From: David Hildenbrand <david@redhat.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v2 2/2] mm/memory-failure.c: Don't access uninitialized memmaps in memory_failure()
Date: Thu, 10 Oct 2019 09:52:20 +0200 [thread overview]
Message-ID: <18383432-c74a-9ce5-a3c6-1e57d54cb629@redhat.com> (raw)
In-Reply-To: <20191010073526.GC18412@dhcp22.suse.cz>
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@ah.jp.nec.com>
>>>> Cc: Andrew Morton <akpm@linux-foundation.org>
>>>> Cc: Michal Hocko <mhocko@kernel.org>
>>>> Signed-off-by: David Hildenbrand <david@redhat.com>
>>>> ---
>>>> 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.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2019-10-10 7:52 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-09 14:24 [PATCH v2 0/2] mm: Don't access uninitialized memmaps in PFN walkers David Hildenbrand
2019-10-09 14:24 ` [PATCH v2 1/2] mm: Don't access uninitialized memmaps in fs/proc/page.c David Hildenbrand
2019-10-09 14:41 ` Michal Hocko
2019-10-14 8:44 ` David Hildenbrand
2019-10-09 14:24 ` [PATCH v2 2/2] mm/memory-failure.c: Don't access uninitialized memmaps in memory_failure() David Hildenbrand
2019-10-09 14:43 ` Michal Hocko
2019-10-10 7:27 ` David Hildenbrand
2019-10-10 7:35 ` Michal Hocko
2019-10-10 7:52 ` David Hildenbrand [this message]
2019-10-10 7:58 ` David Hildenbrand
2019-10-11 6:02 ` Naoya Horiguchi
2019-10-11 10:13 ` David Hildenbrand
2019-10-14 13:36 ` Michal Hocko
2019-10-15 14:23 ` Oscar Salvador
2019-10-10 0:26 ` Naoya Horiguchi
2019-10-10 7:17 ` David Hildenbrand
2019-10-11 6:50 ` Naoya Horiguchi
2019-10-19 2:05 ` Andrew Morton
2019-10-21 9:44 ` David Hildenbrand
2019-10-14 8:41 ` David Hildenbrand
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