From 3471ee0749be4bf9bfdd382ac0b6aedaf47a53b1 Mon Sep 17 00:00:00 2001 From: John Hawthorn Date: Fri, 13 Jun 2025 18:52:32 -0700 Subject: [PATCH] Fix generic_ivar_set_shape_ivptr for table rebuild [Bug #21438] Previously GC could trigger a table rebuild of the generic ivar st_table in the middle of calling the st_update callback. This could cause entries to be reallocated or rearranged and the update to be for the wrong entry. This commit adds an assertion to make that case easier to detect, and replaces the st_update with a separate st_lookup and st_insert. Also free after insert in generic_ivar_set_shape_ivptr Previously we were performing a realloc and then inserting the new value into the table. If the table was flagged as requiring a rebuild, this could trigger GC work and marking within that GC could access the ivptr freed by realloc. Co-authored-by: Aaron Patterson Co-authored-by: Jean Boussier --- st.c | 9 ++++ test/ruby/test_variable.rb | 22 ++++++++- variable.c | 96 +++++++++++++++++--------------------- 3 files changed, 71 insertions(+), 56 deletions(-) diff --git a/st.c b/st.c index 50bfd4bfbb..ab361e1ca8 100644 --- a/st.c +++ b/st.c @@ -1482,7 +1482,16 @@ st_update(st_table *tab, st_data_t key, value = entry->record; } old_key = key; + + unsigned int rebuilds_num = tab->rebuilds_num; + retval = (*func)(&key, &value, arg, existing); + + // We need to make sure that the callback didn't cause a table rebuild + // Ideally we would make sure no operations happened + assert(rebuilds_num == tab->rebuilds_num); + (void)rebuilds_num; + switch (retval) { case ST_CONTINUE: if (! existing) { diff --git a/test/ruby/test_variable.rb b/test/ruby/test_variable.rb index 86f2e4bb84..fc2580654d 100644 --- a/test/ruby/test_variable.rb +++ b/test/ruby/test_variable.rb @@ -393,20 +393,38 @@ class TestVariable < Test::Unit::TestCase @a = 1 @b = 2 @c = 3 + @d = 4 + @e = 5 + @f = 6 + @g = 7 + @h = 8 end def ivars - [@a, @b, @c] + [@a, @b, @c, @d, @e, @f, @g, @h] end end def test_external_ivars 3.times{ # check inline cache for external ivar access - assert_equal [1, 2, 3], ExIvar.new.ivars + assert_equal [1, 2, 3, 4, 5, 6, 7, 8], ExIvar.new.ivars } end + def test_exivar_resize_with_compaction_stress + objs = 10_000.times.map do + ExIvar.new + end + EnvUtil.under_gc_compact_stress do + 10.times do + x = ExIvar.new + x.instance_variable_set(:@resize, 1) + x + end + end + end + def test_local_variables_with_kwarg bug11674 = '[ruby-core:71437] [Bug #11674]' v = with_kwargs_11(v1:1,v2:2,v3:3,v4:4,v5:5,v6:6,v7:7,v8:8,v9:9,v10:10,v11:11) diff --git a/variable.c b/variable.c index f8cf7d735e..6161873a60 100644 --- a/variable.c +++ b/variable.c @@ -1162,22 +1162,6 @@ gen_ivtbl_bytes(size_t n) return offsetof(struct gen_ivtbl, as.shape.ivptr) + n * sizeof(VALUE); } -static struct gen_ivtbl * -gen_ivtbl_resize(struct gen_ivtbl *old, uint32_t n) -{ - RUBY_ASSERT(n > 0); - - uint32_t len = old ? old->as.shape.numiv : 0; - struct gen_ivtbl *ivtbl = xrealloc(old, gen_ivtbl_bytes(n)); - - ivtbl->as.shape.numiv = n; - for (; len < n; len++) { - ivtbl->as.shape.ivptr[len] = Qundef; - } - - return ivtbl; -} - void