Re: [syzbot] [mm?] WARNING in __folio_rmap_sanity_checks (2)

[David Hildenbrand <david@redhat.com>]

On 11.01.25 02:00, Hillf Danton wrote:
> On Fri, 10 Jan 2025 17:35:25 +0100 David Hildenbrand <david@redhat.com>
>> On 31.12.24 09:41, Hillf Danton wrote:
>>> On Fri, 27 Dec 2024 20:56:21 -0800
>>>> syzbot has found a reproducer for the following issue on:
>>>>
>>>> HEAD commit:    8155b4ef3466 Add linux-next specific files for 20241220
>>>> git tree:       linux-next
>>>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1652fadf980000
>>>
>>> #syz test
>>>
>>> --- x/mm/filemap.c
>>> +++ y/mm/filemap.c
>>> @@ -3636,6 +3636,10 @@ static vm_fault_t filemap_map_folio_rang
>>>    		continue;
>>>    skip:
>>>    		if (count) {
>>> +			for (unsigned int i = 0; i < count; i++) {
>>> +				if (page_folio(page + i) != folio)
>>> +					goto out;
>>> +			}
>>
>> IIRC, count <= nr_pages. Wouldn't that mean that we somehow pass in
>> nr_pages that already exceeds the given folio+start?
>>
>> When I last looked at this, I was not able to spot the error in the
>> caller :(
>>
> This is a debug patch at the first place, and this hunk overlaps with the
> next one.

Yeah, I was rather wondering if you had any clue why that hunk might 
help on its own.

-- 
Cheers,

David / dhildenb