Re: [PATCH 0/6] Switch __DECLARE_TRACE() to new notrace variant of SRCU-fast

[Steven Rostedt]

On Wed, 23 Jul 2025 13:27:54 -0700
"Paul E. McKenney" <paul...@kernel.org> 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.

-- Steve