(I do have doubts about Barry's: the "_new" in folio_add_new_anon_rmap()
was all about optimizing a known-exclusive case, so it surprises me
to see it being extended to non-exclusive; and I worry over how its
atomic_set(&page->_mapcount, 0)s can be safe when non-exclusive (but
I've never caught up with David's exclusive changes, I'm out of date).
We discussed that a while ago: if we wouldn't be holding the folio lock
in the "folio == swapcache" at that point (which we do for both
do_swap_page() and unuse_pte()) things would already be pretty broken.
That's I added a while ago:
if (unlikely(!folio_test_anon(folio))) {
VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio);
/*
* For a PTE-mapped large folio, we only know that the single
* PTE is exclusive. Further, __folio_set_anon() might not get
* folio->index right when not given the address of the head
* page.
*/
...
We should probably move that VM_WARN_ON_FOLIO() to
folio_add_new_anon_rmap() and document that it's required in the
non-exclusive case.
But even if those are wrong, I'd expect them to tend towards a mapped
page becoming unreclaimable, then "Bad page map" when munmapped,
not to any of the double-free symptoms I've actually seen.)
What's the first known-good commit?
--
Cheers,
David / dhildenb
