On Wed, 5 Apr 2017 12:39:28 -0700
"Paul E. McKenney" <paul...@linux.vnet.ibm.com> wrote:
> > Here's the crucial part of that stack dump again:
> >
> > save_stack_trace+0x1b/0x1d
> > check_stack+0xec/0x24a
> > stack_trace_call+0x40/0x53
> > 0xffffffffa0026077
> > ? ftrace_graph_caller+0x78/0xa8
> > ? trace_hardirqs_off+0xd/0xf
> > ? rcu_eqs_enter_common.constprop.71+0x5/0x108
> > rcu_eqs_enter_common.constprop.71+0x5/0x108
> > rcu_idle_enter+0x51/0x72
> >
> >
> > The stack trace was called on rcu_eqs_enter_common() inside the
> > rcu_idle_enter() function call.
> >
> > Perhaps if I just let rcu disable stack tracing? Something like this:
> >
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 50fee76..f894fc3 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -853,8 +853,10 @@ void rcu_idle_enter(void)
> > unsigned long flags;
> >
> > local_irq_save(flags);
> > + disable_stack_tracer();
> > rcu_eqs_enter(false);
> > rcu_sysidle_enter(0);
> > + enable_stack_tracer();
> > local_irq_restore(flags);
> > }
> > EXPORT_SYMBOL_GPL(rcu_idle_enter);
>
> That only covers one of two code paths, and still end up with the
> trace code thinking that RCU is paying attention to it when it really
> is not.
OK, that sounds like a separate bug to what I'm tracking.
>
> But if there is a disable_stack_tracer() and enable_stack_tracer(),
> I could use them as shown below. (Hand-edited patch, probably doesn't
> apply, let alone build.)
>
> Thanx, Paul
>
> ------------------------------------------------------------------------
>
> commit 1a11d6fd0ae344f7dccd57d3c587d9ef2a4bf08e
> Author: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> Date: Wed Apr 5 09:05:18 2017 -0700
>
> rcu: Fix dyntick-idle tracing
>
> The tracing subsystem started using rcu_irq_entry() and rcu_irq_exit()
> (with my blessing) to allow the current _rcuidle alternative tracepoint
> name to be dispensed with while still maintaining good performance.
> Unfortunately, this causes RCU's dyntick-idle entry code's tracing to
> appear to RCU like an interrupt that occurs where RCU is not designed
> to handle interrupts.
>
> This commit fixes this problem by moving the zeroing of ->dynticks_nesting
> after the offending trace_rcu_dyntick() statement, which narrows the
> window of vulnerability to a pair of adjacent statements that are now
> marked with comments to that effect.
>
> Reported-by: Steven Rostedt <rost...@goodmis.org>
> Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 50fee7689e71..7308c88ee57a 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -771,25 +771,24 @@ cpu_needs_another_gp(struct rcu_state *rsp, struct
> rcu_data *rdp)
> }
>
> /*
> - * rcu_eqs_enter_common - current CPU is moving towards extended quiescent
> state
> + * rcu_eqs_enter_common - current CPU is entering an extended quiescent state
> *
> - * If the new value of the ->dynticks_nesting counter now is zero,
> - * we really have entered idle, and must do the appropriate accounting.
> - * The caller must have disabled interrupts.
> + * Enter idle, doing appropriate accounting. The caller must have
> + * disabled interrupts.
> */
> -static void rcu_eqs_enter_common(long long oldval, bool user)
> +static void rcu_eqs_enter_common(bool user)
> {
> struct rcu_state *rsp;
> struct rcu_data *rdp;
> - RCU_TRACE(struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);)
> + struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
>
> - trace_rcu_dyntick(TPS("Start"), oldval, rdtp->dynticks_nesting);
> + trace_rcu_dyntick(TPS("Start"), rdtp->dynticks_nesting, 0);
> if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
> !user && !is_idle_task(current)) {
> struct task_struct *idle __maybe_unused =
> idle_task(smp_processor_id());
>
> - trace_rcu_dyntick(TPS("Error on entry: not idle task"), oldval,
> 0);
> + trace_rcu_dyntick(TPS("Error on entry: not idle task"),
> rdtp->dynticks_nesting, 0);
> rcu_ftrace_dump(DUMP_ORIG);
> WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
> current->pid, current->comm,
> @@ -800,7 +799,8 @@ static void rcu_eqs_enter_common(long long oldval, bool
> user)
> do_nocb_deferred_wakeup(rdp);
> }
> rcu_prepare_for_idle();
> - rcu_dynticks_eqs_enter();
> + disable_stack_tracer();
> + rdtp->dynticks_nesting = 0; /* Breaks tracing momentarily. */
> + rcu_dynticks_eqs_enter(); /* After this, tracing works again. */
> + enable_stack_tracer();
OK, do you want me to send you a patch, or should I take your patch
into my tree and add this?
-- Steve
> rcu_dynticks_task_enter();
>
> /*
> @@ -821,19 +821,15 @@ static void rcu_eqs_enter_common(long long oldval, bool
> user)
> */
> static void rcu_eqs_enter(bool user)
> {
> - long long oldval;
> struct rcu_dynticks *rdtp;
>
> rdtp = this_cpu_ptr(&rcu_dynticks);
> - oldval = rdtp->dynticks_nesting;
> WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
> - (oldval & DYNTICK_TASK_NEST_MASK) == 0);
> - if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) {
> - rdtp->dynticks_nesting = 0;
> - rcu_eqs_enter_common(oldval, user);
> - } else {
> + (rdtp->dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0);
> + if ((rdtp->dynticks_nesting & DYNTICK_TASK_NEST_MASK) ==
> DYNTICK_TASK_NEST_VALUE)
> + rcu_eqs_enter_common(user);
> + else
> rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
> - }
> }
>
> /**
> @@ -892,19 +888,18 @@ void rcu_user_enter(void)
> */
> void rcu_irq_exit(void)
> {
> - long long oldval;
> struct rcu_dynticks *rdtp;
>
> RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_irq_exit() invoked with irqs
> enabled!!!");
> rdtp = this_cpu_ptr(&rcu_dynticks);
> - oldval = rdtp->dynticks_nesting;
> - rdtp->dynticks_nesting--;
> WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
> - rdtp->dynticks_nesting < 0);
> - if (rdtp->dynticks_nesting)
> - trace_rcu_dyntick(TPS("--="), oldval, rdtp->dynticks_nesting);
> - else
> - rcu_eqs_enter_common(oldval, true);
> + rdtp->dynticks_nesting < 1);
> + if (rdtp->dynticks_nesting <= 1) {
> + rcu_eqs_enter_common(true);
> + } else {
> + trace_rcu_dyntick(TPS("--="), rdtp->dynticks_nesting,
> rdtp->dynticks_nesting - 1);
> + rdtp->dynticks_nesting--;
> + }
> rcu_sysidle_enter(1);
> }
>
