linux-kernel - Re: [PATCH RFC v2 tip/core/rcu 14/22] rcu-tasks: Add an RCU Tasks Trace to simplify protection of tracing hooks

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Date:   Sat, 28 Mar 2020 10:06:35 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
        oleg@...hat.com, Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Andrii Nakryiko <andriin@...com>
Subject: Re: [PATCH RFC v2 tip/core/rcu 14/22] rcu-tasks: Add an RCU Tasks
 Trace to simplify protection of tracing hooks

On Thu, Mar 19, 2020 at 07:41:53PM -0700, Paul E. McKenney wrote:
> On Thu, Mar 19, 2020 at 08:48:38PM -0400, Steven Rostedt wrote:
> > On Thu, 19 Mar 2020 17:28:13 -0700
> > "Paul E. McKenney" <paulmck@...nel.org> wrote:
> > 
> > > Good point.  If interrupts are disabled, it will need to use some
> > > other mechanism.  One approach is irqwork.  Another is a timer.
> > > 
> > > Suggestions?
> > 
> > Ftrace and perf use irq_work, I would think that should work here too.
> 
> Sounds good, will give it a go!  And thank you for catching this!

Since the the Tasks-RCU holdout thread is supposed to wake up periodically to
scan holdout tasks anyway, can it not detect the end of the Trace-RCU grace
period on its next wake up? Sorry if I missed something.

thanks,

 - Joel