Subject: Re: [PATCH 3/5] mm/mremap: use pmd_addr_end to calculate next in move_page_tables()

From: Wei Yang <[email-masked]>
Date: Wed, 29 Jan 2020 07:29:07 +0800

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 <[email-masked]>
>>>> ---
>>>>  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?

-- 
Wei Yang
Help you, Help me

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