  We consider a reversal of the magnetic moment of a nano-magnet by the
fluctuating spin-torque induced by a non-equilibrium current of electron spins.
This is an example of the problem of the escape of a particle from a metastable
state subjected to a fluctuating non-conservative force. The spin-torque is the
non-conservative force and its fluctuations are beyond the description of the
fluctuation-dissipation theorem. We estimate the joint probability distribution
of work done by the spin torque and the Joule heat generated by the current,
which satisfies the fluctuation theorem for a small engine. We predict a
threshold voltage above which the spin-torque shot noise induces probabilistic
switching events and below which such events are blocked. We adopt the theory
of the full-counting statistics under the adiabatic pumping of spin angular
momentum. This enables us to account for the backaction effect, which is
crucial to maintain consistency with the fluctuation theorem.
