在 2024/7/30 15:45, David Hildenbrand 写道:
Looking at this in more detail, I wonder if we can turn that to
if (!folio_test_clear_lru(folio)) return; folio_get(folio);
In all cases? The caller must hold a reference, so this should be fine.
Seems the caller madvise_free_pte_range(...), calling folio_mark_lazyfree(...), doesn't hold a reference on folio.
If that would be the case and the folio could get freed concurrently, the folio_get(folio) would be completely broken.
In madvise_free_pte_range() we hold the PTL, so the folio cannot get freed concurrently.
Right.
folio_get() is only allowed when we are sure the folio cannot get freed concurrently, because we know there is a reference that cannot go away.
When cpu0 runs folio_activate(), and cpu1 runs folio_put() concurrently, a possible bad scenario would like:
cpu0 cpu1
folio_put_testzero(folio) if (!folio_test_clear_lru(folio))// Seems folio shouldn't be accessed
return; folio_get(folio); __folio_put(folio) __folio_clear_lru(folio)
Seems we should use folio_try_get(folio) instead of folio_get(folio).