Make res_init() thread safe.

res_init() was not atomic, which could give undesired behaviour. Now
res_init() is completely locked under one lock and the locking is
removed from __res_vinit().

Signed-off-by: Kenneth Soerensen <kenneth.sorensen@spectralink.com>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

libc/inet/resolv.c

@@ -3426,6 +3426,7 @@ static void res_sync_func(void)
 	 */
 }
 
+/* has to be called under __resolv_lock */
 static int
 __res_vinit(res_state rp, int preinit)
 {
@@ -3434,7 +3435,6 @@ __res_vinit(res_state rp, int preinit)
 	int m = 0;
 #endif
 
-	__UCLIBC_MUTEX_LOCK(__resolv_lock);
 	__close_nameservers();
 	__open_nameservers();
 
@@ -3526,7 +3526,6 @@ __res_vinit(res_state rp, int preinit)
 
 	rp->options |= RES_INIT;
 
-	__UCLIBC_MUTEX_UNLOCK(__resolv_lock);
 	return 0;
 }
 
@@ -3576,11 +3575,11 @@ res_init(void)
 	if (!_res.id)
 		_res.id = res_randomid();
 
-	__UCLIBC_MUTEX_UNLOCK(__resolv_lock);
-
 	__res_vinit(&_res, 1);
 	__res_sync = res_sync_func;
 
+	__UCLIBC_MUTEX_UNLOCK(__resolv_lock);
+
 	return 0;
 }
 libc_hidden_def(res_init)
@@ -3679,7 +3678,11 @@ struct __res_state *__resp = &_res;
 int
 res_ninit(res_state statp)
 {
-	return __res_vinit(statp, 0);
+	int ret;
+	__UCLIBC_MUTEX_LOCK(__resolv_lock);
+	ret = __res_vinit(statp, 0);
+	__UCLIBC_MUTEX_UNLOCK(__resolv_lock);
+	return ret;
 }
 
 #endif /* L_res_init */