Message-ID: <20221005171132.GA519999@roeck-us.net>
Date:   Wed, 5 Oct 2022 10:11:32 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Thorsten Leemhuis <regressions@...mhuis.info>,
        Fenghua Yu <fenghua.yu@...el.com>,
        intel-gfx@...ts.freedesktop.org,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
        regressions@...ts.linux.dev,
        Janusz Krzysztofik <janusz.krzysztofik@...ux.intel.com>,
        Lucas De Marchi <lucas.demarchi@...el.com>,
        linux-hwmon@...r.kernel.org
Subject: Re: [core-for-CI][PATCH] iommu: Remove iova cpu hotplugging flushing

On Wed, Oct 05, 2022 at 05:15:49PM +0100, Robin Murphy wrote:
> On 2022-10-05 16:25, Guenter Roeck wrote:
> > On Wed, Oct 05, 2022 at 04:26:28PM +0200, Thorsten Leemhuis wrote:
> > > [adding the coretemp maintainer (Fenghua Yu) and the appropriate mailing
> > > list to the list of recipients, as there apparently is a coretemp bug
> > > that results in a iommu change causing a regression]
> > > 
> > > On 30.09.22 18:57, Janusz Krzysztofik wrote:
> > > > I think this issue can hit any user with a platform that loads iommu and
> > > > coretemp drivers.  Adding regressions@...ts.linux.dev to the loop.
> > > 
> > > f598a497bc7d was merged for 5.13-rc1, which is quite a while ago, so at
> > > least a quick revert is out of question as it might do more harm than
> > > good. The authors of the commit are kinda responsible for fixing
> > > situations like this; but well, did anybody ask the developers of the
> > > coretemp driver kindly if they are aware of the problem and maybe even
> > > willing to fix it? Doesn't look like it from here from search lore (hope
> > > I didn't miss anything), so let's give it a try.
> > > 
> > > Ciao, Thorsten
> > > 
> > > > On Thursday, 22 September 2022 14:09:35 CEST Robin Murphy wrote:
> > > > > On 22/09/2022 11:10 am, Janusz Krzysztofik wrote:
> > > > > > From: Chris Wilson <chris@...is-wilson.co.uk>
> > > > > > 
> > > > > > Manual revert of commit f598a497bc7d ("iova: Add CPU hotplug handler to
> > > > > > flush rcaches").  It is trying to instantiate a cpuhp notifier from inside
> > > > > > a cpuhp callback.  That code replaced intel_iommu implementation of
> > > > > > flushing per-IOVA domain CPU rcaches which used a single instance of cpuhp
> > > > > > held for the module lifetime.
> > > > > 
> > > > > OK, *now* I see what's going on. It doesn't seem unreasonable to me for
> > > > > bus notifiers to touch CPU hotplug - what seems more unexpected is the
> > > > > coretemp driver creating and adding a platform device from inside a
> > > > > hotplug callback.
> > 
> > It is only unexpected if it is documented that creating a platform driver
> > from a hotplug callback is off limits.
> > 
> > > > > 
> > > > > Once we start trying to revert multiple unrelated bits of important
> > > > > functionality from other subsystems because one driver is doing a weird
> > > > > thing, maybe it's time to instead question whether that driver should be
> > > > > doing a weird thing?
> > 
> > That isn't the point. This _used_ to work, after all. Maybe the functionality
> > introduced with f598a497bc7d is important, but there is still a regression
> > introduced by f598a497bc7d. Sure, maybe the coretemp driver is doing
> > "a weird thing", but if some generic code is changed causing something to fail
> > that previously worked, it is still a regression and the reponsibility of the
> > person or team making the generic code change to fix the problems caused by
> > that change.
> 
> Note that AFAICS I don't think anything's actually broken, and this is
> merely a lockdep false-positive. The coretemp device itself will not be
> associated with the IOMMU, so the IOMMU notifier will never get as far as
> taking any further locks in that particular instance.
> 
> Of course I *can* try writing the patch to fix things properly if I have to,
> but fair warning; I'm not familiar with this driver or the relevant hardware
> or the subsystem, and from a brief look it will involve some significant
> redesign that I have every chance of getting wrong. Plus I'm not sure I can
> test the hotplug stuff at all since the x86 box I have to hand only seems to
> have a single coretemp device.
> 
> The fact is, the wacky thing it's doing with platform_device_add() doesn't
> actually work *all* that well anyway:
> 

