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Date:   Tue, 5 May 2020 15:24:29 -0700
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        Andy Lutomirski <luto@kernel.org>,
        Alexandre Chartre <alexandre.chartre@oracle.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Joel Fernandes <joel@joelfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        Brian Gerst <brgerst@gmail.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Will Deacon <will@kernel.org>
Subject: Re: [patch V4 part 3 11/29] rcu: Provide rcu_irq_exit_preempt()
Message-ID: <20200505222428.GU2869@paulmck-ThinkPad-P72>
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On Wed, May 06, 2020 at 12:05:04AM +0200, Thomas Gleixner wrote:
> "Paul E. McKenney" <paulmck@kernel.org> writes:
> 
> > On Tue, May 05, 2020 at 03:44:05PM +0200, Thomas Gleixner wrote:
> >> Interrupts and exceptions invoke rcu_irq_enter() on entry and need to
> >> invoke rcu_irq_exit() before they either return to the interrupted code or
> >> invoke the scheduler due to preemption.
> >> 
> >> The general assumption is that RCU idle code has to have preemption
> >> disabled so that a return from interrupt cannot schedule. So the return
> >> from interrupt code invokes rcu_irq_exit() and preempt_schedule_irq().
> >> 
> >> If there is any imbalance in the rcu_irq/nmi* invocations or RCU idle code
> >> had preemption enabled then this goes unnoticed until the CPU goes idle or
> >> some other RCU check is executed.
> >> 
> >> Provide rcu_irq_exit_preempt() which can be invoked from the
> >> interrupt/exception return code in case that preemption is enabled. It
> >> invokes rcu_irq_exit() and contains a few sanity checks in case that
> >> CONFIG_PROVE_RCU is enabled to catch such issues directly.
> >> 
> >> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> >> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> >> Cc: Joel Fernandes <joel@joelfernandes.org>
> >
> > The ->dynticks_nmi_nesting field is going away at some point, but
> > there is always "git merge".  ;-)
> 
> Yes. The logistics for merging all of this is going to be interesting :)

;-) ;-) ;-)

						Thanx, Paul