On Wed, 27 Apr 2016, John Syne wrote: > I’m attempting to add DMA support to the ti_am335x_adc driver but when > running the Lauterback debugger, I get strange timer corruption and the > kernel completely loops forever in include/linux/math64.h and takes the > “bhi” branch below and never gets to C00BB2A0. > So here is what I see after single stepping and running and stopping several > times. As you can see, the timer is negative and this is causing a lockup. I > have seen the same occur with timekeeping_get_ns where delta is negative ( > tkr->cycle_last occurs after cycle_now) . Seems like a race condition. Does It's not a race condition. By stopping the kernel you make the clocksource wrap around resulting in a negative delta. > anyone have any idea as to why this would be happening, or alternatively, > how can I just cleanup this up when I get a negative value. I tried setting > tkr->cycle_last = cycle_now, but that didn’t work. Enabling CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE should fix that issue. Thanks, tglx
