Date: Mon, 11 Dec 2017 14:20:17 -0600
From: Julia Cartwright <julia@ni.com>
To: Corey Minyard <cminyard@mvista.com>
CC: LKML <linux-kernel@vger.kernel.org>,
        linux-rt-users <linux-rt-users@vger.kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>, Carsten Emde <C.Emde@osadl.org>,
        John Kacur <jkacur@redhat.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Daniel Wagner <daniel.wagner@siemens.com>,
        <tom.zanussi@linux.intel.com>, Alex Shi <alex.shi@linaro.org>
Subject: Re: [ANNOUNCE] 4.1.46-rt52
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On Mon, Dec 11, 2017 at 01:04:58PM -0600, Corey Minyard wrote:
> On 11/29/2017 05:13 PM, Julia Cartwright wrote:
> > Hello RT Folks!
> > 
> > I'm pleased to announce the 4.1.46-rt52 stable release.
> > 
> > You can get this release via the git tree at:
> > 
> >    git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-stable-rt.git
> > 
> >    branch: v4.1-rt
> >    Head SHA1: 6e737a91c1ce923d4e10db831e14cfef9a2459cc
> > 
> > Or to build 4.1.46-rt52 directly, the following patches should be applied:
> > 
> >    https://urldefense.proofpoint.com/v2/url?u=http-3A__www.kernel.org_pub_linux_kernel_v4.x_linux-2D4.1.tar.xz&d=DwICaQ&c=I_0YwoKy7z5LMTVdyO6YCiE2uzI1jjZZuIPelcSjixA&r=cAXq_8W9Othb2h8ZcWv8Vw&m=a5KTpX9A0-pHwmQkOOLr5_xeWPavI-lgN7Z0Goes2So&s=tGmSNpZKEKvhTpeVu_ktmD4I5PIXfIJhZ79DxwbCjtQ&e=
> > 
> >    https://urldefense.proofpoint.com/v2/url?u=http-3A__www.kernel.org_pub_linux_kernel_v4.x_patch-2D4.1.46.xz&d=DwICaQ&c=I_0YwoKy7z5LMTVdyO6YCiE2uzI1jjZZuIPelcSjixA&r=cAXq_8W9Othb2h8ZcWv8Vw&m=a5KTpX9A0-pHwmQkOOLr5_xeWPavI-lgN7Z0Goes2So&s=hx9pHgRy7tWhUeeiJhPOH0T8qdDrhtZvWxOWuIBZZgs&e=
> > 
> >    https://urldefense.proofpoint.com/v2/url?u=http-3A__www.kernel.org_pub_linux_kernel_projects_rt_4.1_patch-2D4.1.46-2Drt52.patch.xz&d=DwICaQ&c=I_0YwoKy7z5LMTVdyO6YCiE2uzI1jjZZuIPelcSjixA&r=cAXq_8W9Othb2h8ZcWv8Vw&m=a5KTpX9A0-pHwmQkOOLr5_xeWPavI-lgN7Z0Goes2So&s=Pm8ed_xvW1drpPxNkt035bj6ILvSImuN9vvgEAt8IiM&e=
> > 
> > 
> > You can also build from 4.1.46-rt51 by applying the incremental patch:
> > 
> >    https://urldefense.proofpoint.com/v2/url?u=http-3A__www.kernel.org_pub_linux_kernel_projects_rt_4.1_incr_patch-2D4.1.46-2Drt51-2Drt52.patch.xz&d=DwICaQ&c=I_0YwoKy7z5LMTVdyO6YCiE2uzI1jjZZuIPelcSjixA&r=cAXq_8W9Othb2h8ZcWv8Vw&m=a5KTpX9A0-pHwmQkOOLr5_xeWPavI-lgN7Z0Goes2So&s=ZM64-JCd0WNFQgFlB3wbCfn8Jtf9rq5QyCO2-GJsC2Q&e=
> > 
> > Enjoy!
> >     Julia
> > 
> > Changes from v4.1.46-rt51:
> > ---
> > Julia Cartwright (2):
> >        workqueue: fixup rcu check for RT
> >        Linux 4.1.46-rt52
> > 
> > Sebastian Andrzej Siewior (2):
> >        PM / CPU: replace raw_notifier with atomic_notifier (fixup)
> 
> This change breaks the compile of 4.1 on ARM (and other things using
> kernel/cpu_pm.c).
> 
> rcu_irq_enter_irqson() and friends doesn't exist in 4.1.  In fact,
> rcu_irq_enter() doesn't even exist.
> 
> Sorry I didn't get to testing this earlier, I've been focused on other things.

Thanks!  My current builds apparently don't currently cover CPU_PM
builds, so I didn't see this :(.  Thanks for the report.

v4.1 does contain rcu_irq_enter(), and it looks like what we should be
using in 4.1 instead.

I'm thinking the below should be okay; I'll be standing up a proper cpu
hotplugging test to give it some runtime.

Thanks,
   Julia

-- 8< --
Subject: [PATCH] PM / CPU: replace usage of rcu_irq_{enter,exit}_irqson()

Commit c50243950f97e ("PM / CPU: replace raw_notifier with
atomic_notifier (fixup)") intended to fix up RCU usage in idle, by
telling RCU to pay attention.

However, the cherry-pick back from rt-devel included the invocation of
the _irqson() variants of rcu_irq_{enter,exit}() API which doesn't exist
in 4.1.

For 4.1, just simply drop the _irqson() variant, and instead use
rcu_irq_{enter,exit}() directly instead.  This is safe, because in 4.1,
these functions internally disable interrupts.

Reported-by: Corey Minyard <cminyard@mvista.com>
Signed-off-by: Julia Cartwright <julia@ni.com
---
 kernel/cpu_pm.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/cpu_pm.c b/kernel/cpu_pm.c
index d1d1c3961553..eeff3c382793 100644
--- a/kernel/cpu_pm.c
+++ b/kernel/cpu_pm.c
@@ -33,10 +33,10 @@ static int cpu_pm_notify(enum cpu_pm_event event, int nr_to_call, int *nr_calls)
 	 * could be disfunctional in cpu idle. Copy RCU_NONIDLE code to let
 	 * RCU know this.
 	 */
-	rcu_irq_enter_irqson();
+	rcu_irq_enter();
 	ret = __atomic_notifier_call_chain(&cpu_pm_notifier_chain, event, NULL,
 		nr_to_call, nr_calls);
-	rcu_irq_exit_irqson();
+	rcu_irq_exit();
 
 	return notifier_to_errno(ret);
 }
-- 
2.14.2