ptrace children revamp
ptrace no longer fiddles with the children/sibling links, and the
old ptrace_children list is gone. Now ptrace, whether of one's own
children or another's via PTRACE_ATTACH, just uses the new ptraced
list instead.
There should be no user-visible difference that matters. The only
change is the order in which do_wait() sees multiple stopped
children and stopped ptrace attachees. Since wait_task_stopped()
was changed earlier so it no longer reorders the children list, we
already know this won't cause any new problems.
Signed-off-by: Roland McGrath <roland@redhat.com>
diff --git a/kernel/exit.c b/kernel/exit.c
index 7453356..1e90982 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -71,7 +71,7 @@
__get_cpu_var(process_counts)--;
}
list_del_rcu(&p->thread_group);
- remove_parent(p);
+ list_del_init(&p->sibling);
}
/*
@@ -152,6 +152,18 @@
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 @@
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 @@
ptrace_unlink(current);
/* Reparent to init */
- remove_parent(current);
current->real_parent = current->parent = kthreadd_task;
- add_parent(current);
+ list_move_tail(¤t->sibling, ¤t->real_parent->children);
/* Set the exit signal to SIGCHLD so we signal init on exit */
current->exit_signal = SIGCHLD;
@@ -692,37 +702,71 @@
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)
+{
+ struct task_struct *p, *n;
+
+ 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.
+ */
+ 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_detached(p)) {
+ /*
+ * Mark it as in the process of being reaped.
+ */
+ 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);
- /* 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.
- */
- p->ptrace = 0;
- remove_parent(p);
- p->parent = p->real_parent;
- add_parent(p);
-
- if (task_is_traced(p)) {
- /*
- * If it was at a trace stop, turn it into
- * a normal stop since it's no longer being
- * traced.
- */
- ptrace_untrace(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 @@
/* 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 @@
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 @@
}
} 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 @@
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 @@
* 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 @@
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 @@
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 @@
*/
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 @@
* 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 @@
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 @@
*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 @@
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 @@
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;