Explain what is the problem with this implementation of the one-writer many-readers problem?

int readcount; Semaphore mutex, wrt; // shared and initialized to 0 // shared and initialized to 1; // Writer: // Readers semWait (mutex) readcount readcount 1; if readcount 1 then semWait (wrt); semSignal (mutex); /*reading performed/ semWait (mutex); readcount :- readcount 1; if readcount0 then Up (wrt) semSignal (mutex); semWait (wrt); /* Writing performed/ semSignal (wrt)