From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758054AbdJKUsf (ORCPT ); Wed, 11 Oct 2017 16:48:35 -0400 Received: from mailgw1.fjfi.cvut.cz ([147.32.9.3]:35614 "EHLO mailgw1.fjfi.cvut.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751386AbdJKUsc (ORCPT ); Wed, 11 Oct 2017 16:48:32 -0400 X-CTU-FNSPE-Virus-Scanned: amavisd-new at fjfi.cvut.cz DKIM-Filter: OpenDKIM Filter v2.11.0 mailgw1.fjfi.cvut.cz D6607A029C Date: Wed, 11 Oct 2017 22:48:26 +0200 (CEST) From: David Kozub To: Daniel Lezcano cc: Thomas Gleixner , linux-kernel@vger.kernel.org Subject: Re: PROBLEM: Kernel BUG in mfgpt_tick (cs5535-clockevt.c) on ALIX 2c3 - null call In-Reply-To: Message-ID: References: <8de07c60-8d37-802a-837c-a6cf356d1535@linaro.org> <29c0b5e6-3285-a307-4045-6b2b9f9747d6@linaro.org> User-Agent: Alpine 2.21 (LRH 202 2017-01-01) MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="546533125-135119199-1507754906=:21191" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --546533125-135119199-1507754906=:21191 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8BIT On Wed, 11 Oct 2017, Daniel Lezcano wrote: > On 10/10/2017 23:19, David Kozub wrote: >> On Tue, 10 Oct 2017, Daniel Lezcano wrote: >> >>> On 09/10/2017 21:33, David Kozub wrote: >>>> On Mon, 9 Oct 2017, Daniel Lezcano wrote: >>>> >>>>> On 07/10/2017 23:26, David Kozub wrote: >>>>>> Hi all, >>>>>> >>>>>> booting up kernel 4.14-rc3 with CS5535_CLOCK_EVENT_SRC on an ALIX 2c3 >>>>>> (http://pcengines.ch/alix2c3.htm) dies with: >>>>>> >>>>>> [    2.313086] cs5535-smb cs5535-smb: SCx200 device 'CS5535 ACB0' >>>>>> registered >>>>>> [    2.338711] cs5535-mfgpt cs5535-mfgpt: registered timer 0 >>>>>> [    2.355676] ledtrig-cpu: registered to indicate activity on CPUs >>>>>> [    2.373745] cs5535-mfgpt cs5535-mfgpt: registered timer 1 >>>>>> [    2.389976] cs5535-clockevt: Registering MFGPT timer as a clock >>>>>> event, using IRQ 7 >>>>>> [    2.412687] BUG: unable to handle kernel NULL pointer dereference >>>>>> at   (null) >>>>>> [    2.412698] IP:   (null) >>>>>> [    2.412702] *pde = 00000000 >>>>>> [    2.412713] Oops: 0000 [#1] >>>>>> [    2.412716] Modules linked in: >>>>>> [    2.412732] CPU: 0 PID: 1 Comm: swapper Not tainted >>>>>> 4.14.0-rc3-humel-test17 #36 >>>>>> [    2.412739] task: c0010000 task.stack: c008e000 >>>>>> [    2.412744] EIP:   (null) >>>>>> [    2.412749] EFLAGS: 00210093 CPU: 0 >>>>>> [    2.412758] EAX: c05fb8c0 EBX: c05fb880 ECX: 00000000 EDX: 0000620c >>>>>> [    2.412769] ESI: c0009fd4 EDI: c014e14e EBP: c0009fac ESP: c0009fa8 >>>>>> [    2.412780]  DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 0068 >>>>>> [    2.412790] CR0: 80050033 CR2: 00000000 CR3: 0064f000 CR4: 00000090 >>>>>> [    2.412793] Call Trace: >>>>>> [    2.412800]  >>>>>> [    2.412825]  ? mfgpt_tick+0x5d/0x81 >>>>>> [    2.412845]  __handle_irq_event_percpu+0x56/0xb6 >>>>>> [    2.412864]  ? handle_fasteoi_irq+0xf3/0xf3 >>>>>> [    2.412878]  handle_irq_event_percpu+0x17/0x3f >>>>>> [    2.412892]  handle_irq_event+0x1d/0x29 >>>>>> [    2.412905]  handle_level_irq+0x57/0xc6 >>>>>> [    2.412924]  handle_irq+0x47/0x52 >>>>>> [    2.412929]  >>>>>> [    2.412934]  >>>>>> [    2.412949]  do_IRQ+0x32/0x9b >>>>>> [    2.412963]  ? __irqentry_text_end+0x7/0x7 >>>>>> [    2.412976]  common_interrupt+0x2e/0x34 >>>>>> ... >>>>>> >>>>>> The problem seems to be in drivers/clocksource/cs5535-clockevt.c in >>>>>> mfgpt_tick() on line 132: >>>>>> ... >>>>>>     cs5535_clockevent.event_handler(&cs5535_clockevent); >>>>>> ... >>>>>> cs5535_clockevent.event_handler