Re: [syzbot] [mm?] WARNING in folio_remove_rmap_ptes

[David Hildenbrand (Red Hat)]

On 1/1/26 17:32, Lorenzo Stoakes wrote:
> On Thu, Jan 01, 2026 at 11:30:52PM +0900, Jeongjun Park wrote:
> > Based on my testing, I found that the WARNING starts from commit
> > d23cb648e365 ("mm/mremap: permit mremap() move of multiple VMAs"),
> > which is right after commit 2cf442d74216 ("mm/mremap: clean up mlock
> > populate behavior") in Lorenzo's mremap-related patch series.
>
> OK let me take a look.

Trying to make sense of the reproducer and how bpf comes into play ... I 
assume BPF is only used to install a uprobe.

We seem to create a file0 and register a uprobe on it.

We then mmap() that file with PROT_NONE. We should end up in 
uprobe_mmap() and trigger a COW fault -> allocate an anon_vma.

So likely the bpf magic is only there to allocate an anon_vma for a 
PROT_NONE region.

But it's all a bit confusing ... :)

--
Cheers

David