ptrace children revamp
[linux-3.10.git] / kernel / exit.c
index 7453356..1e90982 100644 (file)
@@ -71,7 +71,7 @@ static void __unhash_process(struct task_struct *p)
                __get_cpu_var(process_counts)--;
        }
        list_del_rcu(&p->thread_group);
-       remove_parent(p);
+       list_del_init(&p->sibling);
 }
 
 /*
@@ -152,6 +152,18 @@ static void delayed_put_task_struct(struct rcu_head *rhp)
        put_task_struct(container_of(rhp, struct task_struct, rcu));
 }
 
+/*
+ * Do final ptrace-related cleanup of a zombie being reaped.
+ *
+ * Called with write_lock(&tasklist_lock) held.
+ */
+static void ptrace_release_task(struct task_struct *p)
+{
+       BUG_ON(!list_empty(&p->ptraced));
+       ptrace_unlink(p);
+       BUG_ON(!list_empty(&p->ptrace_entry));
+}
+
 void release_task(struct task_struct * p)
 {
        struct task_struct *leader;
@@ -160,8 +172,7 @@ repeat:
        atomic_dec(&p->user->processes);
        proc_flush_task(p);
        write_lock_irq(&tasklist_lock);
-       ptrace_unlink(p);
-       BUG_ON(!list_empty(&p->ptrace_list) || !list_empty(&p->ptrace_children));
+       ptrace_release_task(p);
        __exit_signal(p);
 
        /*
@@ -315,9 +326,8 @@ static void reparent_to_kthreadd(void)
 
        ptrace_unlink(current);
        /* Reparent to init */
-       remove_parent(current);
        current->real_parent = current->parent = kthreadd_task;
-       add_parent(current);
+       list_move_tail(&current->sibling, &current->real_parent->children);
 
        /* Set the exit signal to SIGCHLD so we signal init on exit */
        current->exit_signal = SIGCHLD;
@@ -692,37 +702,71 @@ static void exit_mm(struct task_struct * tsk)
        mmput(mm);
 }
 
-static void
-reparent_thread(struct task_struct *p, struct task_struct *father, int traced)
+/*
+ * Detach all tasks we were using ptrace on.
+ * Any that need to be release_task'd are put on the @dead list.
+ *
+ * Called with write_lock(&tasklist_lock) held.
+ */
+static void ptrace_exit(struct task_struct *parent, struct list_head *dead)
 {
-       if (p->pdeath_signal)
-               /* We already hold the tasklist_lock here.  */
-               group_send_sig_info(p->pdeath_signal, SEND_SIG_NOINFO, p);
+       struct task_struct *p, *n;
 
-       /* Move the child from its dying parent to the new one.  */
-       if (unlikely(traced)) {
-               /* Preserve ptrace links if someone else is tracing this child.  */
-               list_del_init(&p->ptrace_list);
-               if (ptrace_reparented(p))
-                       list_add(&p->ptrace_list, &p->real_parent->ptrace_children);
-       } else {
-               /* If this child is being traced, then we're the one tracing it
-                * anyway, so let go of it.
+       list_for_each_entry_safe(p, n, &parent->ptraced, ptrace_entry) {
+               __ptrace_unlink(p);
+
+               if (p->exit_state != EXIT_ZOMBIE)
+                       continue;
+
+               /*
+                * If it's a zombie, our attachedness prevented normal
+                * parent notification or self-reaping.  Do notification
+                * now if it would have happened earlier.  If it should
+                * reap itself, add it to the @dead list.  We can't call
+                * release_task() here because we already hold tasklist_lock.
+                *
+                * If it's our own child, there is no notification to do.
                 */
-               p->ptrace = 0;
-               remove_parent(p);
-               p->parent = p->real_parent;
-               add_parent(p);
+               if (!task_detached(p) && thread_group_empty(p)) {
+                       if (!same_thread_group(p->real_parent, parent))
+                               do_notify_parent(p, p->exit_signal);
+               }
 
-               if (task_is_traced(p)) {
+               if (task_detached(p)) {
                        /*
-                        * If it was at a trace stop, turn it into
-                        * a normal stop since it's no longer being
-                        * traced.
+                        * Mark it as in the process of being reaped.
                         */
-                       ptrace_untrace(p);
+                       p->exit_state = EXIT_DEAD;
+                       list_add(&p->ptrace_entry, dead);
                }
        }
+}
+
+/*
+ * Finish up exit-time ptrace cleanup.
+ *
+ * Called without locks.
+ */
+static void ptrace_exit_finish(struct task_struct *parent,
+                              struct list_head *dead)
+{
+       struct task_struct *p, *n;
+
+       BUG_ON(!list_empty(&parent->ptraced));
+
+       list_for_each_entry_safe(p, n, dead, ptrace_entry) {
+               list_del_init(&p->ptrace_entry);
+               release_task(p);
+       }
+}
+
+static void reparent_thread(struct task_struct *p, struct task_struct *father)
+{
+       if (p->pdeath_signal)
+               /* We already hold the tasklist_lock here.  */
+               group_send_sig_info(p->pdeath_signal, SEND_SIG_NOINFO, p);
+
+       list_move_tail(&p->sibling, &p->real_parent->children);
 
