Merge branch 'ptrace-cleanup' of git://git.kernel.org/pub/scm/linux/kernel/git/frob/linux-2.6-utrace

* 'ptrace-cleanup' of git://git.kernel.org/pub/scm/linux/kernel/git/frob/linux-2.6-utrace:
  fix dangling zombie when new parent ignores children
  do_wait: return security_task_wait() error code in place of -ECHILD
  ptrace children revamp
  do_wait reorganization

5 files changed, 318 insertions, 206 deletions

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 9927a88674a3..93c45acf249a 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -140,8 +140,8 @@ extern struct group_info init_groups;
                 .nr_cpus_allowed = NR_CPUS,                             \
         },                                                              \
         .tasks          = LIST_HEAD_INIT(tsk.tasks),                    \
-        .ptrace_children= LIST_HEAD_INIT(tsk.ptrace_children),          \
-        .ptrace_list    = LIST_HEAD_INIT(tsk.ptrace_list),              \
+        .ptraced        = LIST_HEAD_INIT(tsk.ptraced),                  \
+        .ptrace_entry   = LIST_HEAD_INIT(tsk.ptrace_entry),             \
         .real_parent    = &tsk,                                         \
         .parent         = &tsk,                                         \
         .children       = LIST_HEAD_INIT(tsk.children),                 \
diff --git a/include/linux/sched.h b/include/linux/sched.h
index ba2f859c6e4f..1941d8b5cf11 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1062,12 +1062,6 @@ struct task_struct {
 #endif
 
         struct list_head tasks;
-        /*
-         * ptrace_list/ptrace_children forms the list of my children
-         * that were stolen by a ptracer.
-         */
-        struct list_head ptrace_children;
-        struct list_head ptrace_list;
 
         struct mm_struct *mm, *active_mm;
 
@@ -1089,18 +1083,25 @@ struct task_struct {
         /* 
          * pointers to (original) parent process, youngest child, younger sibling,
          * older sibling, respectively.  (p->father can be replaced with 
-         * p->parent->pid)
+         * p->real_parent->pid)
          */
-        struct task_struct *real_parent; /* real parent process (when being debugged) */
-        struct task_struct *parent;     /* parent process */
+        struct task_struct *real_parent; /* real parent process */
+        struct task_struct *parent; /* recipient of SIGCHLD, wait4() reports */
         /*
-         * children/sibling forms the list of my children plus the
-         * tasks I'm ptracing.
+         * children/sibling forms the list of my natural children
          */
         struct list_head children;      /* list of my children */
         struct list_head sibling;       /* linkage in my parent's children list */
         struct task_struct *group_leader;       /* threadgroup leader */
 
+        /*
+         * ptraced is the list of tasks this task is using ptrace on.
+         * This includes both natural children and PTRACE_ATTACH targets.
+         * p->ptrace_entry is p's link on the p->parent->ptraced list.
+         */
+        struct list_head ptraced;
+        struct list_head ptrace_entry;
+
         /* PID/PID hash table linkage. */
         struct pid_link pids[PIDTYPE_MAX];
         struct list_head thread_group;
@@ -1876,9 +1877,6 @@ extern void wait_task_inactive(struct task_struct * p);
 #define wait_task_inactive(p)   do { } while (0)
 #endif
 
-#define remove_parent(p)        list_del_init(&(p)->sibling)
-#define add_parent(p)           list_add_tail(&(p)->sibling,&(p)->parent->children)
-
 #define next_task(p)    list_entry(rcu_dereference((p)->tasks.next), struct task_struct, tasks)
 
 #define for_each_process(p) \
diff --git a/kernel/exit.c b/kernel/exit.c
index ceb258782835..93d2711b9381 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -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 +702,97 @@ static void exit_mm(struct task_struct * tsk)
         mmput(mm);
 }
 
-static void
-reparent_thread(struct task_struct *p, struct task_struct *father, int traced)
+/*
+ * Return nonzero if @parent's children should reap themselves.
+ *
+ * Called with write_lock_irq(&tasklist_lock) held.
+ */
+static int ignoring_children(struct task_struct *parent)
 {
-        if (p->pdeath_signal)
-                /* We already hold the tasklist_lock here.  */
-                group_send_sig_info(p->pdeath_signal, SEND_SIG_NOINFO, p);
+        int ret;
+        struct sighand_struct *psig = parent->sighand;
+        unsigned long flags;
+        spin_lock_irqsave(&psig->siglock, flags);
+        ret = (psig->action[SIGCHLD-1].sa.sa_handler == SIG_IGN ||
+               (psig->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDWAIT));
+        spin_unlock_irqrestore(&psig->siglock, flags);
+        return ret;
+}
 
