pthread_once: g_lock may lead deadlock

For programs with the dependencies logic in pthread_once callback , using global locks may cause deadlock: task A pthread_once() | |-> nxrmutex_lock(&g_lock); -> init_routine(); // callback to wait task B task B pthread_once() | ->nxrmutex_lock(&g_lock); // Deadlock ->init_routine(); // hold resource to wake up task A Signed-off-by: hujun5 <[email protected]>
hujun260 · Sep 23, 2023 · 6d51443 · 6d51443
1 parent 2bce0f4
commit 6d51443
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Showing 2 changed files with 14 additions and 11 deletions.
diff --git a/include/pthread.h b/include/pthread.h
@@ -136,7 +136,7 @@
 
 /* Used to initialize a pthread_once_t */
 
-#define PTHREAD_ONCE_INIT             (false)
+#define PTHREAD_ONCE_INIT             {false, PTHREAD_MUTEX_INITIALIZER}
 
 /* This is returned by pthread_barrier_wait.  It must not match any errno
  * in errno.h
@@ -371,8 +371,14 @@ typedef struct pthread_barrier_s pthread_barrier_t;
 #  define __PTHREAD_BARRIER_T_DEFINED 1
 #endif
 
+struct pthread_once_s
+{
+  bool done;
+  pthread_mutex_t mutex;
+};
+
 #ifndef __PTHREAD_ONCE_T_DEFINED
-typedef bool pthread_once_t;
+typedef struct pthread_once_s pthread_once_t;
 #  define __PTHREAD_ONCE_T_DEFINED 1
 #endif
 
@@ -839,7 +845,8 @@ typedef FAR struct pthread_spinlock_s pthread_spinlock_t;
 #endif /* CONFIG_PTHREAD_SPINLOCKS */
 
 #ifndef __PTHREAD_ONCE_T_DEFINED
-typedef bool pthread_once_t;
+struct pthread_once_s;
+typedef struct pthread_once_s pthread_once_t;
 #  define __PTHREAD_ONCE_T_DEFINED 1
 #endif
 

diff --git a/libs/libc/pthread/pthread_once.c b/libs/libc/pthread/pthread_once.c
@@ -61,8 +61,6 @@
  *
  ****************************************************************************/
 
-static rmutex_t g_lock = NXRMUTEX_INITIALIZER;
-
 int pthread_once(FAR pthread_once_t *once_control,
                  CODE void (*init_routine)(void))
 {
@@ -75,23 +73,21 @@ int pthread_once(FAR pthread_once_t *once_control,
 
   /* Prohibit pre-emption while we test and set the once_control. */
 
-  nxrmutex_lock(&g_lock);
+  pthread_mutex_lock(&once_control->mutex);
 
-  if (!*once_control)
+  if (!once_control->done)
     {
-      *once_control = true;
+      once_control->done = true;
 
       /* Call the init_routine with pre-emption enabled. */
 
       init_routine();
-      nxrmutex_unlock(&g_lock);
-      return OK;
     }
 
   /* The init_routine has already been called.
    * Restore pre-emption and return.
    */
 
-  nxrmutex_unlock(&g_lock);
+  pthread_mutex_unlock(&once_control->mutex);
   return OK;
 }