fix extremely rare but dangerous race condition in robust mutexes

[musl] / src / thread / pthread_barrier_wait.c

diff --git a/src/thread/pthread_barrier_wait.c b/src/thread/pthread_barrier_wait.c
index 71f7b5f..5e60338 100644 (file)
--- a/src/thread/pthread_barrier_wait.c
+++ b/src/thread/pthread_barrier_wait.c
@@ -1,22 +1,7 @@
 #include "pthread_impl.h"
 
-static int vmlock[2];
-
-void __vm_lock(int inc)
-{
-       for (;;) {
-               int v = vmlock[0];
-               if (inc*v < 0) __wait(vmlock, vmlock+1, v, 1);
-               else if (a_cas(vmlock, v, v+inc)==v) break;
-       }
-}
-
-void __vm_unlock(void)
-{
-       if (vmlock[0]>0) a_dec(vmlock);
-       else a_inc(vmlock);
-       if (vmlock[1]) __wake(vmlock, 1, 1);
-}
+void __vm_lock_impl(int);
+void __vm_unlock_impl(void);
 
 static int pshared_barrier_wait(pthread_barrier_t *b)
 {
@@ -41,7 +26,7 @@ static int pshared_barrier_wait(pthread_barrier_t *b)
                        __wait(&b->_b_count, &b->_b_waiters2, v, 0);
        }
 
-       __vm_lock(+1);
+       __vm_lock_impl(+1);
 
        /* Ensure all threads have a vm lock before proceeding */
        if (a_fetch_add(&b->_b_count, -1)==1-limit) {
@@ -62,7 +47,7 @@ static int pshared_barrier_wait(pthread_barrier_t *b)
        if (v==INT_MIN+1 || (v==1 && w))
                __wake(&b->_b_lock, 1, 0);
 
-       __vm_unlock();
+       __vm_unlock_impl();
 
        return ret;
 }