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

From: Dmitry Osipenko <digetx-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
To: Wei Yang <richardw.yang-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
Cc: Russell King - ARM Linux
	<linux-I+IVW8TIWO2tmTQ+vhA3Yw@public.gmane.org>,
	akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org,
	dan.j.williams-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org,
	aneesh.kumar-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org,
	kirill-oKw7cIdHH8eLwutG50LtGA@public.gmane.org,
	yang.shi-KPsoFbNs7GizrGE5bRqYAgC/G2K4zDHf@public.gmane.org,
	thellstrom-pghWNbHTmq7QT0dZR+AlfA@public.gmane.org,
	Thierry Reding
	<thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org,
	"linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	"linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org"
	<linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>
Subject: Re: [PATCH 3/5] mm/mremap: use pmd_addr_end to calculate next in move_page_tables()
Date: Wed, 29 Jan 2020 02:35:25 +0300	[thread overview]
Message-ID: <27b70b0c-7945-cc85-8321-d9e4b6f17865@gmail.com> (raw)
In-Reply-To: <20200128232907.GA11467@richard>

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-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
>>>>> ---
>>>>>  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.