On Wed, Jul 23, 2025 at 04:34:50PM -0400, Steven Rostedt wrote:
> On Wed, 23 Jul 2025 13:27:54 -0700
> "Paul E. McKenney" <[email protected]> wrote:
>
> > This triggers continues to trigger a kernel test robot report of a
> > "using smp_processor_id() in preemptible" splat. I looked for issues
> > with explicit preemption disabling, and, not finding any, will next turn
> > my attention to accesses to per-CPU variables. Any and all insights
> > are welcome.
>
> Currently perf and ftrace expect the tracepoints to be called with
> preemption disabled. You may need this:
>
> diff --git a/include/trace/perf.h b/include/trace/perf.h
> index a1754b73a8f5..1b7925a85966 100644
> --- a/include/trace/perf.h
> +++ b/include/trace/perf.h
> @@ -71,7 +71,9 @@ perf_trace_##call(void *__data, proto)
> \
> u64 __count __attribute__((unused)); \
> struct task_struct *__task __attribute__((unused)); \
> \
> + preempt_disable_notrace(); \
> do_perf_trace_##call(__data, args); \
> + preempt_enable_notrace(); \
> }
>
> #undef DECLARE_EVENT_SYSCALL_CLASS
> diff --git a/include/trace/trace_events.h b/include/trace/trace_events.h
> index 4f22136fd465..0504a423ca25 100644
> --- a/include/trace/trace_events.h
> +++ b/include/trace/trace_events.h
> @@ -436,7 +436,9 @@ __DECLARE_EVENT_CLASS(call, PARAMS(proto), PARAMS(args),
> PARAMS(tstruct), \
> static notrace void \
> trace_event_raw_event_##call(void *__data, proto) \
> { \
> + preempt_disable_notrace(); \
> do_trace_event_raw_event_##call(__data, args); \
> + preempt_enable_notrace(); \
> }
>
> #undef DECLARE_EVENT_SYSCALL_CLASS
>
>
> But please add it with the change, as there's "preempt_count" accounting to
> report to the user that accounts that preemption was disabled when called.
Thank you, Steve! I suspect that it would have taken me one good long
time to find that one, like maybe forever. ;-)
I am doing local testing, then will expose it to the kernel test robot,
and if all goes well, fold it in with attribution.
Thanx, Paul
