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Subject[PATCH 1/3] signals: tracehook_notify_jctl change
Date
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.

Signed-off-by: Roland McGrath <roland@redhat.com>
---
include/linux/tracehook.h | 25 ++++++++++------
kernel/signal.c | 69 +++++++++++++++++++++++----------------------
2 files changed, 51 insertions(+), 43 deletions(-)

diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
index 6186a78..b622498 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
@@ -469,22 +469,29 @@ static inline int tracehook_get_signal(s

/**
* 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;
}

#define DEATH_REAP -1
diff --git a/kernel/signal.c b/kernel/signal.c
index 2a74fe8..9a0d98f 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -691,7 +691,7 @@ static int prepare_signal(int sig, struc

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().
*/
@@ -1629,29 +1629,6 @@ void ptrace_notify(int exit_code)
spin_unlock_irq(&current->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.
@@ -1662,6 +1639,7 @@ static int do_signal_stop(int signr)
{
struct signal_struct *sig = current->signal;
int stop_count;
+ int notify;

if (sig->group_stop_count > 0) {
/*
@@ -1701,8 +1679,30 @@ static int do_signal_stop(int signr)
current->exit_code = sig->group_exit_code;
__set_current_state(TASK_STOPPED);

+ /*
+ * 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 = tracehook_notify_jctl(stop_count == 0 ? CLD_STOPPED : 0,
+ CLD_STOPPED);
+
spin_unlock_irq(&current->sighand->siglock);
- finish_stop(stop_count);
+
+ if (notify) {
+ read_lock(&tasklist_lock);
+ do_notify_parent_cldstop(current, notify);
+ read_unlock(&tasklist_lock);
+ }
+
+ do {
+ schedule();
+ } while (try_to_freeze());
+ /*
+ * Now we don't run again until continued.
+ */
+ current->exit_code = 0;
+
return 1;
}

@@ -1771,14 +1771,15 @@ relock:
int why = (signal->flags & SIGNAL_STOP_CONTINUED)
? CLD_CONTINUED : CLD_STOPPED;
signal->flags &= ~SIGNAL_CLD_MASK;
- spin_unlock_irq(&sighand->siglock);

- if (unlikely(!tracehook_notify_jctl(1, why)))
- goto relock;
+ why = tracehook_notify_jctl(why, CLD_CONTINUED);
+ spin_unlock_irq(&sighand->siglock);

- 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;
}

@@ -1936,14 +1937,14 @@ void exit_signals(struct task_struct *ts
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);
}
}

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