Tracepoints use RCU for protection and they must not be called on offline CPUS. So make this tracepoint conditional. Otherwise it can produce the following warning:
=============================== [ INFO: suspicious RCU usage. ] 4.5.0-rc7-next-20160308 #44 Not tainted ------------------------------- include/trace/events/ipi.h:35 suspicious rcu_dereference_check() usage! other info that might help us debug this: RCU used illegally from offline CPU! rcu_scheduler_active = 1, debug_locks = 1 no locks held by swapper/3/0. stack backtrace: CPU: 3 PID: 0 Comm: swapper/3 Not tainted 4.5.0-rc7-next-20160308 #44 Hardware name: ARM Juno development board (r2) (DT) Call trace: dump_backtrace+0x0/0x218 show_stack+0x24/0x30 dump_stack+0xb4/0xf0 lockdep_rcu_suspicious+0xd0/0x118 smp_cross_call+0x1a8/0x1b0 arch_send_call_function_single_ipi+0x3c/0x48 generic_exec_single+0xc0/0x178 smp_call_function_single+0xec/0x1b8 cpuhp_report_idle_dead+0x70/0x88 cpu_startup_entry+0x358/0x3c0 secondary_start_kernel+0x190/0x1e8 Cc: Steven Rostedt <[email protected]> Cc: Ingo Molnar <[email protected]> Signed-off-by: Sudeep Holla <[email protected]> --- include/trace/events/ipi.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) Hi Steven, I observed that in "include/linux/tracepoint.h", we have #define __DO_TRACE(tp, proto, args, cond, prercu, postrcu) ... if (!cpu_online(raw_smp_processor_id())) return; if (!(cond)) return; ... where !cond check seems reduntant if it's cpu_online check. So, does this patch handle the warning correctly or is there any better way ? I did see few traces with same condition, just thought of checking with you. Regards, Sudeep diff --git a/include/trace/events/ipi.h b/include/trace/events/ipi.h index 834a7362a610..d8ca2f2e24ac 100644 --- a/include/trace/events/ipi.h +++ b/include/trace/events/ipi.h @@ -15,12 +15,14 @@ * It is necessary for @reason to be a static string declared with * __tracepoint_string. */ -TRACE_EVENT(ipi_raise, +TRACE_EVENT_CONDITION(ipi_raise, TP_PROTO(const struct cpumask *mask, const char *reason), TP_ARGS(mask, reason), + TP_CONDITION(cpu_online(raw_smp_processor_id())), + TP_STRUCT__entry( __bitmask(target_cpus, nr_cpumask_bits) __field(const char *, reason) -- 1.9.1
