linux-kernel - Re: [RFC PATCH v3 1/5] tracing: Introduce faultable tracepoints (v3)

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Date:   Tue, 3 Oct 2023 13:37:26 -0400
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     paulmck@...nel.org, Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org,
        Michael Jeanson <mjeanson@...icios.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Yonghong Song <yhs@...com>, Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>, bpf@...r.kernel.org,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [RFC PATCH v3 1/5] tracing: Introduce faultable tracepoints (v3)

On 10/3/23 13:33, Paul E. McKenney wrote:
> On Tue, Oct 03, 2023 at 10:08:54AM -0400, Steven Rostedt wrote:
>> On Tue, 3 Oct 2023 06:44:50 -0700
>> "Paul E. McKenney" <paulmck@...nel.org> wrote:
>>
>>>> That way it is clear what uses what, as I read the original paragraph a
>>>> couple of times and could have sworn that rcu_read_lock_trace() required
>>>> tasks to not block.
>>>
>>> That would work for me.  Would you like to send a patch, or would you
>>> rather we made the adjustments?
>>
>> Which ever.
> 
> OK, how about like this?
> 
> 							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> commit 973eb79ec46c16f13bb5b47ad14d44a1f1c79dc9
> Author: Paul E. McKenney <paulmck@...nel.org>
> Date:   Tue Oct 3 10:30:01 2023 -0700
> 
>      doc: Clarify RCU Tasks reader/updater checklist
>      
>      Currently, the reader/updater compatibility rules for the three RCU
>      Tasks flavors are squished together in a single paragraph, which can
>      result in confusion.  This commit therefore splits them out into a list,
>      clearly showing the distinction between these flavors.
>      

Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

Thanks!

Mathieu

>      Reported-by: Steven Rostedt <rostedt@...dmis.org>
>      Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> 
> diff --git a/Documentation/RCU/checklist.rst b/Documentation/RCU/checklist.rst
> index bd3c58c44bef..c432899aff22 100644
> --- a/Documentation/RCU/checklist.rst
> +++ b/Documentation/RCU/checklist.rst
> @@ -241,15 +241,22 @@ over a rather long period of time, but improvements are always welcome!
>   	srcu_struct.  The rules for the expedited RCU grace-period-wait
>   	primitives are the same as for their non-expedited counterparts.
>   
> -	If the updater uses call_rcu_tasks() or synchronize_rcu_tasks(),
> -	then the readers must refrain from executing voluntary
> -	context switches, that is, from blocking.  If the updater uses
> -	call_rcu_tasks_trace() or synchronize_rcu_tasks_trace(), then
> -	the corresponding readers must use rcu_read_lock_trace() and
> -	rcu_read_unlock_trace().  If an updater uses call_rcu_tasks_rude()
> -	or synchronize_rcu_tasks_rude(), then the corresponding readers
> -	must use anything that disables preemption, for example,
> -	preempt_disable() and preempt_enable().
> +	Similarly, it is necssary to correctly use the RCU Tasks flavors:
> +
> +	a.	If the updater uses synchronize_rcu_tasks() or
> +		call_rcu_tasks(), then the readers must refrain from
> +		executing voluntary context switches, that is, from
> +		blocking.
> +
> +	b.	If the updater uses call_rcu_tasks_trace()
> +		or synchronize_rcu_tasks_trace(), then the
> +		corresponding readers must use rcu_read_lock_trace()
> +		and rcu_read_unlock_trace().
> +
> +	c.	If an updater uses call_rcu_tasks_rude() or
> +		synchronize_rcu_tasks_rude(), then the corresponding
> +		readers must use anything that disables preemption,
> +		for example, preempt_disable() and preempt_enable().
>   
>   	Mixing things up will result in confusion and broken kernels, and
>   	has even resulted in an exploitable security issue.  Therefore,

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com