From: David Hildenbrand <david@redhat.com>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux Memory Management List <linux-mm@kvack.org>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
devel@linuxdriverproject.org, linux-s390@vger.kernel.org,
xen-devel@lists.xenproject.org,
Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@suse.com>, Vlastimil Babka <vbabka@suse.cz>,
Dan Williams <dan.j.williams@intel.com>,
Pavel Tatashin <pasha.tatashin@oracle.com>,
osalvador@suse.de, Vitaly Kuznetsov <vkuznets@redhat.com>,
Martin Schwidefsky <schwidefsky@de.ibm.com>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
kys@microsoft.com, haiyangz@microsoft.com,
sthemmin@microsoft.com,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Len Brown <lenb@kernel.org>, David Rientjes <rientjes@google.com>
Subject: Re: [PATCH RFC 1/2] drivers/base: export lock_device_hotplug/unlock_device_hotplug
Date: Fri, 17 Aug 2018 11:41:24 +0200 [thread overview]
Message-ID: <42df9062-f647-3ad6-5a07-be2b99531119@redhat.com> (raw)
In-Reply-To: <CAJZ5v0gkYV8o2Eq+EcGT=OP1tQGPGVVe3n9VGD6z7KAVVqhv9w@mail.gmail.com>
On 17.08.2018 11:03, Rafael J. Wysocki wrote:
> On Fri, Aug 17, 2018 at 10:56 AM David Hildenbrand <david@redhat.com> wrote:
>>
>> On 17.08.2018 10:41, Greg Kroah-Hartman wrote:
>>> On Fri, Aug 17, 2018 at 09:59:00AM +0200, David Hildenbrand wrote:
>>>> From: Vitaly Kuznetsov <vkuznets@redhat.com>
>>>>
>>>> Well require to call add_memory()/add_memory_resource() with
>>>> device_hotplug_lock held, to avoid a lock inversion. Allow external modules
>>>> (e.g. hv_balloon) that make use of add_memory()/add_memory_resource() to
>>>> lock device hotplug.
>>>>
>>>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>>>> [modify patch description]
>>>> Signed-off-by: David Hildenbrand <david@redhat.com>
>>>> ---
>>>> drivers/base/core.c | 2 ++
>>>> 1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/drivers/base/core.c b/drivers/base/core.c
>>>> index 04bbcd779e11..9010b9e942b5 100644
>>>> --- a/drivers/base/core.c
>>>> +++ b/drivers/base/core.c
>>>> @@ -700,11 +700,13 @@ void lock_device_hotplug(void)
>>>> {
>>>> mutex_lock(&device_hotplug_lock);
>>>> }
>>>> +EXPORT_SYMBOL_GPL(lock_device_hotplug);
>>>>
>>>> void unlock_device_hotplug(void)
>>>> {
>>>> mutex_unlock(&device_hotplug_lock);
>>>> }
>>>> +EXPORT_SYMBOL_GPL(unlock_device_hotplug);
>>>
>>> If these are going to be "global" symbols, let's properly name them.
>>> device_hotplug_lock/unlock would be better. But I am _really_ nervous
>>> about letting stuff outside of the driver core mess with this, as people
>>> better know what they are doing.
>>
>> The only "problem" is that we have kernel modules (for paravirtualized
>> devices) that call add_memory(). This is Hyper-V right now, but we might
>> have other ones in the future. Without them we would not have to export
>> it. We might also get kernel modules that want to call remove_memory() -
>> which will require the device_hotplug_lock as of now.
>>
>> What we could do is
>>
>> a) add_memory() -> _add_memory() and don't export it
>> b) add_memory() takes the device_hotplug_lock and calls _add_memory() .
>> We export that one.
>> c) Use add_memory() in external modules only
>>
>> Similar wrapper would be needed e.g. for remove_memory() later on.
>
> That would be safer IMO, as it would prevent developers from using
> add_memory() without the lock, say.
>
> If the lock is always going to be required for add_memory(), make it
> hard (or event impossible) to use the latter without it.
>
If there are no objections, I'll go into that direction. But I'll wait
for more comments regarding the general concept first.
Thanks!
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2018-08-17 9:41 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-17 7:58 [PATCH RFC 0/2] mm: online/offline_pages called w.o. mem_hotplug_lock David Hildenbrand
2018-08-17 7:59 ` [PATCH RFC 1/2] drivers/base: export lock_device_hotplug/unlock_device_hotplug David Hildenbrand
2018-08-17 8:41 ` Greg Kroah-Hartman
2018-08-17 8:56 ` David Hildenbrand
2018-08-17 9:03 ` Rafael J. Wysocki
2018-08-17 9:41 ` David Hildenbrand [this message]
2018-08-17 10:06 ` Greg Kroah-Hartman
2018-08-17 11:04 ` David Hildenbrand
2018-08-17 11:28 ` Heiko Carstens
2018-08-17 11:56 ` David Hildenbrand
2018-08-17 17:02 ` Greg Kroah-Hartman
2018-08-17 8:57 ` Rafael J. Wysocki
2018-08-17 7:59 ` [PATCH RFC 2/2] mm/memory_hotplug: fix online/offline_pages called w.o. mem_hotplug_lock David Hildenbrand
2018-08-17 8:20 ` Rafael J. Wysocki
2018-08-17 8:27 ` David Hildenbrand
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