-        /* 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.
+/*
+ * 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)
+{
+        struct task_struct *p, *n;
+        int ign = -1;
+
+        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.
+                 * But if our normal children self-reap, then this child
+                 * was prevented by ptrace and we must reap it now.
                  */
-                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);
+                        else {
+                                if (ign < 0)
+                                        ign = ignoring_children(parent);
+                                if (ign)
+                                        p->exit_signal = -1;
+                        }
+                }
 
-                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 +807,8 @@ 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 +825,15 @@ 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 +842,19 @@ 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 +1215,6 @@ 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:
@@ -1197,14 +1225,10 @@ static int eligible_child(enum pid_type type, struct pid *pid, int options,
                 return 0;
 
         err = security_task_wait(p);
-        if (likely(!err))
-                return 1;
+        if (err)
+                return err;
 
-        if (type != PIDTYPE_PID)
-                return 0;
-        /* This child was explicitly requested, abort */
-        read_unlock(&tasklist_lock);
-        return err;
+        return 1;
 }
 
 static int wait_noreap_copyout(struct task_struct *p, pid_t pid, uid_t uid,
@@ -1238,7 +1262,7 @@ static int wait_noreap_copyout(struct task_struct *p, pid_t pid, uid_t uid,
  * 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_zombie(struct task_struct *p, int noreap,
+static int wait_task_zombie(struct task_struct *p, int options,
                             struct siginfo __user *infop,
                             int __user *stat_addr, struct rusage __user *ru)
 {
@@ -1246,7 +1270,10 @@ static int wait_task_zombie(struct task_struct *p, int noreap,
         int retval, status, traced;
         pid_t pid = task_pid_vnr(p);
 
-        if (unlikely(noreap)) {
+        if (!likely(options & WEXITED))
+                return 0;
+
+        if (unlikely(options & WNOWAIT)) {
                 uid_t uid = p->uid;
                 int exit_code = p->exit_code;
                 int why, status;
@@ -1396,21 +1423,24 @@ static int wait_task_zombie(struct task_struct *p, int noreap,
  * 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,
-                             int noreap, struct siginfo __user *infop,
+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)
 {
         int retval, exit_code, why;
         uid_t uid = 0; /* unneeded, required by compiler */
         pid_t pid;
 
+        if (!(options & WUNTRACED))
+                return 0;
+
         exit_code = 0;
         spin_lock_irq(&p->sighand->siglock);
 
         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.
@@ -1421,7 +1451,7 @@ static int wait_task_stopped(struct task_struct *p,
         if (!exit_code)
                 goto unlock_sig;
 
-        if (!noreap)
+        if (!unlikely(options & WNOWAIT))
                 p->exit_code = 0;
 
         uid = p->uid;
@@ -1439,10 +1469,10 @@ 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(noreap))
+        if (unlikely(options & WNOWAIT))
                 return wait_noreap_copyout(p, pid, uid,
                                            why, exit_code,
                                            infop, ru);
@@ -1476,7 +1506,7 @@ unlock_sig:
  * 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_continued(struct task_struct *p, int noreap,
+static int wait_task_continued(struct task_struct *p, int options,
                                struct siginfo __user *infop,
                                int __user *stat_addr, struct rusage __user *ru)
 {
@@ -1484,6 +1514,9 @@ static int wait_task_continued(struct task_struct *p, int noreap,
         pid_t pid;
         uid_t uid;
 
+        if (!unlikely(options & WCONTINUED))
+                return 0;
+
         if (!(p->signal->flags & SIGNAL_STOP_CONTINUED))
                 return 0;
 
@@ -1493,7 +1526,7 @@ static int wait_task_continued(struct task_struct *p, int noreap,
                 spin_unlock_irq(&p->sighand->siglock);
                 return 0;
         }
-        if (!noreap)
+        if (!unlikely(options & WNOWAIT))
                 p->signal->flags &= ~SIGNAL_STOP_CONTINUED;
         spin_unlock_irq(&p->sighand->siglock);
 
@@ -1519,89 +1552,161 @@ static int wait_task_continued(struct task_struct *p, int noreap,
         return retval;
 }
 
