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>

1 files changed, 12 insertions, 14 deletions

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) \