Hello Steve, I've faced the following RCU warning while I ran ftracetest testcase "ftrace - function graph filters with stack tracer" on qemu. The kernel is ftrace/core branch. [ 10.919174] ============================= [ 10.920077] WARNING: suspicious RCU usage [ 10.920977] 4.12.0-rc5+ #1 Not tainted [ 10.921828] ----------------------------- [ 10.922748] /home/mhiramat/ksrc/linux/include/trace/events/rcu.h:454 suspicious rcu_dereference_check() usage! [ 10.924761] [ 10.924761] other info that might help us debug this: [ 10.924761] [ 10.926775] [ 10.926775] RCU used illegally from idle CPU! [ 10.926775] rcu_scheduler_active = 2, debug_locks = 1 [ 10.929176] RCU used illegally from extended quiescent state! [ 10.930525] no locks held by swapper/7/0. [ 10.931547] [ 10.931547] stack backtrace: [ 10.932777] CPU: 7 PID: 0 Comm: swapper/7 Not tainted 4.12.0-rc5+ #1 [ 10.934025] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.3-1.fc25 04/01/2014 [ 10.935869] Call Trace: [ 10.936550] dump_stack+0x86/0xcf [ 10.937359] lockdep_rcu_suspicious+0xc5/0x100 [ 10.938327] ? rcu_eqs_exit_common.isra.53+0x5/0x150 [ 10.939229] rcu_irq_enter+0x18d/0x1a0 [ 10.939902] ? rcu_eqs_exit_common.isra.53+0x5/0x150 [ 10.940683] check_stack+0xbb/0x2f0 [ 10.941333] stack_trace_call+0x3f/0x50 [ 10.942010] 0xffffffffa0000077 [ 10.942620] ? ftrace_graph_caller+0x78/0xa8 [ 10.943342] ? rcu_eqs_exit_common.isra.53+0x5/0x150 [ 10.944214] ? rcu_idle_exit+0x5/0x90 [ 10.944937] rcu_eqs_exit_common.isra.53+0x5/0x150 [ 10.945754] rcu_idle_exit+0x8c/0x90 [ 10.946612] ? rcu_eqs_exit_common.isra.53+0x5/0x150 [ 10.947414] ? rcu_idle_exit+0x8c/0x90 [ 10.948091] do_idle+0x116/0x1c0 [ 10.948797] cpu_startup_entry+0x1d/0x20 [ 10.949569] start_secondary+0xfa/0x100 [ 10.950335] secondary_startup_64+0x9f/0x9f [ 10.951182] I attached full log and kconfig. I can reproduce it with just running following script. ---- cd tools/testing/selftests/ftrace while true; do ./ftracetest test.d/ftrace/fgraph-filter-stack.tc done ---- Thank you, -- Masami Hiramatsu