is null. >>>>>> >>>>>> Adding some more traces I see mfgpt_tick() gets called before >>>>>> clockevents_config_and_register() finishes (invoked from >>>>>> cs5535_mfgpt_init() on line 178). So when mfgpt_tick() accessess the >>>>>> event_handler, it's NULL. Wrapping the event_handler call on line >>>>>> 132 in >>>>>> a null pointer check results in a working system. >>>>>> >>>>>> The issue is present at least also in kernel 4.13.5. In kernel >>>>>> versions >>>>>> <= 4.1-rc6 the cs5535_clockevent worked OK. Kernels >= 4.1-rc7 never >>>>>> booted at all on my ALIX 2c3 (last I tried 4.5, then gave up and tried >>>>>> 4.13.5 recently), so I don't know when exactly this issue appeared. >>>>>> >>>>>> My guess is that the timer interrupt is enabled too early. If I change >>>>>> the order of clockevents_config_and_register() and >>>>>> cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_SETUP, val) in >>>>>> cs5535_mfgpt_init() like this: >>>>>> ... >>>>>>     /* Set up the clock event */ >>>>>>     printk(KERN_INFO DRV_NAME >>>>>>         ": Registering MFGPT timer as a clock event, using IRQ %d\n", >>>>>>         timer_irq); >>>>>>     clockevents_config_and_register(&cs5535_clockevent, MFGPT_HZ, >>>>>>                     0xF, 0xFFFE); >>>>>> >>>>>>     /* Set the clock scale and enable the event mode for CMP2 */ >>>>>>     val = MFGPT_SCALE | (3 << 8); >>>>>>     cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_SETUP, val); >>>>>> ... >>>>>> the system boots and seems to be OK. >>>>> >>>>> What happens if instead of inverting those two lines, you add >>>>> mfgpt_shutdown() early in the init function ? >>>> >>>> Hi Daniel, >>>> >>>> I can't call mfgpt_shutdown() before clockevents_config_and_register() >>>> as mfgpt_shutdown() wants a struct clock_event_device* which is only >>>> available after clockevents_config_and_register(). But I tried calling >>>> disable_timer(): >>>> >>>> @@ -152,6 +152,8 @@ static int __init cs5535_mfgpt_init(void) >>>>         } >>>>         cs5535_event_clock = timer; >>>> >>>> +       disable_timer(cs5535_event_clock); >>>> + >>>>         /* Set up the IRQ on the MFGPT side */ >>>>         if (cs5535_mfgpt_setup_irq(timer, MFGPT_CMP2, &timer_irq)) { >>>>                 printk(KERN_ERR DRV_NAME ": Could not set up IRQ %d\n", >>>> >>>> which should do the same thing. Unfortunately I still get the same BUG. >>>> >>>> I added some more traces and I think the IRQ comes just after: >>>>     ret = setup_irq(timer_irq, &mfgptirq); >>> >>> Mmh, the interrupt flag tells it is a shared interrupt, bad :/ >> >> While there is IRQF_SHARED, I think on the ALIX 2c3 the IRQ is not >> really shared: >> >> $ cat /proc/interrupts >>            CPU0 >>   0:       9959    XT-PIC      timer >>   2:          0    XT-PIC      cascade >>   4:       1763    XT-PIC      ttyS0 >>   7:       4648    XT-PIC      cs5535-clockevt >>   9:          0    XT-PIC      ath >>  10:        151    XT-PIC      eth0 >>  11:          0    XT-PIC      eth1 >>  12:          1    XT-PIC      ehci_hcd:usb1, ohci_hcd:usb2 >>  14:       4063    XT-PIC      pata_cs5536 >>  15:          0    XT-PIC      eth2 >> >> (if this is sufficient proof) > > After digging a bit, the interrupt can be shared. There is a comment in > the drivers/misc/cs5535-mfgpt.c:cs5535_mfgpt_set_irq() function. > > Moreover, the kernel can boot with a module parameter to change the irq > number. By config, the default is 7 but it could be another interrupt > shared with a device. > > But your setup, if I refer the output of /proc/interrupts, does