linux-kernel - Re: [PATCH v1] drivers/base/memory.c: Don't access uninitialized memmaps in soft_offline_page

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Date:   Fri, 11 Oct 2019 11:51:46 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v1] drivers/base/memory.c: Don't access uninitialized
 memmaps in soft_offline_page_store()

On 11.10.19 08:13, Naoya Horiguchi wrote:
> On Thu, Oct 10, 2019 at 04:12:00PM +0200, David Hildenbrand wrote:
>> Uninitialized memmaps contain garbage and in the worst case trigger kernel
>> BUGs, especially with CONFIG_PAGE_POISONING. They should not get
>> touched.
>>
>> Right now, when trying to soft-offline a PFN that resides on a memory
>> block that was never onlined, one gets a misleading error with
>> CONFIG_PAGE_POISONING:
>>    :/# echo 5637144576 > /sys/devices/system/memory/soft_offline_page
>>    [   23.097167] soft offline: 0x150000 page already poisoned
>>
>> But the actual result depends on the garbage in the memmap.
>>
>> soft_offline_page() can only work with online pages, it returns -EIO in
>> case of ZONE_DEVICE. Make sure to only forward pages that are online
>> (iow, managed by the buddy) and, therefore, have an initialized memmap.
>>
>> Add a check against pfn_to_online_page() and similarly return -EIO.
>>
>> Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online") # visible after d0dc12e86b319
>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
>> Cc: Michal Hocko <mhocko@...nel.org>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Signed-off-by: David Hildenbrand <david@...hat.com>
>> ---
>>   drivers/base/memory.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
>> index 6bea4f3f8040..55907c27075b 100644
>> --- a/drivers/base/memory.c
>> +++ b/drivers/base/memory.c
>> @@ -540,6 +540,9 @@ static ssize_t soft_offline_page_store(struct device *dev,
>>   	pfn >>= PAGE_SHIFT;
>>   	if (!pfn_valid(pfn))
>>   		return -ENXIO;
>> +	/* Only online pages can be soft-offlined (esp., not ZONE_DEVICE). */
>> +	if (!pfn_to_online_page(pfn))
>> +		return -EIO;
> 
> Acked-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> 
> I think this check could be placed in soft_offline_page(), but that requires
> a few more unrelated lines of changes due to the mismatch on type of parameter
> between memory_failure() and soft_offline_page(),  This is not your problem,
> and I plan to do some cleanup on related interfaces, so this patch is fine.
> 

Thanks,

well I think when you come via madvise(), you are always guaranteed to  
hold a reasonable page in your hands. Only when converting from  
arbitrary pfns, we have to watch out. But yeah, feel free to cc me on  
cleanups :)

> - Naoya Horiguchi
> 


-- 

Thanks,

David / dhildenb