From 9e2d820a555e150df462f88c901fcbe25d692a8b Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Wed, 2 May 2018 12:13:43 -0400 Subject: use a dedicated futex object for pthread_join instead of tid field the tid field in the pthread structure is not volatile, and really shouldn't be, so as not to limit the compiler's ability to reorder, merge, or split loads in code paths that may be relevant to performance (like controlling lock ownership). however, use of objects which are not volatile or atomic with futex wait is inherently broken, since the compiler is free to transform a single load into multiple loads, thereby using a different value for the controlling expression of the loop and the value passed to the futex syscall, leading the syscall to block instead of returning. reportedly glibc's pthread_join was actually affected by an equivalent issue in glibc on s390. add a separate, dedicated join_futex object for pthread_join to use. --- src/env/__init_tls.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'src/env/__init_tls.c') diff --git a/src/env/__init_tls.c b/src/env/__init_tls.c index b125eb1f..80044960 100644 --- a/src/env/__init_tls.c +++ b/src/env/__init_tls.c @@ -15,7 +15,8 @@ int __init_tp(void *p) int r = __set_thread_area(TP_ADJ(p)); if (r < 0) return -1; if (!r) libc.can_do_threads = 1; - td->tid = __syscall(SYS_set_tid_address, &td->tid); + td->join_futex = -1; + td->tid = __syscall(SYS_set_tid_address, &td->join_futex); td->locale = &libc.global_locale; td->robust_list.head = &td->robust_list.head; return 0; -- cgit v1.2.1