Re: mm: Regression with v7.0-rc1 on RISC-V

[Ron Economos <re@w6rz.net>]

On 2/24/26 09:29, Zi Yan wrote:
> On 24 Feb 2026, at 12:17, Zi Yan wrote:
>
>> On 24 Feb 2026, at 12:14, Zi Yan wrote:
>>
>>> On 24 Feb 2026, at 12:07, David Hildenbrand wrote:
>>>
>>>>> David Hildenbrand (Arm) <david@kernel.org> hat am 24.02.2026 12:00 CET geschrieben:
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> On 2/24/26 09:37, Ron Economos wrote:
>>>>>
>>>>>> I'm getting a BUG dump during shutdown with Linux v7.0-rc1 on RISC-V.
>>>>>>
>>>>>>
>>>>>>
>>>>>> [  OK  ] Reached target shutdown.target - System Shutdown.
>>>>>>
>>>>>> [  OK  ] Reached target final.target - Late Shutdown Services.
>>>>>>
>>>>>> [  OK  ] Finished systemd-reboot.service - System Reboot.
>>>>>>
>>>>>> [  OK  ] Reached target reboot.target - System Reboot.
>>>>>>
>>>>>> [  173.985249] BUG: Bad page state in process shutdown  pfn:f8850
>>>>>>
>>>>>> [  173.985311] page: refcount:1 mapcount:0 mapping:0000000000000000
>>>>>>
>>>>>> index:0x0 pfn:0xf8850
>>>>>>
>>>>>> [  173.985336] flags: 0xffff80000000000(node=0|zone=0|
>>>>>>
>>>>>> lastcpupid=0x1ffff) CMA
>>>>>>
>>>>>> [  173.985365] raw: 0ffff80000000000 ffffffc501e21448 ffffffc600f2ae88
>>>>>>
>>>>>> 0000000000000000
>>>>>>
>>>>>> [  173.985386] raw: 0000000000000000 0000000000000000 00000001ffffffff
>>>>>>
>>>>>> 0000000000000000
>>>>>>
>>>>>> [  173.985403] page dumped because: nonzero _refcount
>>>>> So, we're freeing something from CMA in cma_release().
>>>>>
>>>>>
>>>>>
>>>>> In cma_release() we iterate all pages to decrement their refcount
>>>>>
>>>>>
>>>>>
>>>>> VM_WARN_ON(!put_page_testzero(pfn_to_page(pfn)));
>>>>>
>>>>>
>>>>>
>>>>> I would expect that this would fire already if there is still a page
>>>>>
>>>>> referenced.
>>>>>
>>>>>
>>>>>
>>>>> Are you running with CONFIG_DEBUG_VM=y ?
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>>
>>>>> Cheers,
>>>>>
>>>>>
>>>>>
>>>>> David
>>>> Thinking again without my computer at hand … isn‘t the call completely optimized out without CONFIG_DEBUG_VM?
>>>>
>>>>
>>>>
>>>> At least that’s what I remember.
>>> Right. Without CONFIG_DEBUG_VM=y, VM_WARN_ON(!put_page_testzero(pfn_to_page(pfn)))
>>> and is_check_pages_enabled(), which leads to free_page_is_bad()’s
>>> “page dumped because: nonzero _refcount”, are disabled.
>>>
>>> It seems to me that someone else bump the page refcount between
>>> VM_WARN_ON(!put_page_testzero(pfn_to_page(pfn))) and free_page_is_bad().
>>>
>> Merging Ron’s reply from another thread[1]:
>>
>> “Something strange is going on. I enabled CONFIG_DEBUG_VM by itself and
>> the issue went away. Let me try CONFIG_DEBUG_PAGE_REF.”
>>
>> Looks like something is racy, since it is reproducible reliably.
>>
>> [1] https://lore.kernel.org/all/30dd1efc-9bd9-4664-999e-610d181600f9@w6rz.net/
> VM_WARN_ON() is BUILD_BUG_ON_INVALID() when CONFIG_DEBUG_VM is off. Only
> the validity of the expression is checked and no code is generated.
> So that put_page_testzero() becomes a NOP.
>
> Hi Ron,
>
> Can you check if the patch below fix the issue without CONFIG_DEBUG_VM?
>
> diff --git a/mm/cma.c b/mm/cma.c
> index 94b5da468a7d..96be62eb3713 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -1020,8 +1020,11 @@ bool cma_release(struct cma *cma, const struct page *pages,
>   		return false;
>
>   	pfn = page_to_pfn(pages);
> -	for (i = 0; i < count; i++, pfn++)
> -		VM_WARN_ON(!put_page_testzero(pfn_to_page(pfn)));
> +	for (i = 0; i < count; i++, pfn++) {
> +		int __maybe_unused ret = put_page_testzero(pfn_to_page(pfn));
> +
> +		VM_WARN_ON(!ret);
> +	}
>
>   	__cma_release_frozen(cma, cmr, pages, count);
>
>
>
> Best Regards,
> Yan, Zi

Yes, that patch fixes the issue.