not show > the interrupt timer is shared. > >>> The interrupt handler checks if the interrupt was for the timer. >>> >>> So here, there are two options: >>> >>> - the timer is in an inconsistent state, with an interrupt line up and >>> enabled. In this case, it should be reseted correctly before going >>> further in the init function (disable, ack irq if any, and then request >>> irq and register). >>> >>> .. or .. >>> >>> - the check at the beginning of the interrupt handler: >>>        /* See if the interrupt was for us */ >>>        if (!(val & (MFGPT_SETUP_SETUP | MFGPT_SETUP_CMP2 | >>>         MFGPT_SETUP_CMP1))) >>>                return IRQ_NONE; >>> >>>   does not work and we try to handle an interrupt which is not for us. >> >> If this interrupt is not shared, this option can be ruled out, right? > > Yes. > >>> That could be any of these two (or both) and I suspect the commit >>> 8f9327cbb brings to light this problem as before the interrupt handler >>> had the check: >>>     if (cs5535_tick_mode == CLOCK_EVT_MODE_SHUTDOWN) >>>         return IRQ_HANDLED; >>> >>> with: >>> >>> static unsigned int cs5535_tick_mode = CLOCK_EVT_MODE_SHUTDOWN; >> >> I agree, in the previous version any early calls would be ignored. >> >> I see in http://pcengines.ch/pdf/alix2.pdf on page 10 in "Setup >> options": "M: toggles MFGPT workaround – may be required to support high >> speed timer. See AMD CS5536 data book section 5.16.3 for the gory >> details. The system may hang during boot if you get it wrong…" >> >> I tried toggling the option and it didn't seem to have any effect on >> this issue. Furthermore I did a BIOS update and now the menu option is >> gone. >> >> The CD5536 Data Book is here: >> https://support.amd.com/TechDocs/33238G_cs5536_db.pdf and that 5.16.3 >> issue doesn't seem to be relevant here. >> >> So I think the following must be happening: >> >>> - the timer is in an inconsistent state, with an interrupt line up and >>> enabled. In this case, it should be reseted correctly before going >>> further in the init function (disable, ack irq if any, and then request >>> irq and register). >> >> Should I do something more to verify that it is this case? >> >> Could you please give me more detailed info on how to reset the IRQ to a >> sane sate? Being a kernel noob that summary is not sufficient for me. > > The code should be already there in the driver. > > Usually, in order to prevent this kind issue, before calling > clockevent_config_and_register(), we disable the timer and ack > unconditionally any interrupt. > > So at the first glance, I would add: > > diff --git a/drivers/clocksource/cs5535-clockevt.c > b/drivers/clocksource/cs5535-clockevt.c > index a1df588..87e9581 100644 > --- a/drivers/clocksource/cs5535-clockevt.c > +++ b/drivers/clocksource/cs5535-clockevt.c > @@ -152,6 +152,9 @@ static int __init cs5535_mfgpt_init(void) > } > cs5535_event_clock = timer; > > + disable_timer(timer); > + cs5535_mfgpt_write(timer, MFGPT_REG_COUNTER, 0); > + > /* Set up the IRQ on the MFGPT side */ > if (cs5535_mfgpt_setup_irq(timer, MFGPT_CMP2, &timer_irq)) { > printk(KERN_ERR DRV_NAME ": Could not set up IRQ %d\n", I tried that and the handler is still called. So I did some more random experiments and I found out that if I call disable_timer(timer) twice, then the issue is resolved (the handler is not called before the registration is finished.) And I don't have to set MFGPT_REG_COUNTER to 0. I have no idea why do I have to call disable_timer twice. Best regards, David --546533125-135119199-1507754906=:21191--