diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index f853835c409c..f3ff57b93158 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -268,6 +268,21 @@ static inline void btrfs_mod_outstanding_extents(struct btrfs_inode *inode,
 						  mod);
 }
 
+/*
+ * Called every time after doing a buffered, direct IO or memory mapped write.
+ *
+ * This is to ensure that if we write to a file that was previously fsynced in
+ * the current transaction, then try to fsync it again in the same transaction,
+ * we will know that there were changes in the file and that it needs to be
+ * logged.
+ */
+static inline void btrfs_set_inode_last_sub_trans(struct btrfs_inode *inode)
+{
+	spin_lock(&inode->lock);
+	inode->last_sub_trans = inode->root->log_transid;
+	spin_unlock(&inode->lock);
+}
+
 static inline int btrfs_inode_in_log(struct btrfs_inode *inode, u64 generation)
 {
 	int ret = 0;
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 400b0717b9d4..1279359ed172 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2004,14 +2004,8 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
 
 	inode_unlock(inode);
 
-	/*
-	 * We also have to set last_sub_trans to the current log transid,
-	 * otherwise subsequent syncs to a file that's been synced in this
-	 * transaction will appear to have already occurred.
-	 */
-	spin_lock(&BTRFS_I(inode)->lock);
-	BTRFS_I(inode)->last_sub_trans = root->log_transid;
-	spin_unlock(&BTRFS_I(inode)->lock);
+	btrfs_set_inode_last_sub_trans(BTRFS_I(inode));
+
 	if (num_written > 0)
 		num_written = generic_write_sync(iocb, num_written);
 
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 54b607a3cc3f..29552d4f6845 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -9250,9 +9250,7 @@ again:
 	set_page_dirty(page);
 	SetPageUptodate(page);
 
-	BTRFS_I(inode)->last_trans = fs_info->generation;
-	BTRFS_I(inode)->last_sub_trans = BTRFS_I(inode)->root->log_transid;
-	BTRFS_I(inode)->last_log_commit = BTRFS_I(inode)->root->last_log_commit;
+	btrfs_set_inode_last_sub_trans(BTRFS_I(inode));
 
 	unlock_extent_cached(io_tree, page_start, page_end, &cached_state);
 
diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index d8a7d460e436..cbede328bda5 100644
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -160,7 +160,7 @@ static inline void btrfs_set_inode_last_trans(struct btrfs_trans_handle *trans,
 	spin_lock(&BTRFS_I(inode)->lock);
 	BTRFS_I(inode)->last_trans = trans->transaction->transid;
 	BTRFS_I(inode)->last_sub_trans = BTRFS_I(inode)->root->log_transid;
-	BTRFS_I(inode)->last_log_commit = BTRFS_I(inode)->root->last_log_commit;
+	BTRFS_I(inode)->last_log_commit = BTRFS_I(inode)->last_sub_trans - 1;
 	spin_unlock(&BTRFS_I(inode)->lock);
 }