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

[Zi Yan <ziy@nvidia.com>]

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/

Best Regards,
Yan, Zi