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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Tue, 4 Jun 2019 09:36:29 +0100 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp23032.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x548aS8h19726796 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 4 Jun 2019 08:36:28 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id BF2E7B2068; Tue, 4 Jun 2019 08:36:28 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 6D1C9B206A; Tue, 4 Jun 2019 08:36:28 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.85.171.86]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Tue, 4 Jun 2019 08:36:28 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id D2BED16C5D9E; Tue, 4 Jun 2019 00:45:49 -0700 (PDT) Date: Tue, 4 Jun 2019 00:45:49 -0700 From: "Paul E. McKenney" To: Dietmar Eggemann Cc: Mark Rutland , Peter Zijlstra , tglx@linutronix.de, mingo@kernel.org, jpoimboe@redhat.com, mojha@codeaurora.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH HACK RFC] cpu: Prevent late-arriving interrupts from disrupting offline Reply-To: paulmck@linux.ibm.com References: <20190602011253.GA6167@linux.ibm.com> <20190603083848.GB3436@hirez.programming.kicks-ass.net> <20190603114455.GA16119@lakrids.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 19060408-0040-0000-0000-000004F85F29 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00011212; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000286; SDB=6.01213024; UDB=6.00637520; IPR=6.00994092; MB=3.00027177; MTD=3.00000008; XFM=3.00000015; UTC=2019-06-04 08:36:32 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19060408-0041-0000-0000-000009047D28 Message-Id: <20190604074549.GP28207@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-06-04_07:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1906040058 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 03, 2019 at 03:39:18PM +0200, Dietmar Eggemann wrote: > On 6/3/19 1:44 PM, Mark Rutland wrote: > >On Mon, Jun 03, 2019 at 10:38:48AM +0200, Peter Zijlstra wrote: > >>On Sat, Jun 01, 2019 at 06:12:53PM -0700, Paul E. McKenney wrote: > >>>Scheduling-clock interrupts can arrive late in the CPU-offline process, > >>>after idle entry and the subsequent call to cpuhp_report_idle_dead(). > >>>Once execution passes the call to rcu_report_dead(), RCU is ignoring > >>>the CPU, which results in lockdep complaints when the interrupt handler > >>>uses RCU: > >> > >>>diff --git a/kernel/cpu.c b/kernel/cpu.c > >>>index 448efc06bb2d..3b33d83b793d 100644 > >>>--- a/kernel/cpu.c > >>>+++ b/kernel/cpu.c > >>>@@ -930,6 +930,7 @@ void cpuhp_report_idle_dead(void) > >>> struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state); > >>> BUG_ON(st->state != CPUHP_AP_OFFLINE); > >>>+ local_irq_disable(); > >>> rcu_report_dead(smp_processor_id()); > >>> st->state = CPUHP_AP_IDLE_DEAD; > >>> udelay(1000); > >> > >>Urgh... I'd almost suggest we do something like the below. > >> > >> > >>But then I started looking at the various arch_cpu_idle_dead() > >>implementations and ran into arm's implementation, which is calling > >>complete() where generic code already established this isn't possible > >>(see for example cpuhp_report_idle_dead()). > > > >IIRC, that should have been migrated over to cpu_report_death(), as > >arm64 was in commit: > > > > 05981277a4de1ad6 ("arm64: Use common outgoing-CPU-notification code") > > > >... but it looks like Paul's patch to do so [1] fell through the cracks; > >I'm not aware of any reason that shouldn't have been taken. > >[1] https://lore.kernel.org/lkml/1431467407-1223-8-git-send-email-paulmck@linux.vnet.ibm.com/ > > > >Paul, do you want to resend that? > > Please do. We're carrying this patch out-of-tree for while now in > our EAS integration to get cpu hotplug tests passing on TC2 (arm). Huh. It still applies. But I have no means of testing it. And it looks like the reason I dropped it was that I didn't get any response from the maintainer. I sent a message to this effect to linux-arm-kernel@lists.infradead.org and linux@arm.linux.org.uk on May 21, 2015. So here it is again. ;-) I have queued this locally. Left to myself, I add the two of you on its Cc: list and run it through my normal process. But given the history, I would still want either an ack from the maintainer or, better, for the maintainer to take the patch. Or is there a better way for us to proceed on this? Thanx, Paul ------------------------------------------------------------------------ arm: Use common outgoing-CPU-notification code This commit removes the open-coded CPU-offline notification with new common code. In particular, this change avoids calling scheduler code using RCU from an offline CPU that RCU is ignoring. This is a minimal change. A more intrusive change might invoke the cpu_check_up_prepare() and cpu_set_state_online() functions at CPU-online time, which would allow onlining throw an error if the CPU did not go offline properly. Signed-off-by: Paul E. McKenney Cc: linux-arm-kernel@lists.infradead.org Cc: Russell King diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c index ebc53804d57b..8687d619260f 100644 --- a/arch/arm/kernel/smp.c +++ b/arch/arm/kernel/smp.c @@ -267,15 +267,13 @@ int __cpu_disable(void) return 0; } -static DECLARE_COMPLETION(cpu_died); - /* * called on the thread which is asking for a CPU to be shutdown - * waits until shutdown has completed, or it is timed out. */ void __cpu_die(unsigned int cpu) { - if (!wait_for_completion_timeout(&cpu_died, msecs_to_jiffies(5000))) { + if (!cpu_wait_death(cpu, 5)) { pr_err("CPU%u: cpu didn't die\n", cpu); return; } @@ -322,7 +320,7 @@ void arch_cpu_idle_dead(void) * this returns, power and/or clocks can be removed at any point * from this CPU and its cache by platform_cpu_kill(). */ - complete(&cpu_died); + (void)cpu_report_death(); /* * Ensure that the cache lines associated with that completion are