From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752175AbbGNX00 (ORCPT ); Tue, 14 Jul 2015 19:26:26 -0400 Received: from mail-wg0-f45.google.com ([74.125.82.45]:33254 "EHLO mail-wg0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751241AbbGNX0Z (ORCPT ); Tue, 14 Jul 2015 19:26:25 -0400 Date: Wed, 15 Jul 2015 01:26:21 +0200 From: Frederic Weisbecker To: luto@kernel.org, mingo@kernel.org, luto@amacapital.net, keescook@chromium.org, torvalds@linux-foundation.org, peterz@infradead.org, paulmck@linux.vnet.ibm.com, oleg@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org, vda.linux@googlemail.com, riel@redhat.com, bp@alien8.de, tglx@linutronix.de, dvlasenk@redhat.com, brgerst@gmail.com Cc: linux-tip-commits@vger.kernel.org Subject: Re: [tip:x86/asm] x86/irq, context_tracking: Document how IRQ context tracking works and add an RCU assertion Message-ID: <20150714232620.GE29441@lerouge> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 07, 2015 at 03:54:32AM -0700, tip-bot for Andy Lutomirski wrote: > Commit-ID: 0333a209cbf600e980fc55c24878a56f25f48b65 > Gitweb: http://git.kernel.org/tip/0333a209cbf600e980fc55c24878a56f25f48b65 > Author: Andy Lutomirski > AuthorDate: Fri, 3 Jul 2015 12:44:34 -0700 > Committer: Ingo Molnar > CommitDate: Tue, 7 Jul 2015 10:59:10 +0200 > > x86/irq, context_tracking: Document how IRQ context tracking works and add an RCU assertion > > Signed-off-by: Andy Lutomirski > Cc: Andy Lutomirski > Cc: Borislav Petkov > Cc: Brian Gerst > Cc: Denys Vlasenko > Cc: Denys Vlasenko > Cc: Frederic Weisbecker > Cc: H. Peter Anvin > Cc: Kees Cook > Cc: Linus Torvalds > Cc: Oleg Nesterov > Cc: Paul E. McKenney > Cc: Peter Zijlstra > Cc: Rik van Riel > Cc: Thomas Gleixner > Cc: paulmck@linux.vnet.ibm.com > Link: http://lkml.kernel.org/r/e8bdc4ed0193fb2fd130f3d6b7b8023e2ec1ab62.1435952415.git.luto@kernel.org > Signed-off-by: Ingo Molnar > --- > arch/x86/kernel/irq.c | 15 +++++++++++++++ > 1 file changed, 15 insertions(+) > > diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c > index 88b36648..6233de0 100644 > --- a/arch/x86/kernel/irq.c > +++ b/arch/x86/kernel/irq.c > @@ -216,8 +216,23 @@ __visible unsigned int __irq_entry do_IRQ(struct pt_regs *regs) > unsigned vector = ~regs->orig_ax; > unsigned irq; > > + /* > + * NB: Unlike exception entries, IRQ entries do not reliably > + * handle context tracking in the low-level entry code. This is > + * because syscall entries execute briefly with IRQs on before > + * updating context tracking state, so we can take an IRQ from > + * kernel mode with CONTEXT_USER. The low-level entry code only > + * updates the context if we came from user mode, so we won't > + * switch to CONTEXT_KERNEL. We'll fix that once the syscall > + * code is cleaned up enough that we can cleanly defer enabling > + * IRQs. > + */ > + Now is it a problem to take interrupts in kernel mode with CONTEXT_USER? I'm not sure it's worth trying to make it not happen. > entering_irq(); > > + /* entering_irq() tells RCU that we're not quiescent. Check it. */ > + rcu_lockdep_assert(rcu_is_watching(), "IRQ failed to wake up RCU"); Why do we need to check that? > + > irq = __this_cpu_read(vector_irq[vector]); > > if (!handle_irq(irq, regs)) { Thanks.