forget_original_parent: split out the un-ptrace part

By discussion with Roland.

- Rename ptrace_exit() to exit_ptrace(), and change it to do all the
  necessary work with ->ptraced list by its own.

- Move this code from exit.c to ptrace.c

- Update the comment in ptrace_detach() to explain the rechecking of
  the child->ptrace.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "Metzger, Markus T" <markus.t.metzger@intel.com>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 88 insertions, 92 deletions

diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index 1a2b0cb55535..67c15653fc23 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -94,7 +94,7 @@ extern void ptrace_notify(int exit_code);
 extern void __ptrace_link(struct task_struct *child,
                           struct task_struct *new_parent);
 extern void __ptrace_unlink(struct task_struct *child);
-extern int __ptrace_detach(struct task_struct *tracer, struct task_struct *p);
+extern void exit_ptrace(struct task_struct *tracer);
 extern void ptrace_fork(struct task_struct *task, unsigned long clone_flags);
 #define PTRACE_MODE_READ   1
 #define PTRACE_MODE_ATTACH 2
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 9186f8c5d5f2..b47c94e7560b 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2061,6 +2061,11 @@ static inline int thread_group_empty(struct task_struct *p)
 #define delay_group_leader(p) \
                 (thread_group_leader(p) && !thread_group_empty(p))
 
+static inline int task_detached(struct task_struct *p)
+{
+        return p->exit_signal == -1;
+}
+
 /*
  * Protects ->fs, ->files, ->mm, ->group_info, ->comm, keyring
  * subscriptions and synchronises with wait4().  Also used in procfs.  Also
diff --git a/kernel/exit.c b/kernel/exit.c
index 3e09b7cb3b20..506693dfdd4e 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -61,11 +61,6 @@ DEFINE_TRACE(sched_process_wait);
 
 static void exit_mm(struct task_struct * tsk);
 
-static inline int task_detached(struct task_struct *p)
-{
-        return p->exit_signal == -1;
-}
-
 static void __unhash_process(struct task_struct *p)
 {
         nr_threads--;
@@ -731,85 +726,6 @@ static void exit_mm(struct task_struct * tsk)
         mmput(mm);
 }
 
-/*
- * Called with irqs disabled, returns true if childs should reap themselves.
- */
-static int ignoring_children(struct sighand_struct *sigh)
-{
-        int ret;
-        spin_lock(&sigh->siglock);
-        ret = (sigh->action[SIGCHLD-1].sa.sa_handler == SIG_IGN) ||
-              (sigh->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDWAIT);
-        spin_unlock(&sigh->siglock);
-        return ret;
-}
-
-/* Returns nonzero if the tracee should be released. */
-int __ptrace_detach(struct task_struct *tracer, struct task_struct *p)
-{
-        __ptrace_unlink(p);
-
-        if (p->exit_state != EXIT_ZOMBIE)
-                return 0;
-        /*
-         * 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 we return true.
-         *
-         * 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.
-         */
-        if (!task_detached(p) && thread_group_empty(p)) {
-                if (!same_thread_group(p->real_parent, tracer))
-                        do_notify_parent(p, p->exit_signal);
-                else if (ignoring_children(tracer->sighand))
-                        p->exit_signal = -1;
-        }
-
-        if (!task_detached(p))
-                return 0;
-
-        /* Mark it as in the process of being reaped. */
-        p->exit_state = EXIT_DEAD;
-        return 1;
-}
-
-/*
- * 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) {
-                if (__ptrace_detach(parent, p))
-                        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);
-        }
-}
-
 /* Returns nonzero if the child should be released. */
 static int reparent_thread(struct task_struct *p, struct task_struct *father)
 {
@@ -894,12 +810,10 @@ static void forget_original_parent(struct task_struct *father)
         struct task_struct *p, *n, *reaper;
         LIST_HEAD(ptrace_dead);
 
