diff options
Diffstat (limited to 'nptl/descr.h')
| -rw-r--r-- | nptl/descr.h | 21 |
1 files changed, 20 insertions, 1 deletions
diff --git a/nptl/descr.h b/nptl/descr.h index 7a6a94fe15..a145860f07 100644 --- a/nptl/descr.h +++ b/nptl/descr.h @@ -179,7 +179,16 @@ struct pthread but the pointer to the next/previous element of the list points in the middle of the object, the __next element. Whenever casting to __pthread_list_t we need to adjust the pointer - first. */ + first. + These operations are effectively concurrent code in that the thread + can get killed at any point in time and the kernel takes over. Thus, + the __next elements are a kind of concurrent list and we need to + enforce using compiler barriers that the individual operations happen + in such a way that the kernel always sees a consistent list. The + backward links (ie, the __prev elements) are not used by the kernel. + FIXME We should use relaxed MO atomic operations here and signal fences + because this kind of concurrency is similar to synchronizing with a + signal handler. */ # define QUEUE_PTR_ADJUST (offsetof (__pthread_list_t, __next)) # define ENQUEUE_MUTEX_BOTH(mutex, val) \ @@ -191,6 +200,8 @@ struct pthread mutex->__data.__list.__next = THREAD_GETMEM (THREAD_SELF, \ robust_head.list); \ mutex->__data.__list.__prev = (void *) &THREAD_SELF->robust_head; \ + /* Ensure that the new list entry is ready before we insert it. */ \ + __asm ("" ::: "memory"); \ THREAD_SETMEM (THREAD_SELF, robust_head.list, \ (void *) (((uintptr_t) &mutex->__data.__list.__next) \ | val)); \ @@ -205,6 +216,9 @@ struct pthread ((char *) (((uintptr_t) mutex->__data.__list.__prev) & ~1ul) \ - QUEUE_PTR_ADJUST); \ prev->__next = mutex->__data.__list.__next; \ + /* Ensure that we remove the entry from the list before we change the \ + __next pointer of the entry, which is read by the kernel. */ \ + __asm ("" ::: "memory"); \ mutex->__data.__list.__prev = NULL; \ mutex->__data.__list.__next = NULL; \ } while (0) @@ -219,6 +233,8 @@ struct pthread do { \ mutex->__data.__list.__next \ = THREAD_GETMEM (THREAD_SELF, robust_list.__next); \ + /* Ensure that the new list entry is ready before we insert it. */ \ + __asm ("" ::: "memory"); \ THREAD_SETMEM (THREAD_SELF, robust_list.__next, \ (void *) (((uintptr_t) &mutex->__data.__list) | val)); \ } while (0) @@ -239,6 +255,9 @@ struct pthread } \ \ runp->__next = next->__next; \ + /* Ensure that we remove the entry from the list before we change the \ + __next pointer of the entry, which is read by the kernel. */ \ + __asm ("" ::: "memory"); \ mutex->__data.__list.__next = NULL; \ } \ } while (0) |