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Date: Wed, 13 May 2020 22:46:51 -0400 From: Joel Fernandes <joel@...lfernandes.org> To: Thomas Gleixner <tglx@...utronix.de> Cc: LKML <linux-kernel@...r.kernel.org>, x86@...nel.org, "Paul E. McKenney" <paulmck@...nel.org>, Andy Lutomirski <luto@...nel.org>, Alexandre Chartre <alexandre.chartre@...cle.com>, Frederic Weisbecker <frederic@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson <sean.j.christopherson@...el.com>, Masami Hiramatsu <mhiramat@...nel.org>, Petr Mladek <pmladek@...e.com>, Steven Rostedt <rostedt@...dmis.org>, Boris Ostrovsky <boris.ostrovsky@...cle.com>, Juergen Gross <jgross@...e.com>, Brian Gerst <brgerst@...il.com>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Josh Poimboeuf <jpoimboe@...hat.com>, Will Deacon <will@...nel.org> Subject: Re: [patch V4 part 3 11/29] rcu: Provide rcu_irq_exit_preempt() On Wed, May 13, 2020 at 10:41:16PM -0400, Joel Fernandes wrote: > Hi Thomas, > > On Tue, May 05, 2020 at 03:44:05PM +0200, Thomas Gleixner wrote: > > Thank you for CC'ing me. > > > 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. > > Could you let me know which patch or part in the multi-part series is using it? Ah I see its "x86/entry/common: Provide idtentry_enter/exit()" patch. I'll go read that tomorrow. Thanks! - Joel
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