Re: [PATCH v2 1/7] sched/fair: Fix zero_vruntime tracking

[John Stultz]

On Sat, Mar 28, 2026 at 10:03 AM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> On Fri, 27 Mar 2026 22:44:28 -0700
> John Stultz <jstultz@xxxxxxxxxx> wrote:
>
> > I'll continue digging next week on this, but wanted to share in case
> > anyone else sees something obvious first.
>
> FYI, you can add a trace_printk() around all the areas that assign
> cfs_rq->curr, and if you use the persistent ring buffer you can retrieve
> the output of all the events that lead up to the crash.
>
> Add to the kernel command line:
>
>    reserve_mem=100M:12M:trace trace_instance=boot_mapped^traceprintk^traceoff@trace
>
> And before starting your testing:
>
>   echo 1 > /sys/kernel/tracing/instances/boot_mapped/tracing_on
>
> If all goes well, after the crash you should see the output in:
>
>   cat /sys/kernel/tracing/instances/boot_mapped/trace

Nice. I've actually been using ftrace_dump_on_oops as I log the VM
serial console to a file and don't have to remember to go fetch it out
the next time. But this is helpful when its on real hardware (dumping
the trace over serial console can take awhile and I've had cases where
the hardware watchdogs reboot the device midway when the trace is too
large).

thanks
-john