f2fs: fix inode rwsem regression

This is similar to 942491c9 ("xfs: fix AIM7 regression")
Apparently our current rwsem code doesn't like doing the trylock, then
lock for real scheme.  So change our read/write methods to just do the
trylock for the RWF_NOWAIT case.

We don't need a check for IOCB_NOWAIT and !direct-IO because it
is checked in generic_write_checks().

Fixes: b91050a8 ("f2fs: add nowait aio support")
Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/file.c

@@ -3230,11 +3230,12 @@ static ssize_t f2fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 		goto out;
 	}
 
-	if (!inode_trylock(inode)) {
 	if (iocb->ki_flags & IOCB_NOWAIT) {
+		if (!inode_trylock(inode)) {
 			ret = -EAGAIN;
 			goto out;
 		}
+	} else {
 		inode_lock(inode);
 	}