Suren,
Sorry to review so late.
On Fri, Sep 22, 2023 at 06:31:44PM -0700, Suren Baghdasaryan wrote:
diff --git a/mm/rmap.c b/mm/rmap.c index ec7f8e6c9e48..c1ebbd23fa61 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -542,6 +542,7 @@ struct anon_vma *folio_lock_anon_vma_read(struct folio *folio, struct anon_vma *root_anon_vma; unsigned long anon_mapping; +repeat: rcu_read_lock(); anon_mapping = (unsigned long)READ_ONCE(folio->mapping); if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON) @@ -586,6 +587,18 @@ struct anon_vma *folio_lock_anon_vma_read(struct folio *folio, rcu_read_unlock(); anon_vma_lock_read(anon_vma);
- /*
* Check if UFFDIO_REMAP changed the anon_vma. This is needed* because we don't assume the folio was locked.*/- if (unlikely((unsigned long) READ_ONCE(folio->mapping) !=
anon_mapping)) {anon_vma_unlock_read(anon_vma);put_anon_vma(anon_vma);anon_vma = NULL;goto repeat;- }
We have an open-coded fast path above this:
if (down_read_trylock(&root_anon_vma->rwsem)) { /* * If the folio is still mapped, then this anon_vma is still * its anon_vma, and holding the mutex ensures that it will * not go away, see anon_vma_free(). */ if (!folio_mapped(folio)) { up_read(&root_anon_vma->rwsem); anon_vma = NULL; } goto out; }
Would that also need such check?
- if (atomic_dec_and_test(&anon_vma->refcount)) { /*
- Oops, we held the last refcount, release the lock
-- 2.42.0.515.g380fc7ccd1-goog