linux-kernel - Re: [PATCH -next] mm/hotplug: skip bad PFNs from pfn_to_online

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Date:   Thu, 13 Jun 2019 21:29:50 -0400
From:   Qian Cai <cai@....pw>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next] mm/hotplug: skip bad PFNs from pfn_to_online_page()



> On Jun 13, 2019, at 9:17 PM, Dan Williams <dan.j.williams@...el.com> wrote:
> 
> On Thu, Jun 13, 2019 at 11:42 AM Qian Cai <cai@....pw> wrote:
>> 
>> On Wed, 2019-06-12 at 12:37 -0700, Dan Williams wrote:
>>> On Wed, Jun 12, 2019 at 12:16 PM Qian Cai <cai@....pw> wrote:
>>>> 
>>>> The linux-next commit "mm/sparsemem: Add helpers track active portions
>>>> of a section at boot" [1] causes a crash below when the first kmemleak
>>>> scan kthread kicks in. This is because kmemleak_scan() calls
>>>> pfn_to_online_page(() which calls pfn_valid_within() instead of
>>>> pfn_valid() on x86 due to CONFIG_HOLES_IN_ZONE=n.
>>>> 
>>>> The commit [1] did add an additional check of pfn_section_valid() in
>>>> pfn_valid(), but forgot to add it in the above code path.
>>>> 
>>>> page:ffffea0002748000 is uninitialized and poisoned
>>>> raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff
>>>> raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff
>>>> page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
>>>> ------------[ cut here ]------------
>>>> kernel BUG at include/linux/mm.h:1084!
>>>> invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN PTI
>>>> CPU: 5 PID: 332 Comm: kmemleak Not tainted 5.2.0-rc4-next-20190612+ #6
>>>> Hardware name: Lenovo ThinkSystem SR530 -[7X07RCZ000]-/-[7X07RCZ000]-,
>>>> BIOS -[TEE113T-1.00]- 07/07/2017
>>>> RIP: 0010:kmemleak_scan+0x6df/0xad0
>>>> Call Trace:
>>>> kmemleak_scan_thread+0x9f/0xc7
>>>> kthread+0x1d2/0x1f0
>>>> ret_from_fork+0x35/0x4
>>>> 
>>>> [1] https://patchwork.kernel.org/patch/10977957/
>>>> 
>>>> Signed-off-by: Qian Cai <cai@....pw>
>>>> ---
>>>> include/linux/memory_hotplug.h | 1 +
>>>> 1 file changed, 1 insertion(+)
>>>> 
>>>> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
>>>> index 0b8a5e5ef2da..f02be86077e3 100644
>>>> --- a/include/linux/memory_hotplug.h
>>>> +++ b/include/linux/memory_hotplug.h
>>>> @@ -28,6 +28,7 @@
>>>>        unsigned long ___nr = pfn_to_section_nr(___pfn);           \
>>>>                                                                   \
>>>>        if (___nr < NR_MEM_SECTIONS && online_section_nr(___nr) && \
>>>> +           pfn_section_valid(__nr_to_section(___nr), pfn) &&      \
>>>>            pfn_valid_within(___pfn))                              \
>>>>                ___page = pfn_to_page(___pfn);                     \
>>>>        ___page;                                                   \
>>> 
>>> Looks ok to me:
>>> 
>>> Acked-by: Dan Williams <dan.j.williams@...el.com>
>>> 
>>> ...but why is pfn_to_online_page() a multi-line macro instead of a
>>> static inline like all the helper routines it invokes?
>> 
>> Sigh, probably because it is a mess over there.
>> 
>> memory_hotplug.h and mmzone.h are included each other. Converted it directly to
>> a static inline triggers compilation errors because mmzone.h was included
>> somewhere else and found pfn_to_online_page() needs things like
>> pfn_valid_within() and online_section_nr() etc which are only defined later in
>> mmzone.h.
> 
> Ok, makes sense I had I assumed it was something horrible like that.
> 
> Qian, can you send more details on the reproduction steps for the
> failures you are seeing? Like configs and platforms you're testing.
> I've tried enabling kmemleak and offlining memory and have yet to
> trigger these failures. I also have a couple people willing to help me
> out with tracking down the PowerPC issue, but I assume they need some
> help with the reproduction as well.

https://github.com/cailca/linux-mm

You can see the configs for each arch there. It was reproduced on several x86 NUMA bare-metal machines HPE, Lenovo etc either Intel or AMD. Check the “test.sh”, there is a part to do offline/online will reproduce it.

The powerpc is IBM 8335-GTC (ibm,witherspoon) POWER9 which is a NUMA PowerNV platform.