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Message-ID: <70238b0a-de88-c4b6-ba46-22754d8e7b48@quicinc.com>
Date:   Wed, 22 Jun 2022 21:19:25 +0530
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Subject: Re: [PATCH rcu 02/12] rcu: Avoid tracing a few functions executed in
 stop machine
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To:     <paulmck@kernel.org>
CC:     <rcu@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <kernel-team@fb.com>, <rostedt@goodmis.org>,
        Patrick Wang <patrick.wang.shcn@gmail.com>
References: <20220620222022.GA3839466@paulmck-ThinkPad-P17-Gen-1>
 <20220620222032.3839547-2-paulmck@kernel.org>
 <9de7f497-a4cd-ebdb-e912-d4cd73b4a982@quicinc.com>
 <20220621222147.GR1790663@paulmck-ThinkPad-P17-Gen-1>
 <95e12a75-72c6-76c7-26cc-a24af1e8cce0@quicinc.com>
 <20220622153506.GY1790663@paulmck-ThinkPad-P17-Gen-1>
From:   Neeraj Upadhyay <quic_neeraju@quicinc.com>
In-Reply-To: <20220622153506.GY1790663@paulmck-ThinkPad-P17-Gen-1>
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On 6/22/2022 9:05 PM, Paul E. McKenney wrote:
> On Wed, Jun 22, 2022 at 05:20:35PM +0530, Neeraj Upadhyay wrote:
>>
>>
>> On 6/22/2022 3:51 AM, Paul E. McKenney wrote:
>>> On Tue, Jun 21, 2022 at 11:17:10AM +0530, Neeraj Upadhyay wrote:
>>>>
>>>>
>>>> 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?
>>>
>>> It appears to me to be required.  How about as shown below?
>>>
>>
>> Looks good to me.
> 
> Thank you!  May I apply your Reviewed-by to both of these?  (1/12 and
> 2/12.)
> 

Yes, sure.

Reviewed-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>


Thanks
Neeraj

> 							Thanx, Paul
> 
>> Thanks
>> Neeraj
>>
>>> 							Thanx, Paul
>>>
>>> ------------------------------------------------------------------------
>>>
>>> commit 06cfe0c675c93884c3ffc75ec24ece7d0acd7a32
>>> Author: Patrick Wang <patrick.wang.shcn@gmail.com>
>>> Date:   Tue Apr 26 18:45:02 2022 +0800
>>>
>>>       rcu: Avoid tracing a few functions executed in stop machine
>>>       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()
>>>       [ paulmck: Apply feedback from Neeraj Upadhyay. ]
>>>       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>
>>>
>>> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
>>> index c8ba0fe17267c..7a07f2ca153e2 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;
>>> @@ -926,7 +926,7 @@ static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
>>>     * Because there is no preemptible RCU, there can be no deferred quiescent
>>>     * states.
>>>     */
>>> -static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
>>> +static notrace bool rcu_preempt_need_deferred_qs(struct task_struct *t)
>>>    {
>>>    	return false;
>>>    }
>>> @@ -935,7 +935,7 @@ static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
>>>    // period for a quiescent state from this CPU.  Note that requests from
>>>    // tasks are handled when removing the task from the blocked-tasks list
>>>    // below.
>>> -static void rcu_preempt_deferred_qs(struct task_struct *t)
>>> +static notrace void rcu_preempt_deferred_qs(struct task_struct *t)
>>>    {
>>>    	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);