A Study Evaluating Safety and Efficacy of Obinutuzumab, Polatuzumab Vedotin (Pola), and Atezolizumab (Atezo) in Participants With Relapsed or Refractory Follicular Lymphoma (FL) and Rituximab, Atezo, and Pola in Participants With Relapsed or Refractory Diffuse Large B-Cell Lymphoma (DLBCL)

"Atezolizumab will be administered by intravenous (IV) infusion at a flat dose of 1200 milligram (mg) every 3 weeks (Q3W) on Day 1 of Cycles 2-6, given in 21-day cycles during induction treatment.~NOTE: Atezolizumab treatment has been discontinued in all participants currently on study treatment."

Obinutuzumab will be administered by IV infusion at a flat dose of 1000 mg on Days 1, 8, and 15 of Cycle 1, and on Day 1 of Cycles 2-6, given in 21-day cycles during induction treatment, and on Day 1 of every other month during maintenance treatment (1 cycle=21 days; infusion rate starts at 50 mg/hour (hr) and increases every 30 min to a maximum of 400 mg/hr).

Polatuzumab vedotin will be administered by IV infusion. For relapsed or refractory FL either 1.4 mg/kilogram (kg) or 1.8 mg/kg (dose-escalation phase) and at RP2D (dose-expansion phase) on Day 1 of Cycles 1-6 will be given in 21-day cycles during induction treatment. For relapsed or refactory DLBCL, 1.8 mg/kg will be given during run-in phase and either 1.8 mg/kg or 1.4 mg/kg during the expansion phase (1 cycle=21 days; infusion rate starts with 90 min and decreases to 30 min).

Rituximab will be administered by IV infusion at 375 mg/m˄2 on Day 1 of Cycles 1-6 during induction treatment (1 cycle-21 days; infusion rate starts with 50 mg/hr and increases every 30 min to a maximum of 400 mg/hr).