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Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gpd7z-0001Ub-QN; Fri, 01 Feb 2019 18:01:23 +0000 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70] helo=foss.arm.com) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gpd7w-0001TL-E5 for linux-arm-kernel@lists.infradead.org; Fri, 01 Feb 2019 18:01:22 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B0E6715BE; Fri, 1 Feb 2019 10:01:18 -0800 (PST) Received: from fuggles.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7D4913F589; Fri, 1 Feb 2019 10:01:17 -0800 (PST) Date: Fri, 1 Feb 2019 18:01:12 +0000 From: Will Deacon To: Robin Murphy Subject: Re: Could you please help to have a look a bug trace in pmu arm-cci.c Message-ID: <20190201180112.GA14755@fuggles.cambridge.arm.com> References: <529F9A9100AE8045A7A5B5A00A39FBB862099B8E@ALA-MBD.corp.ad.wrs.com> <20190130182128.GM18558@fuggles.cambridge.arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.1+86 (6f28e57d73f2) () X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190201_100120_487105_294E6D96 X-CRM114-Status: GOOD ( 25.98 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "mark.rutland@arm.com" , "Li, Meng" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , suzuki.poulose@arm.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Jan 30, 2019 at 07:09:42PM +0000, Robin Murphy wrote: > On 2019-01-30 6:21 pm, Will Deacon wrote: > > [+Suzuki and Robin] > > > > On Mon, Jan 28, 2019 at 07:19:20AM +0000, Li, Meng wrote: > > > When enable kernel configure CONFIG_DEBUG_ATOMIC_SLEEP, there is below trace > > > during pmu arm cci driver probe phase. > > > > > > [ 1.983337] BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:2004 > > > [ 1.983340] in_atomic(): 1, irqs_disabled(): 0, pid: 1, name: swapper/0 > > > [ 1.983342] Preemption disabled at: > > > [ 1.983353] [] cci_pmu_probe+0x1dc/0x488 > > > [ 1.983360] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.18.20-rt8-yocto-preempt-rt #1 > > > [ 1.983362] Hardware name: ZynqMP ZCU102 Rev1.0 (DT) > > > [ 1.983364] Call trace: > > > [ 1.983369] dump_backtrace+0x0/0x158 > > > [ 1.983372] show_stack+0x24/0x30 > > > [ 1.983378] dump_stack+0x80/0xa4 > > > [ 1.983383] ___might_sleep+0x138/0x160 > > > [ 1.983386] __might_sleep+0x58/0x90 > > > [ 1.983391] __rt_mutex_lock_state+0x30/0xc0 > > > [ 1.983395] _mutex_lock+0x24/0x30 > > > [ 1.983400] perf_pmu_register+0x2c/0x388 > > > [ 1.983404] cci_pmu_probe+0x2bc/0x488 > > > [ 1.983409] platform_drv_probe+0x58/0xa8 > > > > > > Because get_cpu() is invoked, preempt is disable, finally, trace occurs when > > > call might_sleep() > > > > Hmm, the {get,put}_cpu() usage here looks very broken to me. There's the > > fact that it might sleep, but also the assignment to g_cci_pmu is done after > > we've re-enabled preemption, so there's a race with CPU hotplug there too. > > Hmm, looks like I failed to appreciate that particular race at the time - > indeed the global should probably be assigned immediately after > cci_pmu_init() has succeeded. > > > I don't think we can simply register the hotplug notifier before registering > > the PMU, because we can't call into perf_pmu_migrate_context() until the PMU > > has been registered. Perhaps we need to use the _cpuslocked() versions of > > the hotplug notifier registration functions. > > > > I tried looking at some other drivers, but they all look broken to me, so > > there's a good chance I'm missing something. Anybody know how this is > > supposed to work? > > As I understand the general pattern, we register the notifier last to avoid > taking a hotplug callback with a partly-initialised PMU state, however since > the CPU we've picked is part of that PMU state, we also want to avoid > getting migrated off that CPU before the notifier is in place lest things > get out of sync, hence disabling preemption. As far as the correctness of > implementing that logic, though, it was like that when I got here so I've > always just assumed it was fine :) > > I guess the question is whether we actually need to pick our nominal CPU > before perf_pmu_register(), or if something like the below would suffice - > what do you reckon? > > Robin. > > ----->8----- > diff --git a/drivers/perf/arm-cci.c b/drivers/perf/arm-cci.c > index 1bfeb160c5b1..da9309ff80d7 100644 > --- a/drivers/perf/arm-cci.c > +++ b/drivers/perf/arm-cci.c > @@ -1692,19 +1692,18 @@ static int cci_pmu_probe(struct platform_device > *pdev) > raw_spin_lock_init(&cci_pmu->hw_events.pmu_lock); > mutex_init(&cci_pmu->reserve_mutex); > atomic_set(&cci_pmu->active_events, 0); > - cci_pmu->cpu = get_cpu(); > + cci_pmu->cpu = -1; /* Avoid races until hotplug notifier is alive */ > > ret = cci_pmu_init(cci_pmu, pdev); So at this point we've registered the PMU with perf, so I think we're open to userspace. Given that things like pmu_cpumask_attr_show() call cpumask_of(cci_pmu->cpu), having a cpu of -1 seems like a bad idea. Why not just use the _cpuslocked() notifier registration functions so that we don't need to disable preemption? Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel