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ecl_import_current_thread: fix segmentation fault

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Bug was introduced by the recent race condition fixes of commit
cc7c0d4386. ecl_list_process needs to be
able to allocate memory and bind special variables, which wasn't possible
previously, because the environment was not yet initialized. Since we can't
initialize the environment before calling ecl_list_process (that was the
reason for the race condition in the first place), we use the fake environment
allocated on the stack (where the gc can find its contents) until we can
safely call ecl_list_process and switch over to the real environment.

Fixes #564.
This commit is contained in:
Marius Gerbershagen 2020-02-29 20:02:36 +01:00
parent 0577802718
commit a7e694de0e
1 changed files with 19 additions and 16 deletions
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35
src/c/threads/process.d
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@ -391,30 +391,33 @@ ecl_import_current_thread(cl_object name, cl_object bindings)
return 0;
}
}
/* We need a fake env to allow for interrupts blocking. */
/* We need a fake env to allow for interrupts blocking and to set up
* frame stacks or other stuff which may be needed by alloc_process
* and ecl_list_process. Since the fake env is allocated on the stack,
* we can safely store pointers to memory allocated by the gc there. */
memset(env_aux, 0, sizeof(*env_aux));
env_aux->disable_interrupts = 1;
ecl_set_process_env(env_aux);
env = _ecl_alloc_env(0);
ecl_set_process_env(env);
ecl_init_env(env_aux);
/* Link environment and process together */
env->own_process = process = alloc_process(name, bindings);
/* Allocate real environment, link it together with process */
env = _ecl_alloc_env(0);
process = alloc_process(name, bindings);
process->process.env = env;
process->process.phase = ECL_PROCESS_BOOTING;
process->process.thread = current;
/* Immediately list the process such that its environment is
* marked by the gc when its contents are allocated */
/* Copy initial bindings from process to the fake environment */
env_aux->cleanup = registered;
env_aux->bindings_array = process->process.initial_bindings;
env_aux->thread_local_bindings_size = env_aux->bindings_array->vector.dim;
env_aux->thread_local_bindings = env_aux->bindings_array->vector.self.t;
/* Switch over to the real environment */
memcpy(env, env_aux, sizeof(*env));
env->own_process = process;
ecl_set_process_env(env);
ecl_list_process(process);
/* Now we can safely allocate memory for the environment contents
* and store pointers to it in the environment */
ecl_init_env(env);
env->cleanup = registered;
env->bindings_array = process->process.initial_bindings;
env->thread_local_bindings_size = env->bindings_array->vector.dim;
env->thread_local_bindings = env->bindings_array->vector.self.t;
ecl_enable_interrupts_env(env);
/* Activate the barrier so that processes can immediately start waiting. */