ptrace: ensure JOBCTL_STOP_SIGMASK is not zero after detach

This is the temporary simple fix for 3.2, we need more changes in this area. 1. do_signal_stop() assumes that the running untraced thread in the stopped thread group is not possible. This was our goal but it is not yet achieved: a stopped-but-resumed tracee can clone the running thread which can initiate another group-stop. Remove WARN_ON_ONCE(!current->ptrace). 2. A new thread always starts with ->jobctl = 0. If it is auto-attached and this group is stopped, __ptrace_unlink() sets JOBCTL_STOP_PENDING but JOBCTL_STOP_SIGMASK part is zero, this triggers WANR_ON(!signr) in do_jobctl_trap() if another debugger attaches. Change __ptrace_unlink() to set the artificial SIGSTOP for report. Alternatively we could change ptrace_init_task() to copy signr from current, but this means we can copy it for no reason and hide the possible similar problems.

Oleg Nesterov committed 14 years ago

Commit 8a889511 parent 50b8d252 files · +12 −3Browse files

Unified · Split

2 files

kernel/ptrace.c +12 −1
kernel/signal.c +0 −2

kernel/ptrace.c+12−1

@@ -96,9 +96,20 @@ void __ptrace_unlink(struct task_struct *child) · 95 unmodified lines
96	*/	96	*/
97	if (!(child->flags & PF_EXITING) &&	97	if (!(child->flags & PF_EXITING) &&
98	(child->signal->flags & SIGNAL_STOP_STOPPED \|\|	98	(child->signal->flags & SIGNAL_STOP_STOPPED \|\|
99	child->signal->group_stop_count))	99	child->signal->group_stop_count)) {
100	child->jobctl \|= JOBCTL_STOP_PENDING;	100	child->jobctl \|= JOBCTL_STOP_PENDING;
101		101
		102	/*
		103	* This is only possible if this thread was cloned by the
		104	* traced task running in the stopped group, set the signal
		105	* for the future reports.
		106	* FIXME: we should change ptrace_init_task() to handle this
		107	* case.
		108	*/
		109	if (!(child->jobctl & JOBCTL_STOP_SIGMASK))
		110	child->jobctl \|= SIGSTOP;
		111	}
		112
102	/*	113	/*
103	* If transition to TASK_STOPPED is pending or in TASK_TRACED, kick	114	* If transition to TASK_STOPPED is pending or in TASK_TRACED, kick
104	* @child in the butt. Note that @resume should be used iff @child	115	* @child in the butt. Note that @resume should be used iff @child

kernel/signal.c+0−2

@@ -1994,8 +1994,6 @@ static bool do_signal_stop(int signr) · 1993 unmodified lines
1994	*/	1994	*/
1995	if (!(sig->flags & SIGNAL_STOP_STOPPED))	1995	if (!(sig->flags & SIGNAL_STOP_STOPPED))
1996	sig->group_exit_code = signr;	1996	sig->group_exit_code = signr;
1997	else
1998	WARN_ON_ONCE(!current->ptrace);
1999		1997
2000	sig->group_stop_count = 0;	1998	sig->group_stop_count = 0;
2001		1999