[PATCH 5.8 025/148] ext4: do not block RWF_NOWAIT dio write on unallocated space

[Greg Kroah-Hartman]

From: Jan Kara <jack@xxxxxxx>

commit 0b3171b6d195637f84ddf8b59bae818ea20bc8ac upstream.

Since commit 378f32bab371 ("ext4: introduce direct I/O write using iomap
infrastructure") we don't properly bail out of RWF_NOWAIT direct IO
write if underlying blocks are not allocated. Also
ext4_dio_write_checks() does not honor RWF_NOWAIT when re-acquiring
i_rwsem. Fix both issues.

Fixes: 378f32bab371 ("ext4: introduce direct I/O write using iomap infrastructure")
Cc: stable@xxxxxxxxxx
Reported-by: Filipe Manana <fdmanana@xxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
Reviewed-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20200708153516.9507-1-jack@xxxxxxx
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/ext4/file.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -428,6 +428,10 @@ restart:
 	 */
 	if (*ilock_shared && (!IS_NOSEC(inode) || *extend ||
 	     !ext4_overwrite_io(inode, offset, count))) {
+		if (iocb->ki_flags & IOCB_NOWAIT) {
+			ret = -EAGAIN;
+			goto out;
+		}
 		inode_unlock_shared(inode);
 		*ilock_shared = false;
 		inode_lock(inode);