What constitutes cruel and unusual punishment under the Eighth Amendment?

"After incarceration, only the unnecessary and wanton infliction of pain ... constitutes cruel and unusual punishment forbidden by the Eighth Amendment. To be cruel and unusual punishment, conduct that does not purport to be punishment at all must involve more than ordinary lack of due care for the prisoner's interest or safety." Whitley v. Albers, 475 U.S. 312, 319 (1986). Whether security measures inflict unnecessary and wanton pain and suffering depends on whether the force was applied in a good faith effort to maintain or restore discipline or maliciously and sadistically for the very purpose of causing harm. Id. at 320-21 (quotation omitted).