On 10.10.19 09:52, David Hildenbrand wrote:
> On 10.10.19 09:35, Michal Hocko wrote:
>> On Thu 10-10-19 09:27:32, David Hildenbrand wrote:
>>> On 09.10.19 16:43, Michal Hocko wrote:
>>>> On Wed 09-10-19 16:24:35, David Hildenbrand wrote:
>>>>> We should check for pfn_to_online_page() to not access uninitialized
>>>>> memmaps. Reshuffle the code so we don't have to duplicate the error
>>>>> message.
>>>>>
>>>>> Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
>>>>> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>>>>> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
>>>>> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
>>>>> ---
>>>>> mm/memory-failure.c | 14 ++++++++------
>>>>> 1 file changed, 8 insertions(+), 6 deletions(-)
>>>>>
>>>>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
>>>>> index 7ef849da8278..e866e6e5660b 100644
>>>>> --- a/mm/memory-failure.c
>>>>> +++ b/mm/memory-failure.c
>>>>> @@ -1253,17 +1253,19 @@ int memory_failure(unsigned long pfn, int flags)
>>>>> if (!sysctl_memory_failure_recovery)
>>>>> panic("Memory failure on page %lx", pfn);
>>>>>
>>>>> - if (!pfn_valid(pfn)) {
>>>>> + p = pfn_to_online_page(pfn);
>>>>> + if (!p) {
>>>>> + if (pfn_valid(pfn)) {
>>>>> + pgmap = get_dev_pagemap(pfn, NULL);
>>>>> + if (pgmap)
>>>>> + return memory_failure_dev_pagemap(pfn, flags,
>>>>> + pgmap);
>>>>> + }
>>>>> pr_err("Memory failure: %#lx: memory outside kernel control\n",
>>>>> pfn);
>>>>> return -ENXIO;
>>>>
>>>> Don't we need that earlier at hwpoison_inject level?
>>>>
>>>
>>> Theoretically yes, this is another instance. But pfn_to_online_page(pfn)
>>> alone would not be sufficient as discussed. We would, again, have to
>>> special-case ZONE_DEVICE via things like get_dev_pagemap() ...
>>>
>>> But mm/hwpoison-inject.c:hwpoison_inject() is a pure debug feature either way:
>>>
>>> /*
>>> * Note that the below poison/unpoison interfaces do not involve
>>> * hardware status change, hence do not require hardware support.
>>> * They are mainly for testing hwpoison in software level.
>>> */
>>>
>>> So it's not that bad compared to memory_failure() called from real HW or
>>> drivers/base/memory.c:soft_offline_page_store()/hard_offline_page_store()
>>
>> Yes, this is just a toy. And yes we need to handle zone device pages
>> here because a) people likely want to test MCE behavior even on these
>> pages and b) HW can really trigger MCEs there as well. I was just
>> pointing that the patch is likely incomplete.
>>
>
> I rather think this deserves a separate patch as it is a separate
> interface :)
>
> I do wonder why hwpoison_inject() has to perform so much extra work
> compared to other memory_failure() users. This smells like legacy
> leftovers to me, but I might be wrong. The interface is fairly old,
> though. Does anybody know why we need this magic? I can spot quite some
> duplicate checks/things getting performed.
>
> Naiive me would just make the interface perform the same as
> hard_offline_page_store(). But most probably I am not getting the real
> purpose of both different interfaces.
>
> HWPOISON_INJECT is only selected for DEBUG_KERNEL, so I would have
> guessed that fixing this is not urgent.
>
> BTW: mm/memory-failure.c:soft_offline_page() also looks wrong and needs
> fixing to make sure we access initialized memmaps.
>
To be more precise, soft_offline_page_store() needs a
pfn_to_online_page() check. Will send a patch.
--
Thanks,
David / dhildenb
