}
#endif /* CONFIG_FAIL_FUTEX */
+#ifdef CONFIG_COMPAT
+static void compat_exit_robust_list(struct task_struct *curr);
+#else
+static inline void compat_exit_robust_list(struct task_struct *curr) { }
+#endif
+
static inline void futex_get_mm(union futex_key *key)
{
mmgrab(key->private.mm);
* Kernel cleans up PI-state, but userspace is likely hosed.
* (Robust-futex cleanup is separate and might save the day for userspace.)
*/
-void exit_pi_state_list(struct task_struct *curr)
+static void exit_pi_state_list(struct task_struct *curr)
{
struct list_head *next, *head = &curr->pi_state_list;
struct futex_pi_state *pi_state;
}
raw_spin_unlock_irq(&curr->pi_lock);
}
-
+#else
+static inline void exit_pi_state_list(struct task_struct *curr) { }
#endif
/*
u32 uval2;
/*
- * If PF_EXITPIDONE is not yet set, then try again.
+ * If the futex exit state is not yet FUTEX_STATE_DEAD, wait
+ * for it to finish.
*/
- if (tsk && !(tsk->flags & PF_EXITPIDONE))
+ if (tsk && tsk->futex_state != FUTEX_STATE_DEAD)
return -EAGAIN;
/*
* *uaddr = 0xC0000000; tsk = get_task(PID);
* } if (!tsk->flags & PF_EXITING) {
* ... attach();
- * tsk->flags |= PF_EXITPIDONE; } else {
- * if (!(tsk->flags & PF_EXITPIDONE))
+ * tsk->futex_state = } else {
+ * FUTEX_STATE_DEAD; if (tsk->futex_state !=
+ * FUTEX_STATE_DEAD)
* return -EAGAIN;
* return -ESRCH; <--- FAIL
* }
}
/*
- * We need to look at the task state flags to figure out,
- * whether the task is exiting. To protect against the do_exit
- * change of the task flags, we do this protected by
- * p->pi_lock:
+ * We need to look at the task state to figure out, whether the
+ * task is exiting. To protect against the change of the task state
+ * in futex_exit_release(), we do this protected by p->pi_lock:
*/
raw_spin_lock_irq(&p->pi_lock);
- if (unlikely(p->flags & PF_EXITING)) {
+ if (unlikely(p->futex_state != FUTEX_STATE_OK)) {
/*
- * The task is on the way out. When PF_EXITPIDONE is
- * set, we know that the task has finished the
- * cleanup:
+ * The task is on the way out. When the futex state is
+ * FUTEX_STATE_DEAD, we know that the task has finished
+ * the cleanup:
*/
int ret = handle_exit_race(uaddr, uval, p);
/*
* Queue the task for later wakeup for after we've released
- * the hb->lock. wake_q_add() grabs reference to p.
+ * the hb->lock.
*/
wake_q_add_safe(wake_q, p);
}
return ret;
}
+/* Constants for the pending_op argument of handle_futex_death */
+#define HANDLE_DEATH_PENDING true
+#define HANDLE_DEATH_LIST false
+
/*
* Process a futex-list entry, check whether it's owned by the
* dying task, and do notification if so:
*/
-static int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
+static int handle_futex_death(u32 __user *uaddr, struct task_struct *curr,
+ bool pi, bool pending_op)
{
u32 uval, uninitialized_var(nval), mval;
int err;
if (get_user(uval, uaddr))
return -1;
+ /*
+ * Special case for regular (non PI) futexes. The unlock path in
+ * user space has two race scenarios:
+ *
+ * 1. The unlock path releases the user space futex value and
+ * before it can execute the futex() syscall to wake up
+ * waiters it is killed.
+ *
+ * 2. A woken up waiter is killed before it can acquire the
+ * futex in user space.
+ *
+ * In both cases the TID validation below prevents a wakeup of
+ * potential waiters which can cause these waiters to block
+ * forever.
+ *
+ * In both cases the following conditions are met:
+ *
+ * 1) task->robust_list->list_op_pending != NULL
+ * @pending_op == true
+ * 2) User space futex value == 0
+ * 3) Regular futex: @pi == false
+ *
+ * If these conditions are met, it is safe to attempt waking up a
+ * potential waiter without touching the user space futex value and
+ * trying to set the OWNER_DIED bit. The user space futex value is
+ * uncontended and the rest of the user space mutex state is
+ * consistent, so a woken waiter will just take over the
+ * uncontended futex. Setting the OWNER_DIED bit would create
+ * inconsistent state and malfunction of the user space owner died
+ * handling.
+ */
+ if (pending_op && !pi && !uval) {
+ futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
+ return 0;
+ }
+
if ((uval & FUTEX_TID_MASK) != task_pid_vnr(curr))
return 0;
*
* We silently return on any sign of list-walking problem.
*/
-void exit_robust_list(struct task_struct *curr)
+static void exit_robust_list(struct task_struct *curr)
{
struct robust_list_head __user *head = curr->robust_list;
struct robust_list __user *entry, *next_entry, *pending;
* A pending lock might already be on the list, so
* don't process it twice:
*/
- if (entry != pending)
+ if (entry != pending) {
if (handle_futex_death((void __user *)entry + futex_offset,
- curr, pi))
+ curr, pi, HANDLE_DEATH_LIST))
return;
+ }
if (rc)
return;
entry = next_entry;
cond_resched();
}
- if (pending)
+ if (pending) {
handle_futex_death((void __user *)pending + futex_offset,
- curr, pip);
+ curr, pip, HANDLE_DEATH_PENDING);
+ }
+}
+
+void futex_mm_release(struct task_struct *tsk)
+{
+ if (unlikely(tsk->robust_list)) {
+ exit_robust_list(tsk);
+ tsk->robust_list = NULL;
+ }
+
+#ifdef CONFIG_COMPAT
+ if (unlikely(tsk->compat_robust_list)) {
+ compat_exit_robust_list(tsk);
+ tsk->compat_robust_list = NULL;
+ }
+#endif
+
+ if (unlikely(!list_empty(&tsk->pi_state_list)))
+ exit_pi_state_list(tsk);
}
long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
*
* We silently return on any sign of list-walking problem.
*/
-void compat_exit_robust_list(struct task_struct *curr)
+static void compat_exit_robust_list(struct task_struct *curr)
{
struct compat_robust_list_head __user *head = curr->compat_robust_list;
struct robust_list __user *entry, *next_entry, *pending;
if (entry != pending) {
void __user *uaddr = futex_uaddr(entry, futex_offset);
- if (handle_futex_death(uaddr, curr, pi))
+ if (handle_futex_death(uaddr, curr, pi,
+ HANDLE_DEATH_LIST))
return;
}
if (rc)
if (pending) {
void __user *uaddr = futex_uaddr(pending, futex_offset);
- handle_futex_death(uaddr, curr, pip);
+ handle_futex_death(uaddr, curr, pip, HANDLE_DEATH_PENDING);
}
}
projects / linux.git / blobdiff