Messages in this thread | | | Date | Tue, 21 Jun 2022 11:17:10 +0530 | Subject | Re: [PATCH rcu 02/12] rcu: Avoid tracing a few functions executed in stop machine | From | Neeraj Upadhyay <> |
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On 6/21/2022 3:50 AM, Paul E. McKenney wrote: > From: Patrick Wang <patrick.wang.shcn@gmail.com> > > Stop-machine recently started calling additional functions while waiting: > > ---------------------------------------------------------------- > Former stop machine wait loop: > do { > cpu_relax(); => macro > ... > } while (curstate != STOPMACHINE_EXIT); > ----------------------------------------------------------------- > Current stop machine wait loop: > do { > stop_machine_yield(cpumask); => function (notraced) > ... > touch_nmi_watchdog(); => function (notraced, inside calls also notraced) > ... > rcu_momentary_dyntick_idle(); => function (notraced, inside calls traced) > } while (curstate != MULTI_STOP_EXIT); > ------------------------------------------------------------------ > > These functions (and the functions that they call) must be marked > notrace to prevent them from being updated while they are executing. > The consequences of failing to mark these functions can be severe: > > rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: > rcu: 1-...!: (0 ticks this GP) idle=14f/1/0x4000000000000000 softirq=3397/3397 fqs=0 > rcu: 3-...!: (0 ticks this GP) idle=ee9/1/0x4000000000000000 softirq=5168/5168 fqs=0 > (detected by 0, t=8137 jiffies, g=5889, q=2 ncpus=4) > Task dump for CPU 1: > task:migration/1 state:R running task stack: 0 pid: 19 ppid: 2 flags:0x00000000 > Stopper: multi_cpu_stop+0x0/0x18c <- stop_machine_cpuslocked+0x128/0x174 > Call Trace: > Task dump for CPU 3: > task:migration/3 state:R running task stack: 0 pid: 29 ppid: 2 flags:0x00000000 > Stopper: multi_cpu_stop+0x0/0x18c <- stop_machine_cpuslocked+0x128/0x174 > Call Trace: > rcu: rcu_preempt kthread timer wakeup didn't happen for 8136 jiffies! g5889 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 > rcu: Possible timer handling issue on cpu=2 timer-softirq=594 > rcu: rcu_preempt kthread starved for 8137 jiffies! g5889 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=2 > rcu: Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior. > rcu: RCU grace-period kthread stack dump: > task:rcu_preempt state:I stack: 0 pid: 14 ppid: 2 flags:0x00000000 > Call Trace: > schedule+0x56/0xc2 > schedule_timeout+0x82/0x184 > rcu_gp_fqs_loop+0x19a/0x318 > rcu_gp_kthread+0x11a/0x140 > kthread+0xee/0x118 > ret_from_exception+0x0/0x14 > rcu: Stack dump where RCU GP kthread last ran: > Task dump for CPU 2: > task:migration/2 state:R running task stack: 0 pid: 24 ppid: 2 flags:0x00000000 > Stopper: multi_cpu_stop+0x0/0x18c <- stop_machine_cpuslocked+0x128/0x174 > Call Trace: > > This commit therefore marks these functions notrace: > rcu_preempt_deferred_qs() > rcu_preempt_need_deferred_qs() > rcu_preempt_deferred_qs_irqrestore() >
Only the preemptible RCU definitions are updated; so, this change is not required for non-preemptible RCU case?
Thanks Neeraj
> Signed-off-by: Patrick Wang <patrick.wang.shcn@gmail.com> > Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org> > Signed-off-by: Paul E. McKenney <paulmck@kernel.org> > --- > kernel/rcu/tree_plugin.h | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h > index c8ba0fe17267c..440d9e02a26e0 100644 > --- a/kernel/rcu/tree_plugin.h > +++ b/kernel/rcu/tree_plugin.h > @@ -460,7 +460,7 @@ static bool rcu_preempt_has_tasks(struct rcu_node *rnp) > * be quite short, for example, in the case of the call from > * rcu_read_unlock_special(). > */ > -static void > +static notrace void > rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags) > { > bool empty_exp; > @@ -581,7 +581,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags) > * is disabled. This function cannot be expected to understand these > * nuances, so the caller must handle them. > */ > -static bool rcu_preempt_need_deferred_qs(struct task_struct *t) > +static notrace bool rcu_preempt_need_deferred_qs(struct task_struct *t) > { > return (__this_cpu_read(rcu_data.cpu_no_qs.b.exp) || > READ_ONCE(t->rcu_read_unlock_special.s)) && > @@ -595,7 +595,7 @@ static bool rcu_preempt_need_deferred_qs(struct task_struct *t) > * evaluate safety in terms of interrupt, softirq, and preemption > * disabling. > */ > -static void rcu_preempt_deferred_qs(struct task_struct *t) > +static notrace void rcu_preempt_deferred_qs(struct task_struct *t) > { > unsigned long flags; >
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