fix serious bug in pthread_join

on spurious wakeups/returns from __timedwait, pthread_join would
"succeed" and unmap the thread's stack while it was still running. at
best this would lead to SIGSEGV when the thread resumed execution, but
in the worst case, the thread would later resume executing on top of
another new thread's stack mapped at the same address.

spent about 4 hours tracking this bug down, chasing rare
difficult-to-reproduce stack corruption in a stress test program.
still no idea *what* caused the spurious wakeups; i suspect it's a
kernel bug.

diff --git a/src/thread/pthread_join.c b/src/thread/pthread_join.c
index 1b0c4f3..86191f2 100644 (file)
--- a/src/thread/pthread_join.c
+++ b/src/thread/pthread_join.c
@@ -6,8 +6,8 @@ static void dummy(void *p)
 
 int pthread_join(pthread_t t, void **res)
 {
 
 int pthread_join(pthread_t t, void **res)
 {

-       int tmp = t->tid;
-       if (tmp) __timedwait(&t->tid, tmp, 0, 0, dummy, 0, 0);
+       int tmp;
+       while ((tmp = t->tid)) __timedwait(&t->tid, tmp, 0, 0, dummy, 0, 0);

        if (res) *res = t->result;
        if (t->map_base) munmap(t->map_base, t->map_size);
        return 0;
        if (res) *res = t->result;
        if (t->map_base) munmap(t->map_base, t->map_size);
        return 0;