Re: WARNING in memory_failure() at include/linux/huge_mm.h:635 triggered

[David Hildenbrand (arm)]

On 2/4/26 18:41, Zi Yan wrote:
> On 4 Feb 2026, at 12:34, Zi Yan wrote:
>
> > On 4 Feb 2026, at 12:23, Zi Yan wrote:
> >
> > >  From the C repro above, syzbot opened a dev "/dev/sg#" and did mmap on it.
> > > Is it a device driver issue?
> >
> > OK, it is CONFIG_CHR_DEV_SG. And the driver allocates a compound page at[1].
> > Since we initialize folio fields in prep_compound_page(), it becomes a folio
> > when it is inserted into a VMA.
>
> More details:
> later at sg_vma_fault(), the driver just handles a page fault by supplying
> a subpage from a pre-allocated compound page[3]. We then get a large folio
> without !CONFIG_TRANSPARENT_HUGEPAGE.

We can identify such non-folio (but compound) things by looking at 
PG_large_rmappable IIRC.

--
Cheers,

David