Frequency of oscillator (exercise)
Your circuit is an "allpass oscillator".
The transfer function of the open loop is correct, in principle. However, the minus sign of the inverter is missing: -R2/R1.

As you can see, for w=1/T the remaining expression is -(R2/R1)(-2j/2j)=+1. Hence, the oscillation condition is fulfilled at w=1/RC. For a safe start of osillations, the inverter gain should be slightly larger than "-1" (for example: -1.1). The rising oscillation amplitudes will be hard-limited by the power supply rail, unless you include a soft-limiting device (two anti-parallel diodes across R2 - perhaps in series with another resistor).  

Explanation: Both blocks are first order allpass filters with a phase shift of -90deg at the frequency w=1/T per unit. Hence, the total phase shift at this frequency is -180deg. The inverter provides another -180deg and the phase condition (360deg resp. 0 deg) of the oscillation criterion is fulfilled at this frequency. The amplitude condition is fulfilled (theoretically) for R2=R1.