        /* If this is a threaded reparent there is no need to
         * notify anyone anything has happened.
@@ -737,7 +781,8 @@ reparent_thread(struct task_struct *p, struct task_struct *father, int traced)
        /* If we'd notified the old parent about this child's death,
         * also notify the new parent.
         */
-       if (!traced && p->exit_state == EXIT_ZOMBIE &&
+       if (!ptrace_reparented(p) &&
+           p->exit_state == EXIT_ZOMBIE &&
            !task_detached(p) && thread_group_empty(p))
                do_notify_parent(p, p->exit_signal);
 
@@ -754,12 +799,15 @@ reparent_thread(struct task_struct *p, struct task_struct *father, int traced)
 static void forget_original_parent(struct task_struct *father)
 {
        struct task_struct *p, *n, *reaper = father;
-       struct list_head ptrace_dead;
-
-       INIT_LIST_HEAD(&ptrace_dead);
+       LIST_HEAD(ptrace_dead);
 
        write_lock_irq(&tasklist_lock);
 
+       /*
+        * First clean up ptrace if we were using it.
+        */
+       ptrace_exit(father, &ptrace_dead);
+
        do {
                reaper = next_thread(reaper);
                if (reaper == father) {
@@ -768,58 +816,19 @@ static void forget_original_parent(struct task_struct *father)
                }
        } while (reaper->flags & PF_EXITING);
 
-       /*
-        * There are only two places where our children can be:
-        *
-        * - in our child list
-        * - in our ptraced child list
-        *
-        * Search them and reparent children.
-        */
        list_for_each_entry_safe(p, n, &father->children, sibling) {
-               int ptrace;
-
-               ptrace = p->ptrace;
-
-               /* if father isn't the real parent, then ptrace must be enabled */
-               BUG_ON(father != p->real_parent && !ptrace);
-
-               if (father == p->real_parent) {
-                       /* reparent with a reaper, real father it's us */
-                       p->real_parent = reaper;
-                       reparent_thread(p, father, 0);
-               } else {
-                       /* reparent ptraced task to its real parent */
-                       __ptrace_unlink (p);
-                       if (p->exit_state == EXIT_ZOMBIE && !task_detached(p) &&
-                           thread_group_empty(p))
-                               do_notify_parent(p, p->exit_signal);
-               }
-
-               /*
-                * if the ptraced child is a detached zombie we must collect
-                * it before we exit, or it will remain zombie forever since
-                * we prevented it from self-reap itself while it was being
-                * traced by us, to be able to see it in wait4.
-                */
-               if (unlikely(ptrace && p->exit_state == EXIT_ZOMBIE && task_detached(p)))
-                       list_add(&p->ptrace_list, &ptrace_dead);
-       }
-
-       list_for_each_entry_safe(p, n, &father->ptrace_children, ptrace_list) {
                p->real_parent = reaper;
-               reparent_thread(p, father, 1);
+               if (p->parent == father) {
+                       BUG_ON(p->ptrace);
+                       p->parent = p->real_parent;
+               }
+               reparent_thread(p, father);
        }
 
        write_unlock_irq(&tasklist_lock);
        BUG_ON(!list_empty(&father->children));
-       BUG_ON(!list_empty(&father->ptrace_children));
-
-       list_for_each_entry_safe(p, n, &ptrace_dead, ptrace_list) {
-               list_del_init(&p->ptrace_list);
-               release_task(p);
-       }
 
+       ptrace_exit_finish(father, &ptrace_dead);
 }
 
 /*
@@ -1180,13 +1189,6 @@ static int eligible_child(enum pid_type type, struct pid *pid, int options,
                        return 0;
        }
 
-       /*
-        * Do not consider detached threads that are
-        * not ptraced:
-        */
-       if (task_detached(p) && !p->ptrace)
-               return 0;
-
        /* Wait for all children (clone and not) if __WALL is set;
         * otherwise, wait for clone children *only* if __WCLONE is
         * set; otherwise, wait for non-clone children *only*.  (Note:
@@ -1399,7 +1401,7 @@ static int wait_task_zombie(struct task_struct *p, int options,
  * the lock and this task is uninteresting.  If we return nonzero, we have
  * released the lock and the system call should return.
  */
-static int wait_task_stopped(struct task_struct *p,
+static int wait_task_stopped(int ptrace, struct task_struct *p,
                             int options, struct siginfo __user *infop,
                             int __user *stat_addr, struct rusage __user *ru)
 {
@@ -1407,7 +1409,7 @@ static int wait_task_stopped(struct task_struct *p,
        uid_t uid = 0; /* unneeded, required by compiler */
        pid_t pid;
 