rb_mark_generic_ivar(VALUE obj) { @@ -1632,41 +1616,6 @@ struct gen_ivar_lookup_ensure_size { bool resize; }; -static int -generic_ivar_lookup_ensure_size(st_data_t *k, st_data_t *v, st_data_t u, int existing) -{ - ASSERT_vm_locking(); - - struct gen_ivar_lookup_ensure_size *ivar_lookup = (struct gen_ivar_lookup_ensure_size *)u; - struct gen_ivtbl *ivtbl = existing ? (struct gen_ivtbl *)*v : NULL; - - if (!existing || ivar_lookup->resize) { - if (existing) { - RUBY_ASSERT(ivar_lookup->shape->type == SHAPE_IVAR); - RUBY_ASSERT(rb_shape_get_shape_by_id(ivar_lookup->shape->parent_id)->capacity < ivar_lookup->shape->capacity); - } - else { - FL_SET_RAW((VALUE)*k, FL_EXIVAR); - } - - ivtbl = gen_ivtbl_resize(ivtbl, ivar_lookup->shape->capacity); - *v = (st_data_t)ivtbl; - } - - RUBY_ASSERT(FL_TEST((VALUE)*k, FL_EXIVAR)); - - ivar_lookup->ivtbl = ivtbl; - if (ivar_lookup->shape) { -#if SHAPE_IN_BASIC_FLAGS - rb_shape_set_shape(ivar_lookup->obj, ivar_lookup->shape); -#else - ivtbl->shape_id = rb_shape_id(ivar_lookup->shape); -#endif - } - - return ST_CONTINUE; -} - static VALUE * generic_ivar_set_shape_ivptr(VALUE obj, void *data) { @@ -1674,9 +1623,48 @@ generic_ivar_set_shape_ivptr(VALUE obj, void *data) struct gen_ivar_lookup_ensure_size *ivar_lookup = data; + // We can't use st_update, since when resizing the fields table GC can + // happen, which will modify the st_table and may rebuild it RB_VM_LOCK_ENTER(); { - st_update(generic_ivtbl(obj, ivar_lookup->id, false), (st_data_t)obj, generic_ivar_lookup_ensure_size, (st_data_t)ivar_lookup); + struct gen_ivtbl *ivtbl = NULL; + st_table *tbl = generic_ivtbl(obj, ivar_lookup->id, false); + int existing = st_lookup(tbl, (st_data_t)obj, (st_data_t *)&ivtbl); + + if (!existing || ivar_lookup->resize) { + uint32_t new_capa = ivar_lookup->shape->capacity; + uint32_t old_capa = rb_shape_get_shape_by_id(ivar_lookup->shape->parent_id)->capacity; + + if (existing) { + RUBY_ASSERT(ivar_lookup->shape->type == SHAPE_IVAR); + RUBY_ASSERT(old_capa < new_capa); + RUBY_ASSERT(ivtbl); + } else { + RUBY_ASSERT(!ivtbl); + RUBY_ASSERT(old_capa == 0); + } + RUBY_ASSERT(new_capa > 0); + + struct gen_ivtbl *old_ivtbl = ivtbl; + ivtbl = xmalloc(gen_ivtbl_bytes(new_capa)); + if (old_ivtbl) { + memcpy(ivtbl, old_ivtbl, gen_ivtbl_bytes(old_capa)); + } + ivtbl->as.shape.numiv = new_capa; + for (uint32_t i = old_capa; i < new_capa; i++) { + ivtbl->as.shape.ivptr[i] = Qundef; + } + + st_insert(tbl, (st_data_t)obj, (st_data_t)ivtbl); + if (old_ivtbl) { + xfree(old_ivtbl); + } + } + + ivar_lookup->ivtbl = ivtbl; + if (ivar_lookup->shape) { + rb_shape_set_shape(ivar_lookup->obj, ivar_lookup->shape); + } } RB_VM_LOCK_LEAVE(); @@ -2134,8 +2122,8 @@ rb_copy_generic_ivar(VALUE clone, VALUE obj) new_ivtbl->as.complex.table = st_copy(obj_ivtbl->as.complex.table); } else { - new_ivtbl = gen_ivtbl_resize(0, obj_ivtbl->as.shape.numiv); - + new_ivtbl = xmalloc(gen_ivtbl_bytes(obj_ivtbl->as.shape.numiv)); + new_ivtbl->as.shape.numiv = obj_ivtbl->as.shape.numiv; for (uint32_t i=0; ias.shape.numiv; i++) { RB_OBJ_WRITE(clone, &new_ivtbl->as.shape.ivptr[i], obj_ivtbl->as.shape.ivptr[i]); }