signals: tracehook_notify_jctl change
This changes tracehook_notify_jctl() so it's called with the siglock held,
and changes its argument and return value definition. These clean-ups
make it a better fit for what new tracing hooks need to check.
Tracing needs the siglock here, held from the time TASK_STOPPED was set,
to avoid potential SIGCONT races if it wants to allow any blocking in its
tracing hooks.
This also folds the finish_stop() function into its caller
do_signal_stop(). The function is short, called only once and only
unconditionally. It aids readability to fold it in.
[oleg@redhat.com: do not call tracehook_notify_jctl() in TASK_STOPPED state]
[oleg@redhat.com: introduce tracehook_finish_jctl() helper]
Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
index 17ba82ef..1eb44a9 100644
--- a/include/linux/tracehook.h
+++ b/include/linux/tracehook.h
@@ -1,7 +1,7 @@
/*
* Tracing hooks
*
- * Copyright (C) 2008 Red Hat, Inc. All rights reserved.
+ * Copyright (C) 2008-2009 Red Hat, Inc. All rights reserved.
*
* This copyrighted material is made available to anyone wishing to use,
* modify, copy, or redistribute it subject to the terms and conditions
@@ -463,22 +463,38 @@
/**
* tracehook_notify_jctl - report about job control stop/continue
- * @notify: nonzero if this is the last thread in the group to stop
+ * @notify: zero, %CLD_STOPPED or %CLD_CONTINUED
* @why: %CLD_STOPPED or %CLD_CONTINUED
*
* This is called when we might call do_notify_parent_cldstop().
- * It's called when about to stop for job control; we are already in
- * %TASK_STOPPED state, about to call schedule(). It's also called when
- * a delayed %CLD_STOPPED or %CLD_CONTINUED report is ready to be made.
*
- * Return nonzero to generate a %SIGCHLD with @why, which is
- * normal if @notify is nonzero.
+ * @notify is zero if we would not ordinarily send a %SIGCHLD,
+ * or is the %CLD_STOPPED or %CLD_CONTINUED .si_code for %SIGCHLD.
*
- * Called with no locks held.
+ * @why is %CLD_STOPPED when about to stop for job control;
+ * we are already in %TASK_STOPPED state, about to call schedule().
+ * It might also be that we have just exited (check %PF_EXITING),
+ * but need to report that a group-wide stop is complete.
+ *
+ * @why is %CLD_CONTINUED when waking up after job control stop and
+ * ready to make a delayed @notify report.
+ *
+ * Return the %CLD_* value for %SIGCHLD, or zero to generate no signal.
+ *
+ * Called with the siglock held.
*/
static inline int tracehook_notify_jctl(int notify, int why)
{
- return notify || (current->ptrace & PT_PTRACED);
+ return notify ?: (current->ptrace & PT_PTRACED) ? why : 0;
+}
+
+/**
+ * tracehook_finish_jctl - report about return from job control stop
+ *
+ * This is called by do_signal_stop() after wakeup.
+ */
+static inline void tracehook_finish_jctl(void)
+{
}
#define DEATH_REAP -1
diff --git a/kernel/signal.c b/kernel/signal.c
index 534ea81..5d3b3f8 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -705,7 +705,7 @@
if (why) {
/*
- * The first thread which returns from finish_stop()
+ * The first thread which returns from do_signal_stop()
* will take ->siglock, notice SIGNAL_CLD_MASK, and
* notify its parent. See get_signal_to_deliver().
*/
@@ -1664,29 +1664,6 @@
spin_unlock_irq(¤t->sighand->siglock);
}
-static void
-finish_stop(int stop_count)
-{
- /*
- * If there are no other threads in the group, or if there is
- * a group stop in progress and we are the last to stop,
- * report to the parent. When ptraced, every thread reports itself.
- */
- if (tracehook_notify_jctl(stop_count == 0, CLD_STOPPED)) {
- read_lock(&tasklist_lock);
- do_notify_parent_cldstop(current, CLD_STOPPED);
- read_unlock(&tasklist_lock);
- }
-
- do {
- schedule();
- } while (try_to_freeze());
- /*
- * Now we don't run again until continued.
- */
- current->exit_code = 0;
-}
-
/*
* This performs the stopping for SIGSTOP and other stop signals.
* We have to stop all threads in the thread group.
