the bit, the way ext4_mark_iloc_dirty()
does, or writeback_single_inode() has no wb to lock once evict() syncs
it.

That lets evict() write out everything the bit tracks in one place
instead of every ->evict_inode() calling mmb_sync() itself.

Suggested-by: Jan Kara <jack@suse.cz>
Cc: stable@vger.kernel.org # v7.3
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 fs/buffer.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 5d3852b726d6..f951559e7d32 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -621,12 +621,15 @@ void write_boundary_block(struct block_device *bdev,
  * @bh: The buffer to mark dirty.
  * @mmb: The list of buffers to add the buffer to.
  *
- * Mark the buffer dirty and add it to the list if it is not already on
- * a list.
+ * Mark the buffer dirty, add it to the list if it is not already on a list
+ * and set I_METADATA_WRITEBACK on the inode so that fsync() and eviction
+ * write it out.
  */
 void mmb_mark_buffer_dirty(struct buffer_head *bh,
 			   struct mapping_metadata_bhs *mmb)
 {
+	struct inode *inode = mmb->mapping->host;
+
 	mark_buffer_dirty(bh);
 	if (!bh->b_mmb) {
 		spin_lock(&mmb->lock);
@@ -641,6 +644,15 @@ void mmb_mark_buffer_dirty(struct buffer_head *bh,
 		list_move_tail(&bh->b_assoc_buffers, &mmb->list);
 		spin_unlock(&mmb->lock);
 	}
+	/*
+	 * The inode itself may never have been dirtied, so attach it to a wb
+	 * before setting the bit or writeback_single_inode() has nothing to
+	 * lock when evict() syncs it.
+	 */
+	spin_lock(&inode->i_lock);
+	inode_attach_wb(inode, NULL);
+	inode_state_set(inode, I_METADATA_WRITEBACK);
+	spin_unlock(&inode->i_lock);
 }
 EXPORT_SYMBOL(mmb_mark_buffer_dirty);
 

-- 
2.53.0