File pthread-mutex-trylock-barrier.patch of Package glibc.33857
2019-02-07 Stefan Liebler <stli@linux.ibm.com>
[BZ #24180]
* nptl/pthread_mutex_trylock.c (__pthread_mutex_trylock):
Add compiler barriers and comments.
Index: glibc-2.26/nptl/pthread_mutex_trylock.c
===================================================================
--- glibc-2.26.orig/nptl/pthread_mutex_trylock.c
+++ glibc-2.26/nptl/pthread_mutex_trylock.c
@@ -92,6 +92,9 @@ __pthread_mutex_trylock (pthread_mutex_t
case PTHREAD_MUTEX_ROBUST_ADAPTIVE_NP:
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
&mutex->__data.__list.__next);
+ /* We need to set op_pending before starting the operation. Also
+ see comments at ENQUEUE_MUTEX. */
+ __asm ("" ::: "memory");
oldval = mutex->__data.__lock;
do
@@ -117,7 +120,12 @@ __pthread_mutex_trylock (pthread_mutex_t
/* But it is inconsistent unless marked otherwise. */
mutex->__data.__owner = PTHREAD_MUTEX_INCONSISTENT;
+ /* We must not enqueue the mutex before we have acquired it.
+ Also see comments at ENQUEUE_MUTEX. */
+ __asm ("" ::: "memory");
ENQUEUE_MUTEX (mutex);
+ /* We need to clear op_pending after we enqueue the mutex. */
+ __asm ("" ::: "memory");
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
/* Note that we deliberately exist here. If we fall
@@ -133,6 +141,8 @@ __pthread_mutex_trylock (pthread_mutex_t
int kind = PTHREAD_MUTEX_TYPE (mutex);
if (kind == PTHREAD_MUTEX_ROBUST_ERRORCHECK_NP)
{
+ /* We do not need to ensure ordering wrt another memory
+ access. Also see comments at ENQUEUE_MUTEX. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
NULL);
return EDEADLK;
@@ -140,6 +150,8 @@ __pthread_mutex_trylock (pthread_mutex_t
if (kind == PTHREAD_MUTEX_ROBUST_RECURSIVE_NP)
{
+ /* We do not need to ensure ordering wrt another memory
+ access. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
NULL);
@@ -158,6 +170,9 @@ __pthread_mutex_trylock (pthread_mutex_t
id, 0);
if (oldval != 0 && (oldval & FUTEX_OWNER_DIED) == 0)
{
+ /* We haven't acquired the lock as it is already acquired by
+ another owner. We do not need to ensure ordering wrt another
+ memory access. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
return EBUSY;
@@ -171,13 +186,20 @@ __pthread_mutex_trylock (pthread_mutex_t
if (oldval == id)
lll_unlock (mutex->__data.__lock,
PTHREAD_ROBUST_MUTEX_PSHARED (mutex));
+ /* FIXME This violates the mutex destruction requirements. See
+ __pthread_mutex_unlock_full. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
return ENOTRECOVERABLE;
}
}
while ((oldval & FUTEX_OWNER_DIED) != 0);
+ /* We must not enqueue the mutex before we have acquired it.
+ Also see comments at ENQUEUE_MUTEX. */
+ __asm ("" ::: "memory");
ENQUEUE_MUTEX (mutex);
+ /* We need to clear op_pending after we enqueue the mutex. */
+ __asm ("" ::: "memory");
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
mutex->__data.__owner = id;
@@ -203,10 +225,15 @@ __pthread_mutex_trylock (pthread_mutex_t
int robust = mutex->__data.__kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP;
if (robust)
- /* Note: robust PI futexes are signaled by setting bit 0. */
- THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
- (void *) (((uintptr_t) &mutex->__data.__list.__next)
- | 1));
+ {
+ /* Note: robust PI futexes are signaled by setting bit 0. */
+ THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
+ (void *) (((uintptr_t) &mutex->__data.__list.__next)
+ | 1));
+ /* We need to set op_pending before starting the operation. Also
+ see comments at ENQUEUE_MUTEX. */
+ __asm ("" ::: "memory");
+ }
oldval = mutex->__data.__lock;
@@ -215,12 +242,16 @@ __pthread_mutex_trylock (pthread_mutex_t
{
if (kind == PTHREAD_MUTEX_ERRORCHECK_NP)
{
+ /* We do not need to ensure ordering wrt another memory
+ access. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
return EDEADLK;
}
if (kind == PTHREAD_MUTEX_RECURSIVE_NP)
{
+ /* We do not need to ensure ordering wrt another memory
+ access. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
/* Just bump the counter. */
@@ -242,6 +273,9 @@ __pthread_mutex_trylock (pthread_mutex_t
{
if ((oldval & FUTEX_OWNER_DIED) == 0)
{
+ /* We haven't acquired the lock as it is already acquired by
+ another owner. We do not need to ensure ordering wrt another
+ memory access. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
return EBUSY;
@@ -262,6 +296,9 @@ __pthread_mutex_trylock (pthread_mutex_t
if (INTERNAL_SYSCALL_ERROR_P (e, __err)
&& INTERNAL_SYSCALL_ERRNO (e, __err) == EWOULDBLOCK)
{
+ /* The kernel has not yet finished the mutex owner death.
+ We do not need to ensure ordering wrt another memory
+ access. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
return EBUSY;
@@ -279,7 +316,12 @@ __pthread_mutex_trylock (pthread_mutex_t
/* But it is inconsistent unless marked otherwise. */
mutex->__data.__owner = PTHREAD_MUTEX_INCONSISTENT;
+ /* We must not enqueue the mutex before we have acquired it.
+ Also see comments at ENQUEUE_MUTEX. */
+ __asm ("" ::: "memory");
ENQUEUE_MUTEX (mutex);
+ /* We need to clear op_pending after we enqueue the mutex. */
+ __asm ("" ::: "memory");
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
/* Note that we deliberately exit here. If we fall
@@ -302,13 +344,20 @@ __pthread_mutex_trylock (pthread_mutex_t
PTHREAD_ROBUST_MUTEX_PSHARED (mutex)),
0, 0);
+ /* To the kernel, this will be visible after the kernel has
+ acquired the mutex in the syscall. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
return ENOTRECOVERABLE;
}
if (robust)
{
+ /* We must not enqueue the mutex before we have acquired it.
+ Also see comments at ENQUEUE_MUTEX. */
+ __asm ("" ::: "memory");
ENQUEUE_MUTEX_PI (mutex);
+ /* We need to clear op_pending after we enqueue the mutex. */
+ __asm ("" ::: "memory");
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
}
