You will have to make tese routines reentrant. There is a different approach for the generated module's functions and your own routines (if you have got some) that are called from different places, within a handler and from main() directly or indirectly.
for the latter case you may use the keyword "reentrant" while the other references have to be kept in a file.
Left click on your project in the Workspace Explorer window, select Add New Item and choose "Keil Reentrancy File".
Here you name all the functions you want to be reentrant, one item per line, case sensitive, no parenthesis, no parameters.