Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933878AbdCVJyZ (ORCPT ); Wed, 22 Mar 2017 05:54:25 -0400 Received: from mail2-relais-roc.national.inria.fr ([192.134.164.83]:58240 "EHLO mail2-relais-roc.national.inria.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932606AbdCVJyV (ORCPT ); Wed, 22 Mar 2017 05:54:21 -0400 X-IronPort-AV: E=Sophos;i="5.36,204,1486422000"; d="scan'208";a="265646057" Date: Wed, 22 Mar 2017 10:54:15 +0100 (CET) From: Julia Lawall X-X-Sender: jll@hadrien To: Julia Cartwright cc: Julia Lawall , Gilles Muller , Nicolas Palix , Michal Marek , linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org, Thomas Gleixner , Sebastian Andrzej Siewior , Linus Walleij , cocci@systeme.lip6.fr Subject: Re: [PATCH v2 1/9] Coccinelle: locks: identify callers of spin_lock{,_irq,_irqsave}() in irqchip implementations In-Reply-To: <48a11ad61edb4bec130f2ae0d46fc4e7d4855044.1490135047.git.julia@ni.com> Message-ID: References: <48a11ad61edb4bec130f2ae0d46fc4e7d4855044.1490135047.git.julia@ni.com> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4068 Lines: 147 On Tue, 21 Mar 2017, Julia Cartwright wrote: > On PREEMPT_RT, the spinlock_t type becomes an object which sleeps under > contention. The codepaths used to support scheduling (irq dispatching, arch > code, the scheduler, timers) therefore must make use of the > raw_spin_lock{,_irq,_irqsave}() variations which preserve the non-sleeping > spinlock behavior. > > Because the irq_chip callbacks are invoked in the process of interrupt > dispatch, they cannot therefore make use of spin_lock_t type. Instead, the > usage of raw_spinlock_t is appropriate. > > Provide a spatch to identify (and attempt to patch) such problematic irqchip > implementations. > > Note to those generating patches using this spatch; in order to maintain > correct semantics w/ PREEMPT_RT, it is necessary to audit the > raw_spinlock_t-protected codepaths to ensure their execution is bounded and > minimal. This is a manual audit process. > > See commit 47b03ca903fb0 ("pinctrl: qcom: Use raw spinlock variants") as an > example of _one_ such instance, which fixed a real bug seen in the field. > > Cc: Thomas Gleixner > Cc: Sebastian Andrzej Siewior > Cc: Linus Walleij > Signed-off-by: Julia Cartwright Acked-by: Julia Lawall > --- > v1 -> v2: > - Make use of 'exists' on match to find any codepath which acquires a lock. (via Julia Lawall) > - Use 'when any' on '...' matches to loosen constraint (via Julia Lawall). > > .../coccinelle/locks/irq_chip_raw_spinlock.cocci | 96 ++++++++++++++++++++++ > 1 file changed, 96 insertions(+) > create mode 100644 scripts/coccinelle/locks/irq_chip_raw_spinlock.cocci > > diff --git a/scripts/coccinelle/locks/irq_chip_raw_spinlock.cocci b/scripts/coccinelle/locks/irq_chip_raw_spinlock.cocci > new file mode 100644 > index 000000000000..0294831297d3 > --- /dev/null > +++ b/scripts/coccinelle/locks/irq_chip_raw_spinlock.cocci > @@ -0,0 +1,96 @@ > +// Copyright: (C) 2017 National Instruments Corp. GPLv2. > +// Author: Julia Cartwright > +// > +// Identify callers of non-raw spinlock_t functions in hardirq irq_chip > +// callbacks. > +// > +// spin_lock{_irq,_irqsave}(), w/ PREEMPT_RT are "sleeping" spinlocks, and so > +// therefore "sleep" under contention; identify (and potentially patch) callers > +// to use raw_spinlock_t instead. > +// > +// Confidence: Moderate > + > +virtual report > +virtual patch > + > +@match@ > +identifier __irqchip; > +identifier __irq_mask; > +@@ > + static struct irq_chip __irqchip = { > + .irq_mask = __irq_mask, > + }; > + > +@match2 depends on match exists@ > +identifier match.__irq_mask; > +identifier data; > +identifier x; > +identifier l; > +type T; > +position j0; > +expression flags; > +@@ > + static void __irq_mask(struct irq_data *data) > + { > + ... when any > + T *x; > + ... when any > +( > + spin_lock_irqsave(&x->l@j0, flags); > +| > + spin_lock_irq(&x->l@j0); > +| > + spin_lock(&x->l@j0); > +) > + ... when any > + } > + > +@match3 depends on match2 && patch@ > +type match2.T; > +identifier match2.l; > +@@ > + T { > + ... > +- spinlock_t l; > ++ raw_spinlock_t l; > + ... > + }; > + > +@match4 depends on match2 && patch@ > +type match2.T; > +identifier match2.l; > +expression flags; > +T *x; > +@@ > + > +( > +-spin_lock(&x->l) > ++raw_spin_lock(&x->l) > +| > +-spin_lock_irqsave(&x->l, flags) > ++raw_spin_lock_irqsave(&x->l, flags) > +| > +-spin_lock_irq(&x->l) > ++raw_spin_lock_irq(&x->l) > +| > +-spin_unlock(&x->l) > ++raw_spin_unlock(&x->l) > +| > +-spin_unlock_irq(&x->l) > ++raw_spin_unlock_irq(&x->l) > +| > +-spin_unlock_irqrestore(&x->l, flags) > ++raw_spin_unlock_irqrestore(&x->l, flags) > +| > +-spin_lock_init(&x->l) > ++raw_spin_lock_init(&x->l) > +) > + > +@script:python wat depends on match2 && report@ > +j0 << match2.j0; > +t << match2.T; > +l << match2.l; > +@@ > + > +msg = "Use of non-raw spinlock is illegal in this context (%s::%s)" % (t, l) > +coccilib.report.print_report(j0[0], msg) > -- > 2.12.0 > >