FAILED: patch "[PATCH] ext4: fix data corruption caused by overlapping unaligned and" failed to apply to 4.4-stable tree

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 57a0da28ced8707cb9f79f071a016b9d005caf5a Mon Sep 17 00:00:00 2001
From: Lukas Czerner <[email protected]>
Date: Fri, 10 May 2019 21:45:33 -0400
Subject: [PATCH] ext4: fix data corruption caused by overlapping unaligned and
aligned IO

Unaligned AIO must be serialized because the zeroing of partial blocks of unaligned AIO can result in data corruption in case it's overlapping another in flight IO.

Currently we wait for all unwritten extents before we submit unaligned AIO which protects data in case of unaligned AIO is following overlapping IO. However if a unaligned AIO is followed by overlapping aligned AIO we can still end up corrupting data.

To fix this, we must make sure that the unaligned AIO is the only IO in flight by waiting for unwritten extents conversion not just before the IO submission, but right after it as well.

This problem can be reproduced by xfstest generic/538

index 98ec11f69cd4..2c5baa5e8291 100644
@@ -264,6 +264,13 @@ ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	}
 
 	ret = __generic_file_write_iter(iocb, from);
+	/*
+	 * Unaligned direct AIO must be the only IO in flight. Otherwise
+	 * overlapping aligned IO after unaligned might result in data
+	 * corruption.
+	 */
+	if (ret == -EIOCBQUEUED && unaligned_aio)
+		ext4_unwritten_wait(inode);
 	inode_unlock(inode);
 
 	if (ret > 0)