Commit 6dfca329 authored by Tejun Heo's avatar Tejun Heo Committed by Oleg Nesterov
Browse files

job control: make task_clear_jobctl_pending() clear TRAPPING automatically 



JOBCTL_TRAPPING indicates that ptracer is waiting for tracee to
(re)transit into TRACED.  task_clear_jobctl_pending() must be called
when either tracee enters TRACED or the transition is cancelled for
some reason.  The former is achieved by explicitly calling
task_clear_jobctl_pending() in ptrace_stop() and the latter by calling
it at the end of do_signal_stop().

Calling task_clear_jobctl_trapping() at the end of do_signal_stop()
limits the scope TRAPPING can be used and is fragile in that seemingly
unrelated changes to tracee's control flow can lead to stuck TRAPPING.

We already have task_clear_jobctl_pending() calls on those cancelling
events to clear JOBCTL_STOP_PENDING.  Cancellations can be handled by
making those call sites use JOBCTL_PENDING_MASK instead and updating
task_clear_jobctl_pending() such that task_clear_jobctl_trapping() is
called automatically if no stop/trap is pending.

This patch makes the above changes and removes the fallback
task_clear_jobctl_trapping() call from do_signal_stop().

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
parent 3759a0d9

fs/exec.c

+1 −1
Original line number Diff line number Diff line
@@ -1772,7 +1772,7 @@ static int zap_process(struct task_struct *start, int exit_code) 


	t = start;

	do {

		task_clear_jobctl_pending(t, JOBCTL_STOP_PENDING);

		task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);

		if (t != current && t->mm) {

			sigaddset(&t->pending.signal, SIGKILL);

			signal_wake_up(t, 1);

kernel/signal.c

+8 −5
Original line number Diff line number Diff line
@@ -253,6 +253,9 @@ static void task_clear_jobctl_trapping(struct task_struct *task) 
 * %JOBCTL_PENDING_MASK.  If %JOBCTL_STOP_PENDING is being cleared, other

 * STOP bits are cleared together.

 *

 * If clearing of @mask leaves no stop or trap pending, this function calls

 * task_clear_jobctl_trapping().

 *

 * CONTEXT:

 * Must be called with @task->sighand->siglock held.

 */
@@ -264,6 +267,9 @@ void task_clear_jobctl_pending(struct task_struct *task, unsigned int mask) 
		mask |= JOBCTL_STOP_CONSUME | JOBCTL_STOP_DEQUEUED;



	task->jobctl &= ~mask;



	if (!(task->jobctl & JOBCTL_PENDING_MASK))

		task_clear_jobctl_trapping(task);

}



/**
@@ -933,7 +939,7 @@ static void complete_signal(int sig, struct task_struct *p, int group) 
			signal->group_stop_count = 0;

			t = p;

			do {

				task_clear_jobctl_pending(t, JOBCTL_STOP_PENDING);

				task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);

				sigaddset(&t->pending.signal, SIGKILL);

				signal_wake_up(t, 1);

			} while_each_thread(p, t);
@@ -1168,7 +1174,7 @@ int zap_other_threads(struct task_struct *p) 
	p->signal->group_stop_count = 0;



	while_each_thread(p, t) {

		task_clear_jobctl_pending(t, JOBCTL_STOP_PENDING);

		task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);

		count++;



		/* Don't bother with already dead threads */
@@ -1964,9 +1970,6 @@ retry: 
		goto retry;

	}



	/* PTRACE_ATTACH might have raced with task killing, clear trapping */

	task_clear_jobctl_trapping(current);



	spin_unlock_irq(&current->sighand->siglock);



	tracehook_finish_jctl();

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