[PATCH RFC v2 06/13] ext4: sync inode metadata in ext4_evict_inode()

[Christian Brauner <brauner@kernel.org>]

Without a journal ext4_mark_iloc_dirty() copies the inode into the inode
table block, marks the block dirty and sets I_METADATA_WRITEBACK so that
a later fsync() writes the block out and waits for it. But the bit goes
away with the inode. If the inode is evicted and read back in, fsync()
finds a clean inode and returns while the block might still be dirty or
under writeback.

Right now that can't happen because inode_lru_isolate() never lets go
of an inode with I_METADATA_WRITEBACK set. That is about to change.

So call ext4_sync_inode_metadata() from ext4_evict_inode() for a linked
inode that still has the bit set. It syncs the metadata buffers as well
so it replaces the mmb_sync() there, and since the previous patch it
doesn't read anything from disk. With a journal the bit is never set
and nothing changes.

Suggested-by: Jan Kara <jack@suse.cz>
Cc: stable@vger.kernel.org # v7.3
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 fs/ext4/inode.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 18362580097f..c64cedd86826 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -261,9 +261,19 @@ void ext4_evict_inode(struct inode *inode)
 			ext4_warning_inode(inode, "data will be lost");
 
 		truncate_inode_pages_final(&inode->i_data);
-		mmb = ext4_i_metadata_bhs(inode);
-		if (mmb)
-			mmb_sync(mmb);
+		/*
+		 * fsync() can't find what I_METADATA_WRITEBACK tracks once the
+		 * inode is gone. This syncs the metadata buffers as well.
+		 */
+		if (inode_state_read_once(inode) & I_METADATA_WRITEBACK) {
+			ext4_sync_inode_metadata(inode, &(struct writeback_control) {
+				.sync_mode = WB_SYNC_ALL,
+			});
+		} else {
+			mmb = ext4_i_metadata_bhs(inode);
+			if (mmb)
+				mmb_sync(mmb);
+		}
 		goto no_delete;
 	}
 

-- 
2.53.0