@@ -1696,15 +1673,9 @@
static int do_signal_stop(int signr)
{
struct signal_struct *sig = current->signal;
- int stop_count;
+ int notify;
- if (sig->group_stop_count > 0) {
- /*
- * There is a group stop in progress. We don't need to
- * start another one.
- */
- stop_count = --sig->group_stop_count;
- } else {
+ if (!sig->group_stop_count) {
struct task_struct *t;
if (!likely(sig->flags & SIGNAL_STOP_DEQUEUED) ||
@@ -1716,7 +1687,7 @@
*/
sig->group_exit_code = signr;
- stop_count = 0;
+ sig->group_stop_count = 1;
for (t = next_thread(current); t != current; t = next_thread(t))
/*
* Setting state to TASK_STOPPED for a group
@@ -1725,19 +1696,44 @@
*/
if (!(t->flags & PF_EXITING) &&
!task_is_stopped_or_traced(t)) {
- stop_count++;
+ sig->group_stop_count++;
signal_wake_up(t, 0);
}
- sig->group_stop_count = stop_count;
+ }
+ /*
+ * If there are no other threads in the group, or if there is
+ * a group stop in progress and we are the last to stop, report
+ * to the parent. When ptraced, every thread reports itself.
+ */
+ notify = sig->group_stop_count == 1 ? CLD_STOPPED : 0;
+ notify = tracehook_notify_jctl(notify, CLD_STOPPED);
+ /*
+ * tracehook_notify_jctl() can drop and reacquire siglock, so
+ * we keep ->group_stop_count != 0 before the call. If SIGCONT
+ * or SIGKILL comes in between ->group_stop_count == 0.
+ */
+ if (sig->group_stop_count) {
+ if (!--sig->group_stop_count)
+ sig->flags = SIGNAL_STOP_STOPPED;
+ current->exit_code = sig->group_exit_code;
+ __set_current_state(TASK_STOPPED);
+ }
+ spin_unlock_irq(¤t->sighand->siglock);
+
+ if (notify) {
+ read_lock(&tasklist_lock);
+ do_notify_parent_cldstop(current, notify);
+ read_unlock(&tasklist_lock);
}
- if (stop_count == 0)
- sig->flags = SIGNAL_STOP_STOPPED;
- current->exit_code = sig->group_exit_code;
- __set_current_state(TASK_STOPPED);
+ /* Now we don't run again until woken by SIGCONT or SIGKILL */
+ do {
+ schedule();
+ } while (try_to_freeze());
- spin_unlock_irq(¤t->sighand->siglock);
- finish_stop(stop_count);
+ tracehook_finish_jctl();
+ current->exit_code = 0;
+
return 1;
}
@@ -1806,14 +1802,15 @@
int why = (signal->flags & SIGNAL_STOP_CONTINUED)
? CLD_CONTINUED : CLD_STOPPED;
signal->flags &= ~SIGNAL_CLD_MASK;
+
+ why = tracehook_notify_jctl(why, CLD_CONTINUED);
spin_unlock_irq(&sighand->siglock);
- if (unlikely(!tracehook_notify_jctl(1, why)))
- goto relock;
-
- read_lock(&tasklist_lock);
- do_notify_parent_cldstop(current->group_leader, why);
- read_unlock(&tasklist_lock);
+ if (why) {
+ read_lock(&tasklist_lock);
+ do_notify_parent_cldstop(current->group_leader, why);
+ read_unlock(&tasklist_lock);
+ }
goto relock;
}
@@ -1978,14 +1975,14 @@
if (unlikely(tsk->signal->group_stop_count) &&
!--tsk->signal->group_stop_count) {
tsk->signal->flags = SIGNAL_STOP_STOPPED;
- group_stop = 1;
+ group_stop = tracehook_notify_jctl(CLD_STOPPED, CLD_STOPPED);
}
out:
spin_unlock_irq(&tsk->sighand->siglock);
- if (unlikely(group_stop) && tracehook_notify_jctl(1, CLD_STOPPED)) {
+ if (unlikely(group_stop)) {
read_lock(&tasklist_lock);
- do_notify_parent_cldstop(tsk, CLD_STOPPED);
+ do_notify_parent_cldstop(tsk, group_stop);
read_unlock(&tasklist_lock);
}
}