+/*
+ * Consider @p for a wait by @parent.
+ *
+ * -ECHILD should be in *@notask_error before the first call.
+ * Returns nonzero for a final return, when we have unlocked tasklist_lock.
+ * Returns zero if the search for a child should continue;
+ * then *@notask_error is 0 if @p is an eligible child,
+ * or another error from security_task_wait(), or still -ECHILD.
+ */
+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,
+                              int __user *stat_addr, struct rusage __user *ru)
+{
+        int ret = eligible_child(type, pid, options, p);
+        if (!ret)
+                return ret;
+
+        if (unlikely(ret < 0)) {
+                /*
+                 * If we have not yet seen any eligible child,
+                 * then let this error code replace -ECHILD.
+                 * A permission error will give the user a clue
+                 * to look for security policy problems, rather
+                 * than for mysterious wait bugs.
+                 */
+                if (*notask_error)
+                        *notask_error = 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;
+
+        /*
+         * We don't reap group leaders with subthreads.
+         */
+        if (p->exit_state == EXIT_ZOMBIE && !delay_group_leader(p))
+                return wait_task_zombie(p, options, infop, stat_addr, ru);
+
+        /*
+         * It's stopped or running now, so it might
+         * later continue, exit, or stop again.
+         */
+        *notask_error = 0;
+
+        if (task_is_stopped_or_traced(p))
+                return wait_task_stopped(ptrace, p, options,
+                                         infop, stat_addr, ru);
+
+        return wait_task_continued(p, options, infop, stat_addr, ru);
+}
+
+/*
+ * Do the work of do_wait() for one thread in the group, @tsk.
+ *
+ * -ECHILD should be in *@notask_error before the first call.
+ * Returns nonzero for a final return, when we have unlocked tasklist_lock.
+ * Returns zero if the search for a child should continue; then
+ * *@notask_error is 0 if there were any eligible children,
+ * or another error from security_task_wait(), or still -ECHILD.
+ */
+static int do_wait_thread(struct task_struct *tsk, int *notask_error,
+                          enum pid_type type, struct pid *pid, int options,
+                          struct siginfo __user *infop, int __user *stat_addr,
+                          struct rusage __user *ru)
+{
+        struct task_struct *p;
+
+        list_for_each_entry(p, &tsk->children, sibling) {
+                /*
+                 * 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;
+}
+
+static int ptrace_do_wait(struct task_struct *tsk, int *notask_error,
+                          enum pid_type type, struct pid *pid, int options,
+                          struct siginfo __user *infop, int __user *stat_addr,
+                          struct rusage __user *ru)
+{
+        struct task_struct *p;
+
+        /*
+         * Traditionally we see ptrace'd stopped tasks regardless of options.
+         */
+        options |= WUNTRACED;
+
+        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;
+        }
+
+        return 0;
+}
+
 static long do_wait(enum pid_type type, struct pid *pid, int options,
                     struct siginfo __user *infop, int __user *stat_addr,
                     struct rusage __user *ru)
 {
         DECLARE_WAITQUEUE(wait, current);
         struct task_struct *tsk;
-        int flag, retval;
+        int retval;
 
         add_wait_queue(&current->signal->wait_chldexit,&wait);
 repeat:
-        /* If there is nothing that can match our critier just get out */
+        /*
+         * If there is nothing that can match our critiera just get out.
+         * We will clear @retval to zero if we see any child that might later
+         * match our criteria, even if we are not able to reap it yet.
+         */
         retval = -ECHILD;
         if ((type < PIDTYPE_MAX) && (!pid || hlist_empty(&pid->tasks[type])))
                 goto end;
 
-        /*
-         * We will set this flag if we see any child that might later
-         * match our criteria, even if we are not able to reap it yet.
-         */
-        flag = retval = 0;
         current->state = TASK_INTERRUPTIBLE;
         read_lock(&tasklist_lock);
         tsk = current;
         do {
-                struct task_struct *p;
-
-                list_for_each_entry(p, &tsk->children, sibling) {
-                        int ret = eligible_child(type, pid, options, p);
-                        if (!ret)
-                                continue;
-
-                        if (unlikely(ret < 0)) {
-                                retval = ret;
-                        } else if (task_is_stopped_or_traced(p)) {
-                                /*
-                                 * It's stopped now, so it might later
-                                 * continue, exit, or stop again.
-                                 */
-                                flag = 1;
-                                if (!(p->ptrace & PT_PTRACED) &&
-                                    !(options & WUNTRACED))
-                                        continue;
-
-                                retval = wait_task_stopped(p,
-                                                (options & WNOWAIT), infop,
-                                                stat_addr, ru);
-                        } else if (p->exit_state == EXIT_ZOMBIE &&
-                                        !delay_group_leader(p)) {
-                                /*
-                                 * We don't reap group leaders with subthreads.
-                                 */
-                                if (!likely(options & WEXITED))
-                                        continue;
-                                retval = wait_task_zombie(p,
-                                                (options & WNOWAIT), infop,
-                                                stat_addr, ru);
-                        } else if (p->exit_state != EXIT_DEAD) {
-                                /*
-                                 * It's running now, so it might later
-                                 * exit, stop, or stop and then continue.
-                                 */
-                                flag = 1;
-                                if (!unlikely(options & WCONTINUED))
-                                        continue;
-                                retval = wait_task_continued(p,
-                                                (options & WNOWAIT), infop,
-                                                stat_addr, ru);
-                        }
-                        if (retval != 0) /* tasklist_lock released */
-                                goto end;
-                }
-                if (!flag) {
-                        list_for_each_entry(p, &tsk->ptrace_children,
-                                                                ptrace_list) {
-                                flag = eligible_child(type, pid, options, p);
-                                if (!flag)
-                                        continue;
-                                if (likely(flag > 0))
-                                        break;
-                                retval = flag;
-                                goto end;
-                        }
+                int tsk_result = do_wait_thread(tsk, &retval,
+                                                type, pid, options,
+                                                infop, stat_addr, ru);
+                if (!tsk_result)
+                        tsk_result = ptrace_do_wait(tsk, &retval,
+                                                    type, pid, options,
+                                                    infop, stat_addr, ru);
+                if (tsk_result) {
+                        /*
+                         * tasklist_lock is unlocked and we have a final result.
+                         */
+                        retval = tsk_result;
+                        goto end;
                 }
+
                 if (options & __WNOTHREAD)
                         break;
                 tsk = next_thread(tsk);
@@ -1609,16 +1714,14 @@ repeat:
         } while (tsk != current);
         read_unlock(&tasklist_lock);
 
