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Fix GC race condition in autoload.

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This commit is contained in:
Samuel Williams 2022-05-25 23:12:54 +12:00
parent cd6f87eefc
commit d875445e8a
Notes: git 2022-05-25 21:18:01 +09:00 
Merged: https://github.com/ruby/ruby/pull/5941
2 changed files with 19 additions and 15 deletions
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1
test/ruby/test_autoload.rb
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@ -529,6 +529,7 @@ p Foo::Bar
t2 = Thread.new {Bar} t2 = Thread.new {Bar}
t1.join t1.join
GC.start # force GC.
t2.join t2.join
Object.send(:remove_const, :Foo) Object.send(:remove_const, :Foo)

33
variable.c
View File

@ -2669,12 +2669,6 @@ autoload_try_load(VALUE _arguments)
{ {
struct autoload_load_arguments *arguments = (struct autoload_load_arguments*)_arguments; struct autoload_load_arguments *arguments = (struct autoload_load_arguments*)_arguments;
// We have tried to require the autoload feature, so we shouldn't bother trying again in any
// other threads. More specifically, `arguments->result` starts of as nil, but then contains the
// result of `require` which is either true or false. Provided it's not nil, it means some other
// thread has got as far as evaluating the require statement completely.
if (arguments->result != Qnil) return arguments->result;
// Try to require the autoload feature: // Try to require the autoload feature:
rb_ensure(autoload_feature_require, _arguments, autoload_feature_require_ensure, _arguments); rb_ensure(autoload_feature_require, _arguments, autoload_feature_require_ensure, _arguments);
@ -2722,7 +2716,15 @@ rb_autoload_load(VALUE module, ID name)
arguments.flag = ce->flag & (CONST_DEPRECATED | CONST_VISIBILITY_MASK); arguments.flag = ce->flag & (CONST_DEPRECATED | CONST_VISIBILITY_MASK);
// Only one thread will enter here at a time: // Only one thread will enter here at a time:
return rb_mutex_synchronize(arguments.mutex, autoload_try_load, (VALUE)&arguments); VALUE result = rb_mutex_synchronize(arguments.mutex, autoload_try_load, (VALUE)&arguments);
// If you don't guard this value, it's possible for the autoload constant to
// be freed by another thread which loads multiple constants, one of which
// resolves to the constant this thread is trying to load, so proteect this
// so that it is not freed until we are done with it in `autoload_try_load`:
RB_GC_GUARD(autoload_const_value);
return result;
} }
VALUE VALUE
@ -3312,18 +3314,19 @@ rb_const_set(VALUE klass, ID id, VALUE val)
} }
static struct autoload_data * static struct autoload_data *
autoload_data_for_named_constant(VALUE mod, ID id, struct autoload_const **acp) autoload_data_for_named_constant(VALUE module, ID name, struct autoload_const **autoload_const_pointer)
{ {
struct autoload_data *ele; VALUE autoload_data_value = autoload_data(module, name);
VALUE load = autoload_data(mod, id); if (!autoload_data_value) return 0;
if (!load) return 0;
ele = get_autoload_data(load, acp); struct autoload_data *autoload_data = get_autoload_data(autoload_data_value, autoload_const_pointer);
if (!ele) return 0; if (!autoload_data) return 0;
/* for autoloading thread, keep the defined value to autoloading storage */ /* for autoloading thread, keep the defined value to autoloading storage */
if (autoload_by_current(ele)) { if (autoload_by_current(autoload_data)) {
return ele; return autoload_data;
} }
return 0; return 0;
} }