On Tue, May 30, 2017 at 03:48:06AM -0400, Ted Unangst wrote:
> talking to stsp, he reminded me of a problematic bug that took some time to
> track down in some desktop software that shall not be named. after a program
> calls fork(), the child has only a single thread. per the standard, it needs
> to get to exec() as quickly as possible. per the quality standards of modern
> software, this doesn't always happen, and then strangeness happens.
>
> this adds a quick check for this error condition. after a fork, we set a new
> variable in the child that we are post threaded. this can be checked elsewhere
> in the library. i added a check to pthread_join because that's a notable
> problem function.
>
>
> Index: rthread.c
> ===================================================================
> RCS file: /cvs/src/lib/librthread/rthread.c,v
> retrieving revision 1.94
> diff -u -p -r1.94 rthread.c
> --- rthread.c 4 Sep 2016 10:13:35 -0000 1.94
> +++ rthread.c 30 May 2017 07:43:12 -0000
> @@ -64,6 +64,7 @@ REDIRECT_SYSCALL(thrkill);
> static int concurrency_level; /* not used */
>
> int _threads_ready;
> +int _post_threaded;
> size_t _thread_pagesize;
> struct listhead _thread_list = LIST_HEAD_INITIALIZER(_thread_list);
> _atomic_lock_t _thread_lock = _SPINLOCK_UNLOCKED;
> @@ -358,6 +359,11 @@ pthread_join(pthread_t thread, void **re
> pthread_t self;
> PREP_CANCEL_POINT(tib);
>
> + if (_post_threaded) {
> +#define GREATSCOTT "great scott! serious repurcussions on future events!\n"
> + write(2, GREATSCOTT, sizeof(GREATSCOTT));
^^^^^^^^^^^^^^^^^^
maybe sizeof(GREATSCOTT)-1
-pk
> + abort();
> + }
> if (!_threads_ready)
> _rthread_init();
> self = tib->tib_thread;
> Index: rthread_fork.c
> ===================================================================
> RCS file: /cvs/src/lib/librthread/rthread_fork.c,v
> retrieving revision 1.19
> diff -u -p -r1.19 rthread_fork.c
> --- rthread_fork.c 4 Sep 2016 10:13:35 -0000 1.19
> +++ rthread_fork.c 30 May 2017 07:41:29 -0000
> @@ -58,6 +58,7 @@ _dofork(pid_t (*sys_fork)(void))
> pthread_t me;
> pid_t newid;
> int i;
> + extern int _post_threaded;
>
> if (!_threads_ready)
> return sys_fork();
> @@ -110,6 +111,7 @@ _dofork(pid_t (*sys_fork)(void))
>
> /* single threaded now */
> __isthreaded = 0;
> + _post_threaded = 1;
> }
> #ifndef NO_PIC
> else if (_DYNAMIC)
>
