fix signal masking race in pthread_create with priority attributes
if the parent thread was able to set the new thread's priority before
it reached the check for 'startlock', the new thread failed to restore
its signal mask and thus ran with all signals blocked.
concept for patch by Sergei, who reported the issue; unnecessary
changes were removed and comments added since the whole 'startlock'
thing is non-idiomatic and confusing. eventually it should be replaced
with use of idiomatic synchronization primitives.
diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c
index 49f2f72..6cbf85b 100644
--- a/src/thread/pthread_create.c
+++ b/src/thread/pthread_create.c
@@ -131,9 +131,14 @@
static int start(void *p)
{
pthread_t self = p;
+ /* States for startlock:
+ * 0 = no need for start sync
+ * 1 = waiting for parent to do work
+ * 2 = failure in parent, child must abort
+ * 3 = success in parent, child must restore sigmask */
if (self->startlock[0]) {
__wait(self->startlock, 0, 1, 1);
- if (self->startlock[0]) {
+ if (self->startlock[0] == 2) {
self->detached = 2;
pthread_exit(0);
}
@@ -295,7 +300,7 @@
if (do_sched) {
ret = __syscall(SYS_sched_setscheduler, new->tid,
attr._a_policy, &attr._a_prio);
- a_store(new->startlock, ret<0 ? 2 : 0);
+ a_store(new->startlock, ret<0 ? 2 : 3);
__wake(new->startlock, 1, 1);
if (ret < 0) return -ret;
}