Checking if a polynomial factors into linear factors
As far as I know, the best algorithm we have currently to check if $f$ (given by an arithmetic circuit) can be factorized into linear factors is via the randomized algorithm of Kaltofen (PDF) which actually produces blackboxes for all the irreducible factors of $f$, and works over any large enough field. In fact, this problem of polynomial factorization for general circuits was recently shown by Kopparty, Saraf and Shpilka to be equivalent to the problem of blackbox-PIT for general circuits. 

As mentioned by Bruno, if you are interested in checking a the given circuit is divisible by a given $\ell$, then this reduces to a specific PIT problem. We don't know how to do this deterministically in general but I know of one special case where we know how to do this PIT. There is a deterministic poly-time algorithm (PDF) to check if a given $\ell$ divides a given sparse polynomial $f$. 

(Another trivial special case when $f$ is given by a bounded top fan-in depth three circuit. There, $f \bmod \ell$ is also a bounded fan-in depth three circuit and we know how to do PIT in deterministic polynomial time.)