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

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Message-ID: <2ba5baa2-3598-4499-bd88-b7fc139f6ad8@paulmck-laptop>
Date:   Tue, 3 Oct 2023 11:15:21 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        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 Tue, Oct 03, 2023 at 01:38:56PM -0400, Steven Rostedt wrote:
> On Tue, 3 Oct 2023 10:33:33 -0700
> "Paul E. McKenney" <paulmck@...nel.org> 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?
> 
> Reviewed-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> 
> Link: https://lore.kernel.org/all/20231002211936.5948253e@gandalf.local.home/

Thank you both!  Updated as shown below.

						Thanx, Paul

------------------------------------------------------------------------

commit 4d2115e8919760c690e30f48cae2f017c1581546
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.
    
    Link: https://lore.kernel.org/all/20231002211936.5948253e@gandalf.local.home/
    
    Reported-by: Steven Rostedt <rostedt@...dmis.org>
    Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
    Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
    Reviewed-by: Steven Rostedt (Google) <rostedt@...dmis.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,