On Wed, Sep 02, 2015 at 03:10:04PM -0700, Philipp Schrader wrote: > On Wed, Sep 2, 2015 at 12:38 PM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > On Tue, 1 Sep 2015 17:35:23 +0200 (CEST) > > Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > > >> On Mon, 31 Aug 2015, Philipp Schrader wrote: > > >> > rcu_dereference_check() usage! > >> > [ 0.055093] > >> > [ 0.055093] other info that might help us debug this: > >> > [ 0.055093] > >> > [ 0.055097] > >> > [ 0.055097] RCU used illegally from idle CPU! > >> > [ 0.055097] rcu_scheduler_active = 1, debug_locks = 1 > >> > [ 0.055100] RCU used illegally from extended quiescent state! > >> > [ 0.055104] no locks held by swapper/0/0. > >> > [ 0.055106] > >> > [ 0.055106] stack backtrace: > >> > [ 0.055112] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.1.6+ #2 > >> > [ 0.055116] Hardware name: Generic DRA74X (Flattened Device Tree) > >> > [ 0.055130] [<c00196b8>] (unwind_backtrace) from [<c001515c>] > >> > (show_stack+0x20/0x24) > >> > [ 0.055146] [<c001515c>] (show_stack) from [<c07bc408>] > >> > (dump_stack+0x84/0xa0) > >> > [ 0.055160] [<c07bc408>] (dump_stack) from [<c009bc38>] > >> > (lockdep_rcu_suspicious+0xb0/0x110) > >> > [ 0.055172] [<c009bc38>] (lockdep_rcu_suspicious) from [<c01246c4>] > >> > (time_hardirqs_off+0x2b8/0x3c8) > >> > [ 0.055184] [<c01246c4>] (time_hardirqs_off) from [<c009a218>] > >> > (trace_hardirqs_off_caller+0x2c/0xf4) > >> > [ 0.055194] [<c009a218>] (trace_hardirqs_off_caller) from > >> > [<c009a2f4>] (trace_hardirqs_off+0x14/0x18) > >> > [ 0.055204] [<c009a2f4>] (trace_hardirqs_off) from [<c00c7ecc>] > >> > (rcu_idle_enter+0x78/0xcc) > >> > [ 0.055213] [<c00c7ecc>] (rcu_idle_enter) from [<c0093eb0>] > >> > (cpu_startup_entry+0x190/0x518) > >> > [ 0.055222] [<c0093eb0>] (cpu_startup_entry) from [<c07b95b4>] > >> > (rest_init+0x13c/0x17c) > >> > [ 0.055231] [<c07b95b4>] (rest_init) from [<c0b32c74>] > >> > (start_kernel+0x320/0x380) > >> > [ 0.055238] [<c0b32c74>] (start_kernel) from [<8000807c>] (0x8000807c) > >> > > >> > I'm not sure how to debug this; I'm still reading up on RCUs. Pretty > >> > nifty ideas. > >> > > >> > Looking at include/trace/events/hist.h it appears line 31 is the end > >> > of a TRACE_EVENT macro usage. > >> > Does that mean the macro is using RCU improperly somehow? > > > > I think this needs to be a trace_*_rcu_idle() call. That is, I bet the > > tracepoint was triggered when rcu wasn't watching. > > Thank you for your reply Steve. > I've got the following patch now that makes the splat disappear: > > diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c > index aaade2e..d0e1d0e 100644 > --- a/kernel/trace/trace_irqsoff.c > +++ b/kernel/trace/trace_irqsoff.c > @@ -450,7 +450,7 @@ EXPORT_SYMBOL_GPL(stop_critical_timings); > #ifdef CONFIG_PROVE_LOCKING > void time_hardirqs_on(unsigned long a0, unsigned long a1) > { > - trace_preemptirqsoff_hist(IRQS_ON, 0); > + trace_preemptirqsoff_hist_rcuidle(IRQS_ON, 0); > if (!preempt_trace() && irq_trace()) > stop_critical_timing(a0, a1); > } > @@ -459,7 +459,7 @@ void time_hardirqs_off(unsigned long a0, unsigned long a1) > { > if (!preempt_trace() && irq_trace()) > start_critical_timing(a0, a1); > - trace_preemptirqsoff_hist(IRQS_OFF, 1); > + trace_preemptirqsoff_hist_rcuidle(IRQS_OFF, 1); > } > > #else /* !CONFIG_PROVE_LOCKING */ > > Does that look reasonable? > Or could this cause a problem down the road? Looks good to me! > Still reading up on RCUs and how they work. Me too. ;-) Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html