On Sat, Apr 17, 2021 at 9:41 PM Cong Wang [off-list ref] wrote:

From: Cong Wang <redacted>

We hit a divide error in rwb_arm_timer() and crash dump shows
rqd->scale_step is 16777215 (0xffffff in hex), so the expression
"(rqd->scale_step + 1) << 8)" is 0x100000000, which is just beyond
32-bit integer range, hence it is truncated to 0 and int_sqrt(0)
returns 0 too, so we end up passing 0 as a divisor to div_u64().

Never mind. rqd->scale_step should be capped by
rq_depth_scale_down(), so should never be so large. In the old
calc_wb_limits() implementation, rwb->wb_max was set to zero
accidentally.

Thanks.