FAILED: patch "[PATCH] direct-io: Fix negative return from dio read beyond eof" failed to apply to 3.14-stable tree

The patch below does not apply to the 3.14-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: Jan Kara <[email protected]>
Date: Mon, 30 Nov 2015 10:15:42 -0700
Subject: [PATCH] direct-io: Fix negative return from dio read beyond eof

Assume a filesystem with 4KB blocks. When a file has size 1000 bytes and we issue direct IO read at offset 1024, blockdev_direct_IO() reads the tail of the last block and the logic for handling short DIO reads in dio_complete() results in a return value -24 (1000 - 1024) which obviously confuses userspace.

Fix the problem by bailing out early once we sample i_size and can reliably check that direct IO read starts beyond i_size.

index cb5337d8c273..1c75a3a07f8f 100644
@@ -1169,6 +1169,15 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
 		}
 	}
 
+	/* Once we sampled i_size check for reads beyond EOF */
+	dio->i_size = i_size_read(inode);
+	if (iov_iter_rw(iter) == READ && offset >= dio->i_size) {
+		if (dio->flags & DIO_LOCKING)
+			mutex_unlock(&inode->i_mutex);
+		kmem_cache_free(dio_cache, dio);
+		goto out;
+	}
+
 	/*
 	 * For file extending writes updating i_size before data writeouts
 	 * complete can expose uninitialized blocks in dumb filesystems.

@@ -1222,7 +1231,6 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
 	sdio.next_block_for_io = -1;
 
 	dio->iocb = iocb;
-	dio->i_size = i_size_read(inode);
 
 	spin_lock_init(&dio->bio_lock);
 	dio->refcount = 1;