Hah, yes, that is obviously a bug. Unfortunately I don't have any systems
with Intel CPU left, so I can not test myself. FWIW, on v5.18.x (which is
what Google laptops use for whatever reason), I don't see the crash, but
"modprobe -r coretemp" followed by "modprobe coretemp" doesn't work -
the driver loads, but does not register with the hwmon subsystem.
There has been no relevant change to the driver since v5.13, so all
I can conclude at this point is that the driver is very likely still
broken in the mainline kernel.

Guenter

> $ sudo rmmod coretemp
> $ echo 0 | sudo tee /sys/bus/platform/drivers_autoprobe
> 0
> $ sudo modprobe coretemp
> 
> [7169271.187103] BUG: kernel NULL pointer dereference, address:
> 0000000000000418
> [7169271.187127] #PF: supervisor write access in kernel mode
> [7169271.187131] #PF: error_code(0x0002) - not-present page
> [7169271.187134] PGD 0 P4D 0
> [7169271.187139] Oops: 0002 [#1] SMP PTI
> [7169271.187144] CPU: 0 PID: 16 Comm: cpuhp/0 Not tainted 5.13.0-52-generic
> #59~20.04.1-Ubuntu
> [7169271.187150] Hardware name: LENOVO 30B6S08J03/1030, BIOS S01KT29A
> 06/20/2016
> [7169271.187152] RIP: 0010:create_core_data+0x3cb/0x510 [coretemp]
> [7169271.187163] Code: 44 89 e7 e8 67 99 7f c8 85 c0 75 17 0f b6 45 b9 41 83
> 46 24 01 69 c0 18 fc ff ff 41 03 46 08 41 89 46 04 48 8b 45 b0 4c 63 fb <4e>
> 89 b4 f8 10 04 00 00 48 8b 00 41 8b 56 24 48 89 45 a0 85 d2 7e
> [7169271.187167] RSP: 0018:ffffa5ddc015fd98 EFLAGS: 00010203
> [7169271.187172] RAX: 0000000000000000 RBX: 0000000000000001 RCX:
> 0000000000000002
> [7169271.187175] RDX: 0000000000000000 RSI: ffffffff89207b30 RDI:
> ffffa5ddc015fd40
> [7169271.187178] RBP: ffffa5ddc015fe00 R08: 0000000000000000 R09:
> ffff8e049c04c800
> [7169271.187181] R10: 0000000000019460 R11: 0000000000000000 R12:
> 0000000000000000
> [7169271.187184] R13: 000000000000005f R14: ffff8e049c04c800 R15:
> 0000000000000001
> [7169271.187187] FS:  0000000000000000(0000) GS:ffff8e0b5f600000(0000)
> knlGS:0000000000000000
> [7169271.187191] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [7169271.187194] CR2: 0000000000000418 CR3: 0000000190672002 CR4:
> 00000000003706f0
> [7169271.187198] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
> 0000000000000000
> [7169271.187200] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
> 0000000000000400
> [7169271.187203] Call Trace:
> [7169271.187206]  <TASK>
> [7169271.187212]  coretemp_cpu_online+0x14f/0x180 [coretemp]
> [7169271.187220]  ? create_core_data+0x510/0x510 [coretemp]
> [7169271.187226]  cpuhp_invoke_callback+0x10b/0x430
> [7169271.187237]  cpuhp_thread_fun+0x92/0x150
> [7169271.187244]  smpboot_thread_fn+0xd0/0x170
> [7169271.187253]  ? sort_range+0x30/0x30
> [7169271.187260]  kthread+0x12b/0x150
> [7169271.187264]  ? set_kthread_struct+0x40/0x40
> [7169271.187269]  ret_from_fork+0x22/0x30
> [7169271.187280]  </TASK>
> 
> Consider that a bug report, unless of course it's documented somewhere that
> users aren't allowed to turn off autoprobe ;)
> 
> Thanks,
> Robin.

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