Re: [PATCH] tracehook: fix exit_signal=0 case

[Serge E. Hallyn]

Quoting Roland McGrath (roland@xxxxxxxxxx):
> My commit 2b2a1ff64afbadac842bbc58c5166962cf4f7664 introduced a regression
> (sorry about that) for the odd case of exit_signal=0 (e.g. clone_flags=0).
> This is not a normal use, but it's used by a case in the glibc test suite.
> 
> Dying with exit_signal=0 sends no signal, but it's supposed to wake up a
> parent's blocked wait*() calls (unlike the delayed_group_leader case).
> This fixes tracehook_notify_death() and its caller to distinguish a
> "signal 0" wakeup from the delayed_group_leader case (with no wakeup).
> 
> Signed-off-by: Roland McGrath <roland@xxxxxxxxxx>

Tested-by: Serge Hallyn <serue@xxxxxxxxxx>

thanks,
-serge

> ---
>  include/linux/tracehook.h |   21 +++++++++++++--------
>  kernel/exit.c             |    6 +++---
>  2 files changed, 16 insertions(+), 11 deletions(-)
> 
> diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
> index b187558..1253283 100644
> --- a/include/linux/tracehook.h
> +++ b/include/linux/tracehook.h
> @@ -493,16 +493,21 @@ static inline int tracehook_notify_jctl(int notify, int why)
>   * @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.
> + * A return value >= 0 means call do_notify_parent() with that signal
> + * number.  Negative return value can be %DEATH_REAP to self-reap right
> + * now, or %DEATH_DELAYED_GROUP_LEADER to a zombie without notifying our
> + * parent.  Note that a return value of 0 means a do_notify_parent() call
> + * that sends no signal, but still wakes up a parent blocked in wait*().
>   *
>   * Called with write_lock_irq(&tasklist_lock) held.
>   */
> +#define DEATH_REAP			-1
> +#define DEATH_DELAYED_GROUP_LEADER	-2
>  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;
> +		return task->ptrace ? SIGCHLD : DEATH_REAP;
>  
>  	/*
>  	 * If something other than our normal parent is ptracing us, then
> @@ -512,21 +517,21 @@ static inline int tracehook_notify_death(struct task_struct *task,
>  	if (thread_group_empty(task) && !ptrace_reparented(task))
>  		return task->exit_signal;
>  
> -	return task->ptrace ? SIGCHLD : 0;
> +	return task->ptrace ? SIGCHLD : DEATH_DELAYED_GROUP_LEADER;
>  }
>  
>  /**
>   * 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
> + * @signal:		return value from tracheook_notify_death()
>   * @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 @signal is %DEATH_REAP, this thread will self-reap.  If @signal is
> + * %DEATH_DELAYED_GROUP_LEADER, 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.
> diff --git a/kernel/exit.c b/kernel/exit.c
> index eb4d647..38ec406 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -911,10 +911,10 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
>  		tsk->exit_signal = SIGCHLD;
>  
>  	signal = tracehook_notify_death(tsk, &cookie, group_dead);
> -	if (signal > 0)
> +	if (signal >= 0)
>  		signal = do_notify_parent(tsk, signal);
>  
> -	tsk->exit_state = signal < 0 ? EXIT_DEAD : EXIT_ZOMBIE;
> +	tsk->exit_state = signal == DEATH_REAP ? EXIT_DEAD : EXIT_ZOMBIE;
>  
>  	/* mt-exec, de_thread() is waiting for us */
>  	if (thread_group_leader(tsk) &&
> @@ -927,7 +927,7 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
>  	tracehook_report_death(tsk, signal, cookie, group_dead);
>  
>  	/* If the process is dead, release it - nobody will wait for it */
> -	if (signal < 0)
> +	if (signal == DEATH_REAP)
>  		release_task(tsk);
>  }
>  
> --
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