linux-kernel - Re: [PATCH 3/5] mm/mremap: use pmd_addr_end to calculate next in move_page

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Date:   Wed, 29 Jan 2020 08:28:38 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Wei Yang <richardw.yang@...ux.intel.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        akpm@...ux-foundation.org, dan.j.williams@...el.com,
        aneesh.kumar@...ux.ibm.com, kirill@...temov.name,
        yang.shi@...ux.alibaba.com, thellstrom@...are.com,
        Thierry Reding <thierry.reding@...il.com>,
        Jon Hunter <jonathanh@...dia.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/5] mm/mremap: use pmd_addr_end to calculate next in
 move_page_tables()

On Wed, Jan 29, 2020 at 02:35:25AM +0300, Dmitry Osipenko wrote:
>29.01.2020 02:29, Wei Yang пишет:
>> On Tue, Jan 28, 2020 at 06:59:48PM +0300, Dmitry Osipenko wrote:
>>> 28.01.2020 03:43, Wei Yang пишет:
>>>> On Sun, Jan 26, 2020 at 05:47:57PM +0300, Dmitry Osipenko wrote:
>>>>> 18.01.2020 02:22, Wei Yang пишет:
>>>>>> Use the general helper instead of do it by hand.
>>>>>>
>>>>>> Signed-off-by: Wei Yang <richardw.yang@...ux.intel.com>
>>>>>> ---
>>>>>>  mm/mremap.c | 7 ++-----
>>>>>>  1 file changed, 2 insertions(+), 5 deletions(-)
>>>>>>
>>>>>> diff --git a/mm/mremap.c b/mm/mremap.c
>>>>>> index c2af8ba4ba43..a258914f3ee1 100644
>>>>>> --- a/mm/mremap.c
>>>>>> +++ b/mm/mremap.c
>>>>>> @@ -253,11 +253,8 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
>>>>>>  
>>>>>>  	for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
>>>>>>  		cond_resched();
>>>>>> -		next = (old_addr + PMD_SIZE) & PMD_MASK;
>>>>>> -		/* even if next overflowed, extent below will be ok */
>>>>>> +		next = pmd_addr_end(old_addr, old_end);
>>>>>>  		extent = next - old_addr;
>>>>>> -		if (extent > old_end - old_addr)
>>>>>> -			extent = old_end - old_addr;
>>>>>>  		old_pmd = get_old_pmd(vma->vm_mm, old_addr);
>>>>>>  		if (!old_pmd)
>>>>>>  			continue;
>>>>>> @@ -301,7 +298,7 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
>>>>>>  
>>>>>>  		if (pte_alloc(new_vma->vm_mm, new_pmd))
>>>>>>  			break;
>>>>>> -		next = (new_addr + PMD_SIZE) & PMD_MASK;
>>>>>> +		next = pmd_addr_end(new_addr, new_addr + len);
>>>>>>  		if (extent > next - new_addr)
>>>>>>  			extent = next - new_addr;
>>>>>>  		move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma,
>>>>>>
>>>>>
>>>>> Hello Wei,
>>>>>
>>>>> Starting with next-20200122, I'm seeing the following in KMSG on NVIDIA
>>>>> Tegra (ARM32):
>>>>>
>>>>>  BUG: Bad rss-counter state mm:(ptrval) type:MM_ANONPAGES val:190
>>>>>
>>>>
>>>> Thanks.
>>>>
>>>> Would you mind letting me know which case you are testing?
>>>
>>> Nothing special, systemd starts to fall apart during boot.
>>>
>>>> Or the special thing is 32-bit platform?
>>> I have a limited knowledge about mm/, so can't provide detailed explanation.
>>>
>>> Please take a look at this:
>>>
>>> [1]
>>> https://elixir.bootlin.com/linux/v5.5/source/arch/arm/include/asm/pgtable-2level.h#L210
>>>
>>> [2]
>>> https://elixir.bootlin.com/linux/v5.5/source/include/asm-generic/pgtable.h#L549
>>>
>>> [3]
>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c0ba10b512eb2e2a3888b6e6cc0e089f5e7a191b
>> 
>> Thanks, I see the difference here.
>> 
>> If this is the case, we can't use pmd_addr_end() to simplify the calculation.
>> This changes the behavior.
>> 
>> I would prepare another patch set to fix this. Would you mind helping me
>> verify on your platform?
>
>Sure, please feel free to CC me on that patch.

Thanks, you are in the cc list of v2.

Hope this one works fine on ARM.

-- 
Wei Yang
Help you, Help me