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pthread_once: g_lock may lead deadlock

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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 <hujun5@xiaomi.com>
This commit is contained in:
hujun5 2023-09-21 17:36:27 +08:00 committed by Xiang Xiao
parent f02ad03124
commit b6693065e7
2 changed files with 20 additions and 20 deletions
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13
include/pthread.h
View File

@ -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

27
libs/libc/pthread/pthread_once.c
View File

@ -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))
{
@ -73,25 +71,20 @@ int pthread_once(FAR pthread_once_t *once_control,
return EINVAL;
}
/* Prohibit pre-emption while we test and set the once_control. */
nxrmutex_lock(&g_lock);
if (!*once_control)
if (!once_control->done)
{
*once_control = true;
pthread_mutex_lock(&once_control->mutex);
/* Call the init_routine with pre-emption enabled. */
if (!once_control->done)
{
/* Call the init_routine with pre-emption enabled. */
init_routine();
nxrmutex_unlock(&g_lock);
return OK;
init_routine();
once_control->done = true;
}
pthread_mutex_unlock(&once_control->mutex);
}
/* The init_routine has already been called.
* Restore pre-emption and return.
*/
nxrmutex_unlock(&g_lock);
return OK;
}