fix data race choosing next key slot in pthread_key_create

commit 84d061d5a31c9c773e29e1e2b1ffe8cb9557bc58 wrongly moved the
access to the global next_key outside of the scope of the lock. the
error manifested as spurious failure to find an available key slot
under concurrent calls to pthread_key_create, since the stopping
condition could be met after only a small number of slots were
examined.

diff --git a/src/thread/pthread_key_create.c b/src/thread/pthread_key_create.c
index 210605c..d112094 100644 (file)
--- a/src/thread/pthread_key_create.c
+++ b/src/thread/pthread_key_create.c
@@ -22,7 +22,6 @@ weak_alias(dummy_0, __tl_unlock);
 
 int __pthread_key_create(pthread_key_t *k, void (*dtor)(void *))
 {
-       pthread_key_t j = next_key;
        pthread_t self = __pthread_self();
 
        /* This can only happen in the main thread before
@@ -33,6 +32,7 @@ int __pthread_key_create(pthread_key_t *k, void (*dtor)(void *))
        if (!dtor) dtor = nodtor;
 
        __pthread_rwlock_wrlock(&key_lock);
+       pthread_key_t j = next_key;
        do {
                if (!keys[j]) {
                        keys[next_key = *k = j] = dtor;