+        exit_ptrace(father);
+
         write_lock_irq(&tasklist_lock);
         reaper = find_new_reaper(father);
-        /*
-         * First clean up ptrace if we were using it.
-         */
-        ptrace_exit(father, &ptrace_dead);
 
         list_for_each_entry_safe(p, n, &father->children, sibling) {
                 p->real_parent = reaper;
@@ -914,7 +828,10 @@ static void forget_original_parent(struct task_struct *father)
         write_unlock_irq(&tasklist_lock);
         BUG_ON(!list_empty(&father->children));
 
-        ptrace_exit_finish(father, &ptrace_dead);
+        list_for_each_entry_safe(p, n, &ptrace_dead, ptrace_entry) {
+                list_del_init(&p->ptrace_entry);
+                release_task(p);
+        }
 }
 
 /*
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index ee553b6ad125..f5a9fa5aafa1 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -235,9 +235,57 @@ out:
         return retval;
 }
 
+/*
+ * Called with irqs disabled, returns true if childs should reap themselves.
+ */
+static int ignoring_children(struct sighand_struct *sigh)
+{
+        int ret;
+        spin_lock(&sigh->siglock);
+        ret = (sigh->action[SIGCHLD-1].sa.sa_handler == SIG_IGN) ||
+              (sigh->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDWAIT);
+        spin_unlock(&sigh->siglock);
+        return ret;
+}
+
+/*
+ * Called with tasklist_lock held for writing.
+ * Unlink a traced task, and clean it up if it was a traced zombie.
+ * Return true if it needs to be reaped with release_task().
+ * (We can't call release_task() here because we already hold tasklist_lock.)
+ *
+ * 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, return true.
+ *
+ * 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.
+ */
+static bool __ptrace_detach(struct task_struct *tracer, struct task_struct *p)
+{
+        __ptrace_unlink(p);
+
+        if (p->exit_state == EXIT_ZOMBIE) {
+                if (!task_detached(p) && thread_group_empty(p)) {
+                        if (!same_thread_group(p->real_parent, tracer))
+                                do_notify_parent(p, p->exit_signal);
+                        else if (ignoring_children(tracer->sighand))
+                                p->exit_signal = -1;
+                }
+                if (task_detached(p)) {
+                        /* Mark it as in the process of being reaped. */
+                        p->exit_state = EXIT_DEAD;
+                        return true;
+                }
+        }
+
+        return false;
+}
+
 int ptrace_detach(struct task_struct *child, unsigned int data)
 {
-        int dead = 0;
+        bool dead = false;
 
         if (!valid_signal(data))
                 return -EIO;
@@ -247,7 +295,10 @@ int ptrace_detach(struct task_struct *child, unsigned int data)
         clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 
         write_lock_irq(&tasklist_lock);
-        /* protect against de_thread()->release_task() */
+        /*
+         * This child can be already killed. Make sure de_thread() or
+         * our sub-thread doing do_wait() didn't do release_task() yet.
+         */
         if (child->ptrace) {
                 child->exit_code = data;
 
@@ -264,6 +315,29 @@ int ptrace_detach(struct task_struct *child, unsigned int data)
         return 0;
 }
 
+/*
+ * Detach all tasks we were using ptrace on.
+ */
+void exit_ptrace(struct task_struct *tracer)
+{
+        struct task_struct *p, *n;
+        LIST_HEAD(ptrace_dead);
+
+        write_lock_irq(&tasklist_lock);
+        list_for_each_entry_safe(p, n, &tracer->ptraced, ptrace_entry) {
+                if (__ptrace_detach(tracer, p))
+                        list_add(&p->ptrace_entry, &ptrace_dead);
+        }
+        write_unlock_irq(&tasklist_lock);
+
+        BUG_ON(!list_empty(&tracer->ptraced));
+
+        list_for_each_entry_safe(p, n, &ptrace_dead, ptrace_entry) {
+                list_del_init(&p->ptrace_entry);
+                release_task(p);
+        }
+}
+
 int ptrace_readdata(struct task_struct *tsk, unsigned long src, char __user *dst, int len)
 {
         int copied = 0;