-        if (flag) {
-                if (options & WNOHANG)
-                        goto end;
+        if (!retval && !(options & WNOHANG)) {
                 retval = -ERESTARTSYS;
-                if (signal_pending(current))
-                        goto end;
-                schedule();
-                goto repeat;
+                if (!signal_pending(current)) {
+                        schedule();
+                        goto repeat;
+                }
         }
-        retval = -ECHILD;
+
 end:
         current->state = TASK_RUNNING;
         remove_wait_queue(&current->signal->wait_chldexit,&wait);
diff --git a/kernel/fork.c b/kernel/fork.c
index 4bd2f516401f..adefc1131f27 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1125,8 +1125,8 @@ static struct task_struct *copy_process(unsigned long clone_flags,
          */
         p->group_leader = p;
         INIT_LIST_HEAD(&p->thread_group);
-        INIT_LIST_HEAD(&p->ptrace_children);
-        INIT_LIST_HEAD(&p->ptrace_list);
+        INIT_LIST_HEAD(&p->ptrace_entry);
+        INIT_LIST_HEAD(&p->ptraced);
 
         /* Now that the task is set up, run cgroup callbacks if
          * necessary. We need to run them before the task is visible
@@ -1198,7 +1198,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
         }
 
         if (likely(p->pid)) {
-                add_parent(p);
+                list_add_tail(&p->sibling, &p->real_parent->children);
                 if (unlikely(p->ptrace & PT_PTRACED))
                         __ptrace_link(p, current->parent);
 
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index e337390fce01..8392a9da6450 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -33,13 +33,9 @@
  */
 void __ptrace_link(struct task_struct *child, struct task_struct *new_parent)
 {
-        BUG_ON(!list_empty(&child->ptrace_list));
-        if (child->parent == new_parent)
-                return;
-        list_add(&child->ptrace_list, &child->parent->ptrace_children);
-        remove_parent(child);
+        BUG_ON(!list_empty(&child->ptrace_entry));
+        list_add(&child->ptrace_entry, &new_parent->ptraced);
         child->parent = new_parent;
-        add_parent(child);
 }
  
 /*
@@ -73,12 +69,8 @@ void __ptrace_unlink(struct task_struct *child)
         BUG_ON(!child->ptrace);
 
         child->ptrace = 0;
-        if (ptrace_reparented(child)) {
-                list_del_init(&child->ptrace_list);
-                remove_parent(child);
-                child->parent = child->real_parent;
-                add_parent(child);
-        }
+        child->parent = child->real_parent;
+        list_del_init(&child->ptrace_entry);
 
         if (task_is_traced(child))
                 ptrace_untrace(child);
@@ -492,15 +484,34 @@ int ptrace_traceme(void)
         /*
          * Are we already being traced?
          */
+repeat:
         task_lock(current);
         if (!(current->ptrace & PT_PTRACED)) {
+                /*
+                 * See ptrace_attach() comments about the locking here.
+                 */
+                unsigned long flags;
+                if (!write_trylock_irqsave(&tasklist_lock, flags)) {
+                        task_unlock(current);
+                        do {
+                                cpu_relax();
+                        } while (!write_can_lock(&tasklist_lock));
+                        goto repeat;
+                }
+
                 ret = security_ptrace(current->parent, current,
                                       PTRACE_MODE_ATTACH);
+
                 /*
                  * Set the ptrace bit in the process ptrace flags.
+                 * Then link us on our parent's ptraced list.
                  */
-                if (!ret)
+                if (!ret) {
                         current->ptrace |= PT_PTRACED;
+                        __ptrace_link(current, current->real_parent);
+                }
+
+                write_unlock_irqrestore(&tasklist_lock, flags);
         }
         task_unlock(current);
         return ret;