-       if (!(p->ptrace & PT_PTRACED) && !(options & WUNTRACED))
+       if (!(options & WUNTRACED))
                return 0;
 
        exit_code = 0;
@@ -1416,7 +1418,7 @@ static int wait_task_stopped(struct task_struct *p,
        if (unlikely(!task_is_stopped_or_traced(p)))
                goto unlock_sig;
 
-       if (!(p->ptrace & PT_PTRACED) && p->signal->group_stop_count > 0)
+       if (!ptrace && p->signal->group_stop_count > 0)
                /*
                 * A group stop is in progress and this is the group leader.
                 * We won't report until all threads have stopped.
@@ -1445,7 +1447,7 @@ unlock_sig:
         */
        get_task_struct(p);
        pid = task_pid_vnr(p);
-       why = (p->ptrace & PT_PTRACED) ? CLD_TRAPPED : CLD_STOPPED;
+       why = ptrace ? CLD_TRAPPED : CLD_STOPPED;
        read_unlock(&tasklist_lock);
 
        if (unlikely(options & WNOWAIT))
@@ -1536,7 +1538,7 @@ static int wait_task_continued(struct task_struct *p, int options,
  * Returns zero if the search for a child should continue;
  * then *@notask_error is 0 if @p is an eligible child, or still -ECHILD.
  */
-static int wait_consider_task(struct task_struct *parent,
+static int wait_consider_task(struct task_struct *parent, int ptrace,
                              struct task_struct *p, int *notask_error,
                              enum pid_type type, struct pid *pid, int options,
                              struct siginfo __user *infop,
@@ -1546,6 +1548,15 @@ static int wait_consider_task(struct task_struct *parent,
        if (ret <= 0)
                return ret;
 
+       if (likely(!ptrace) && unlikely(p->ptrace)) {
+               /*
+                * This child is hidden by ptrace.
+                * We aren't allowed to see it now, but eventually we will.
+                */
+               *notask_error = 0;
+               return 0;
+       }
+
        if (p->exit_state == EXIT_DEAD)
                return 0;
 
@@ -1562,7 +1573,8 @@ static int wait_consider_task(struct task_struct *parent,
        *notask_error = 0;
 
        if (task_is_stopped_or_traced(p))
-               return wait_task_stopped(p, options, infop, stat_addr, ru);
+               return wait_task_stopped(ptrace, p, options,
+                                        infop, stat_addr, ru);
 
        return wait_task_continued(p, options, infop, stat_addr, ru);
 }
@@ -1583,11 +1595,16 @@ static int do_wait_thread(struct task_struct *tsk, int *notask_error,
        struct task_struct *p;
 
        list_for_each_entry(p, &tsk->children, sibling) {
-               int ret = wait_consider_task(tsk, p, notask_error,
-                                            type, pid, options,
-                                            infop, stat_addr, ru);
-               if (ret)
-                       return ret;
+               /*
+                * Do not consider detached threads.
+                */
+               if (!task_detached(p)) {
+                       int ret = wait_consider_task(tsk, 0, p, notask_error,
+                                                    type, pid, options,
+                                                    infop, stat_addr, ru);
+                       if (ret)
+                               return ret;
+               }
        }
 
        return 0;
@@ -1601,21 +1618,16 @@ static int ptrace_do_wait(struct task_struct *tsk, int *notask_error,
        struct task_struct *p;
 
        /*
-        * If we never saw an eligile child, check for children stolen by
-        * ptrace.  We don't leave -ECHILD in *@notask_error if there are any,
-        * because we will eventually be allowed to wait for them again.
+        * Traditionally we see ptrace'd stopped tasks regardless of options.
         */
-       if (!*notask_error)
-               return 0;
+       options |= WUNTRACED;
 
-       list_for_each_entry(p, &tsk->ptrace_children, ptrace_list) {
-               int ret = eligible_child(type, pid, options, p);
-               if (unlikely(ret < 0))
+       list_for_each_entry(p, &tsk->ptraced, ptrace_entry) {
+               int ret = wait_consider_task(tsk, 1, p, notask_error,
+                                            type, pid, options,
+                                            infop, stat_addr, ru);
+               if (ret)
                        return ret;
-               if (ret) {
-                       *notask_error = 0;
-                       return 0;
-               }
        }
 
        return 0;