[PATCH 16/23] tracehook: death

Roland McGrath
2008-07-17T07:34:08Z

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>
---
include/linux/sched.h | 2 +-
include/linux/tracehook.h | 52 +++++++++++++++++++++++++++++++++++++++++++++
kernel/exit.c | 26 +++++++--------------
kernel/signal.c | 10 ++++++--
4 files changed, 69 insertions(+), 21 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 1941d8b..c58e8ab 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1785,7 +1785,7 @@ 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 6dc428d..4c50e1b 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 a416a84..78c6307 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -861,7 +861,8 @@ 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:
@@ -898,22 +899,11 @@ 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) &&
@@ -923,8 +913,10 @@ 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 9b8d94a..cbec18e 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1346,9 +1346,11 @@ 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;
@@ -1420,12 +1422,14 @@ 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)