Can a defendant avoid liability by claiming that he did not have the requisite knowledge of a substantial risk of harm?

Whether a defendant had requisite knowledge of a substantial risk of harm is a question of fact. Farmer, 511 U.S. at 842. Thus, liability may be avoided by presenting evidence that the defendant lacked knowledge of the risk and/or that his response was reasonable in light of all the circumstances. See Farmer, 511 U.S. at 844-45; see also Simmons v. Navajo County Ariz. 609 F.3d 1011, 1017-18 (9th Cir. 2010) (requiring official be subjectively aware of serious medical need and fail to adequately respond to need to establish deliberate indifference). "Mere negligent failure to protect an inmate from harm is not actionable under Section 1983. Farmer, 511 U.S. at 835.