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Fix potential GC issue while iterating over weak refs 

While walking over the list of subclasses for `include` and friends, we
check whether the subclass is a garbage object. After the check, we
allocate objects which might trigger GC and make the subclass garbage,
even though before the allocation the subclass was not garbage. This is
a sort of time-of-check-time-of-use issue.

Fix this by saving the weak reference to a local variable, upgrading it
to a strong reference while we do the allocation. It makes the code look
slightly nicer even if it doesn't fix any runtime issues.
This commit is contained in:
Alan Wu 2022-05-05 16:08:24 -04:00
parent 4acafdf632
commit 7448afccb3
Notes: git 2022-05-06 06:37:33 +09:00 
Merged: https://github.com/ruby/ruby/pull/5890
1 changed files with 9 additions and 8 deletions
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17
class.c
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@ -1383,17 +1383,18 @@ rb_prepend_module(VALUE klass, VALUE module)
/* During lazy sweeping, iclass->klass could be a dead object that
* has not yet been swept. */
if (!rb_objspace_garbage_object_p(iclass->klass)) {
if (klass_had_no_origin && klass_origin_m_tbl == RCLASS_M_TBL(iclass->klass)) {
const VALUE subclass = iclass->klass;
if (klass_had_no_origin && klass_origin_m_tbl == RCLASS_M_TBL(subclass)) {
// backfill an origin iclass to handle refinements and future prepends
rb_id_table_foreach(RCLASS_M_TBL(iclass->klass), clear_module_cache_i, (void *)iclass->klass);
RCLASS_M_TBL(iclass->klass) = klass_m_tbl;
VALUE origin = rb_include_class_new(klass_origin, RCLASS_SUPER(iclass->klass));
RCLASS_SET_SUPER(iclass->klass, origin);
RCLASS_SET_INCLUDER(origin, RCLASS_INCLUDER(iclass->klass));
RCLASS_SET_ORIGIN(iclass->klass, origin);
rb_id_table_foreach(RCLASS_M_TBL(subclass), clear_module_cache_i, (void *)subclass);
RCLASS_M_TBL(subclass) = klass_m_tbl;
VALUE origin = rb_include_class_new(klass_origin, RCLASS_SUPER(subclass));
RCLASS_SET_SUPER(subclass, origin);
RCLASS_SET_INCLUDER(origin, RCLASS_INCLUDER(subclass));
RCLASS_SET_ORIGIN(subclass, origin);
RICLASS_SET_ORIGIN_SHARED_MTBL(origin);
}
include_modules_at(iclass->klass, iclass->klass, module, FALSE);
include_modules_at(subclass, subclass, module, FALSE);
}
iclass = iclass->next;