fuse: invalidate page cache pages before direct write

In FOPEN_DIRECT_IO, page cache may still be there for a file since private
mmap is allowed.  Direct write should respect that and invalidate the
corresponding pages so that page cache readers don't get stale data.
Signed-off-by: Hao Xu <howeyxu@tencent.com>
Tested-by: Jiachen Zhang <zhangjiachen.jaycee@bytedance.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/file.c

@@ -1428,7 +1428,8 @@ ssize_t fuse_direct_io(struct fuse_io_priv *io, struct iov_iter *iter,
 	int write = flags & FUSE_DIO_WRITE;
 	int cuse = flags & FUSE_DIO_CUSE;
 	struct file *file = io->iocb->ki_filp;
-	struct inode *inode = file->f_mapping->host;
+	struct address_space *mapping = file->f_mapping;
+	struct inode *inode = mapping->host;
 	struct fuse_file *ff = file->private_data;
 	struct fuse_conn *fc = ff->fm->fc;
 	size_t nmax = write ? fc->max_write : fc->max_read;
@@ -1440,6 +1441,7 @@ ssize_t fuse_direct_io(struct fuse_io_priv *io, struct iov_iter *iter,
 	int err = 0;
 	struct fuse_io_args *ia;
 	unsigned int max_pages;
+	bool fopen_direct_io = ff->open_flags & FOPEN_DIRECT_IO;
 
 	max_pages = iov_iter_npages(iter, fc->max_pages);
 	ia = fuse_io_alloc(io, max_pages);
@@ -1454,6 +1456,14 @@ ssize_t fuse_direct_io(struct fuse_io_priv *io, struct iov_iter *iter,
 			inode_unlock(inode);
 	}
 
+	if (fopen_direct_io && write) {
+		res = invalidate_inode_pages2_range(mapping, idx_from, idx_to);
+		if (res) {
+			fuse_io_free(ia);
+			return res;
+		}
+	}
+
 	io->should_dirty = !write && user_backed_iter(iter);
 	while (count) {
 		ssize_t nres;