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Make env_copy compaction safe

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The original order of events is:

1. Allocate env_body.
2. Fill env_body using elements in src_env, and it performs operations
   that can trigger a GC.
3. Create the copied_env using vm_env_new.

However, if GC compaction runs during step 2, then copied_env would not
have yet been created and objects on env_body could move but it would
not be reference updated.

This commit changes the the order to be (1), (3), (2).
This commit is contained in:
Peter Zhu 2023-12-04 14:02:56 -05:00
parent ed25f0bd5a
commit 674eb7df7f
1 changed files with 9 additions and 5 deletions
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14
vm.c
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@ -1218,6 +1218,13 @@ env_copy(const VALUE *src_ep, VALUE read_only_variables)
VALUE *env_body = ZALLOC_N(VALUE, src_env->env_size); // fill with Qfalse VALUE *env_body = ZALLOC_N(VALUE, src_env->env_size); // fill with Qfalse
VALUE *ep = &env_body[src_env->env_size - 2]; VALUE *ep = &env_body[src_env->env_size - 2];
ep[VM_ENV_DATA_INDEX_ME_CREF] = src_ep[VM_ENV_DATA_INDEX_ME_CREF];
ep[VM_ENV_DATA_INDEX_FLAGS] = src_ep[VM_ENV_DATA_INDEX_FLAGS] | VM_ENV_FLAG_ISOLATED;
if (!VM_ENV_LOCAL_P(src_ep)) {
VM_ENV_FLAGS_SET(ep, VM_ENV_FLAG_LOCAL);
}
const rb_env_t *copied_env = vm_env_new(ep, env_body, src_env->env_size, src_env->iseq);
volatile VALUE prev_env = Qnil; volatile VALUE prev_env = Qnil;
if (read_only_variables) { if (read_only_variables) {
@ -1237,7 +1244,7 @@ env_copy(const VALUE *src_ep, VALUE read_only_variables)
rb_str_cat_cstr(msg, "a hidden variable"); rb_str_cat_cstr(msg, "a hidden variable");
rb_exc_raise(rb_exc_new_str(rb_eRactorIsolationError, msg)); rb_exc_raise(rb_exc_new_str(rb_eRactorIsolationError, msg));
} }
env_body[j] = v; RB_OBJ_WRITE((VALUE)copied_env, &env_body[j], v);
rb_ary_delete_at(read_only_variables, i); rb_ary_delete_at(read_only_variables, i);
break; break;
} }
@ -1245,20 +1252,17 @@ env_copy(const VALUE *src_ep, VALUE read_only_variables)
} }
} }
ep[VM_ENV_DATA_INDEX_ME_CREF] = src_ep[VM_ENV_DATA_INDEX_ME_CREF];
ep[VM_ENV_DATA_INDEX_FLAGS] = src_ep[VM_ENV_DATA_INDEX_FLAGS] | VM_ENV_FLAG_ISOLATED;
if (!VM_ENV_LOCAL_P(src_ep)) { if (!VM_ENV_LOCAL_P(src_ep)) {
const VALUE *prev_ep = VM_ENV_PREV_EP(src_env->ep); const VALUE *prev_ep = VM_ENV_PREV_EP(src_env->ep);
const rb_env_t *new_prev_env = env_copy(prev_ep, read_only_variables); const rb_env_t *new_prev_env = env_copy(prev_ep, read_only_variables);
prev_env = (VALUE)new_prev_env; prev_env = (VALUE)new_prev_env;
ep[VM_ENV_DATA_INDEX_SPECVAL] = VM_GUARDED_PREV_EP(new_prev_env->ep); ep[VM_ENV_DATA_INDEX_SPECVAL] = VM_GUARDED_PREV_EP(new_prev_env->ep);
VM_ENV_FLAGS_UNSET(ep, VM_ENV_FLAG_LOCAL);
} }
else { else {
ep[VM_ENV_DATA_INDEX_SPECVAL] = VM_BLOCK_HANDLER_NONE; ep[VM_ENV_DATA_INDEX_SPECVAL] = VM_BLOCK_HANDLER_NONE;
} }
const rb_env_t *copied_env = vm_env_new(ep, env_body, src_env->env_size, src_env->iseq);
RB_GC_GUARD(prev_env); RB_GC_GUARD(prev_env);
return copied_env; return copied_env;
} }