tracehook: death

This moves the ptrace logic in task death (exit_notify) into tracehook.h
inlines.  Some code is rearranged slightly to make things nicer.  There is
no change, only cleanup.

There is one hook called with the tasklist_lock write-locked, as ptrace
needs.  There is also a new hook called after exit_state changes and
without locks.  This is a better place for tracing work to be in the
future, since it doesn't delay the whole system with locking.

Signed-off-by: Roland McGrath <roland@redhat.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Reviewed-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 69 insertions, 21 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index adb8077dc463..a95d84d0da95 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1796,7 +1796,7 @@ extern int kill_pid_info_as_uid(int, struct siginfo *, struct pid *, uid_t, uid_
 extern int kill_pgrp(struct pid *pid, int sig, int priv);
 extern int kill_pid(struct pid *pid, int sig, int priv);
 extern int kill_proc_info(int, struct siginfo *, pid_t);
-extern void do_notify_parent(struct task_struct *, int);
+extern int do_notify_parent(struct task_struct *, int);
 extern void force_sig(int, struct task_struct *);
 extern void force_sig_specific(int, struct task_struct *);
 extern int send_sig(int, struct task_struct *, int);
diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
index 6dc428dd2f38..4c50e1b57349 100644
--- a/include/linux/tracehook.h
+++ b/include/linux/tracehook.h
@@ -471,4 +471,56 @@ static inline int tracehook_notify_jctl(int notify, int why)
         return notify || (current->ptrace & PT_PTRACED);
 }
 
+/**
+ * tracehook_notify_death - task is dead, ready to notify parent
+ * @task:               @current task now exiting
+ * @death_cookie:       value to pass to tracehook_report_death()
+ * @group_dead:         nonzero if this was the last thread in the group to die
+ *
+ * Return the signal number to send our parent with do_notify_parent(), or
+ * zero to send no signal and leave a zombie, or -1 to self-reap right now.
+ *
+ * Called with write_lock_irq(&tasklist_lock) held.
+ */
+static inline int tracehook_notify_death(struct task_struct *task,
+                                         void **death_cookie, int group_dead)
+{
+        if (task->exit_signal == -1)
+                return task->ptrace ? SIGCHLD : -1;
+
+        /*
+         * If something other than our normal parent is ptracing us, then
+         * send it a SIGCHLD instead of honoring exit_signal.  exit_signal
+         * only has special meaning to our real parent.
+         */
+        if (thread_group_empty(task) && !ptrace_reparented(task))
+                return task->exit_signal;
+
+        return task->ptrace ? SIGCHLD : 0;
+}
+
+/**
+ * tracehook_report_death - task is dead and ready to be reaped
+ * @task:               @current task now exiting
+ * @signal:             signal number sent to parent, or 0 or -1
+ * @death_cookie:       value passed back from tracehook_notify_death()
+ * @group_dead:         nonzero if this was the last thread in the group to die
+ *
+ * Thread has just become a zombie or is about to self-reap.  If positive,
+ * @signal is the signal number just sent to the parent (usually %SIGCHLD).
+ * If @signal is -1, this thread will self-reap.  If @signal is 0, this is
+ * a delayed_group_leader() zombie.  The @death_cookie was passed back by
+ * tracehook_notify_death().
+ *
+ * If normal reaping is not inhibited, @task->exit_state might be changing
+ * in parallel.
+ *
+ * Called without locks.
+ */
+static inline void tracehook_report_death(struct task_struct *task,
+                                          int signal, void *death_cookie,
+                                          int group_dead)
+{
+}
+
 #endif  /* <linux/tracehook.h> */
diff --git a/kernel/exit.c b/kernel/exit.c
index da28745f7c38..6cdf60712bd2 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -885,7 +885,8 @@ static void forget_original_parent(struct task_struct *father)
  */
 static void exit_notify(struct task_struct *tsk, int group_dead)
 {
-        int state;
+        int signal;
+        void *cookie;
 
         /*
          * This does two things:
@@ -922,22 +923,11 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
             !capable(CAP_KILL))
                 tsk->exit_signal = SIGCHLD;
 
-        /* If something other than our normal parent is ptracing us, then
-         * send it a SIGCHLD instead of honoring exit_signal.  exit_signal
-         * only has special meaning to our real parent.
-         */
-        if (!task_detached(tsk) && thread_group_empty(tsk)) {
-                int signal = ptrace_reparented(tsk) ?
-                                SIGCHLD : tsk->exit_signal;
-                do_notify_parent(tsk, signal);
-        } else if (tsk->ptrace) {
-                do_notify_parent(tsk, SIGCHLD);
-        }
+        signal = tracehook_notify_death(tsk, &cookie, group_dead);
+        if (signal > 0)
+                signal = do_notify_parent(tsk, signal);
 
-        state = EXIT_ZOMBIE;
-        if (task_detached(tsk) && likely(!tsk->ptrace))
-                state = EXIT_DEAD;
-        tsk->exit_state = state;
+        tsk->exit_state = signal < 0 ? EXIT_DEAD : EXIT_ZOMBIE;
 
         /* mt-exec, de_thread() is waiting for us */
         if (thread_group_leader(tsk) &&
@@ -947,8 +937,10 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
 
         write_unlock_irq(&tasklist_lock);
 
+        tracehook_report_death(tsk, signal, cookie, group_dead);
+
         /* If the process is dead, release it - nobody will wait for it */
-        if (state == EXIT_DEAD)
+        if (signal < 0)
                 release_task(tsk);
 }
 
diff --git a/kernel/signal.c b/kernel/signal.c
index e9e699f4b1bd..0e862d3130ff 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1326,9 +1326,11 @@ static inline void __wake_up_parent(struct task_struct *p,
 /*
  * Let a parent know about the death of a child.
  * For a stopped/continued status change, use do_notify_parent_cldstop instead.
+ *
+ * Returns -1 if our parent ignored us and so we've switched to
+ * self-reaping, or else @sig.
  */
-
-void do_notify_parent(struct task_struct *tsk, int sig)
+int do_notify_parent(struct task_struct *tsk, int sig)
 {
         struct siginfo info;
         unsigned long flags;
@@ -1399,12 +1401,14 @@ void do_notify_parent(struct task_struct *tsk, int sig)
                  */
                 tsk->exit_signal = -1;
                 if (psig->action[SIGCHLD-1].sa.sa_handler == SIG_IGN)
-                        sig = 0;
+                        sig = -1;
         }
         if (valid_signal(sig) && sig > 0)
                 __group_send_sig_info(sig, &info, tsk->parent);
         __wake_up_parent(tsk, tsk->parent);
         spin_unlock_irqrestore(&psig->siglock, flags);
+
+        return sig;
 }
 
 static void do_notify_parent_cldstop(struct task_struct *tsk, int why)