linux-kernel - Re: [PATCH v1] ACPI / scan: Acquire device_hotplug_lock in acpi_scan

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Message-ID: <ad2d85a0-e7a5-1d76-3984-fa4972853496@redhat.com>
Date:   Thu, 25 Jul 2019 11:23:35 +0200
From:   David Hildenbrand <david@...hat.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Oscar Salvador <osalvador@...e.de>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH v1] ACPI / scan: Acquire device_hotplug_lock in
 acpi_scan_init()

On 25.07.19 11:22, Rafael J. Wysocki wrote:
> On Thu, Jul 25, 2019 at 11:18 AM Oscar Salvador <osalvador@...e.de> wrote:
>>
>> On Wed, Jul 24, 2019 at 04:30:17PM +0200, David Hildenbrand wrote:
>>> We end up calling __add_memory() without the device hotplug lock held.
>>> (I used a local patch to assert in __add_memory() that the
>>>  device_hotplug_lock is held - I might upstream that as well soon)
>>>
>>> [   26.771684]        create_memory_block_devices+0xa4/0x140
>>> [   26.772952]        add_memory_resource+0xde/0x200
>>> [   26.773987]        __add_memory+0x6e/0xa0
>>> [   26.775161]        acpi_memory_device_add+0x149/0x2b0
>>> [   26.776263]        acpi_bus_attach+0xf1/0x1f0
>>> [   26.777247]        acpi_bus_attach+0x66/0x1f0
>>> [   26.778268]        acpi_bus_attach+0x66/0x1f0
>>> [   26.779073]        acpi_bus_attach+0x66/0x1f0
>>> [   26.780143]        acpi_bus_scan+0x3e/0x90
>>> [   26.780844]        acpi_scan_init+0x109/0x257
>>> [   26.781638]        acpi_init+0x2ab/0x30d
>>> [   26.782248]        do_one_initcall+0x58/0x2cf
>>> [   26.783181]        kernel_init_freeable+0x1bd/0x247
>>> [   26.784345]        kernel_init+0x5/0xf1
>>> [   26.785314]        ret_from_fork+0x3a/0x50
>>>
>>> So perform the locking just like in acpi_device_hotplug().
>>>
>>> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
>>> Cc: Len Brown <lenb@...nel.org
>>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>>> Cc: Oscar Salvador <osalvador@...e.de>
>>> Cc: Michal Hocko <mhocko@...e.com>
>>> Signed-off-by: David Hildenbrand <david@...hat.com>
>>
>> Given that that call comes from a __init function, so while booting, I wonder
>> how bad it is.
> 
> Yes, it probably does not matter.

It can at least confuse lockdep, but I agree that this is not stable
material.

> 
>> Anyway, let us be consistent:
> 
> Right.
> 


-- 

Thanks,

David / dhildenb