Summary

Fixed-point divide/floor/ceil helpers trust callers never to pass zero divisor. Only guard is ASSERT() which in this tree is WARN_ON (os_types.h:76->asm/bug.h:43-49) non-blocking kprintf so execution falls through into div64_u64_rem/div64_s64 whose DragonFly implementations (linux/math64.h:57-61,75-80) emit literal C %// by zero. On x86_64 raises #DE (trap 0) kernel context panics. bw_frc_to_fixed line 69 ASSERT(denominator!=0) WARN_ON then line 74 div64_u64_rem(arg1_value,arg2_value,...) computes arg1%0 arg1/0 both fault when arg2_value==0. bw_floor2 (119) bw_ceil2 (132) compute div64_s64(arg.value abs_i64(significance.value)) with NO guard whatsoever significance.value==0->div64_s64(arg.value 0)->panic. Reachable via amdgpu KMOD; bw_* helpers invoked heavily by dce_calcs.c/dcn_calcs.c with denominators from display-mode params (pixel_rate hsr/vsr bytes_per_request lb_line_pitch...). Degenerate display mode or crafted EDID from hostile/malfunctioning external monitor at hotplug (unauthenticated monitor/dock/USB-C attack) or local privileged user DRM mode-set ioctls could route zero divisor. Impact DoS kernel panic no priv-esc no info-leak. End-to-end attacker reachability not proven from this file depends on caller validation in dce_calcs.c/dcn_calcs.c hence likely not certain.