China need to improve in grain production ... I have no doubt that in a difficult time, grain export to China will be banned as well .. with any reason out of the blue
IIRC ... Russia should be the world's biggest exporter of grain such as wheat and Ukraine, which is controlled by Russia, is the other larger exporter of grain. No problem for China in that respect.
Rice, everyone seems to buy it from Thailand. Maybe even Vietnam would sell rice to China.
Corn is purchased from the Americans, but China produces a lot of corn. Soybeans come from America, Brazil, Argentina, whereas in the past, all soyabeans imported into China mostly came from America. Not anymore.
The Americans can ban their exports of foodstuffs to China, but China has others they can source things items from.