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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: Tejun Heo <tj@kernel.org> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
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3759a0d94c
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@ -1772,7 +1772,7 @@ static int zap_process(struct task_struct *start, int exit_code)
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t = start;
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do {
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task_clear_jobctl_pending(t, JOBCTL_STOP_PENDING);
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task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
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if (t != current && t->mm) {
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sigaddset(&t->pending.signal, SIGKILL);
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signal_wake_up(t, 1);
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@ -253,6 +253,9 @@ static void task_clear_jobctl_trapping(struct task_struct *task)
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* %JOBCTL_PENDING_MASK. If %JOBCTL_STOP_PENDING is being cleared, other
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* STOP bits are cleared together.
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*
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* If clearing of @mask leaves no stop or trap pending, this function calls
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* task_clear_jobctl_trapping().
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*
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* CONTEXT:
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* Must be called with @task->sighand->siglock held.
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*/
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@ -264,6 +267,9 @@ void task_clear_jobctl_pending(struct task_struct *task, unsigned int mask)
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mask |= JOBCTL_STOP_CONSUME | JOBCTL_STOP_DEQUEUED;
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task->jobctl &= ~mask;
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if (!(task->jobctl & JOBCTL_PENDING_MASK))
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task_clear_jobctl_trapping(task);
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}
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/**
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@ -933,7 +939,7 @@ static void complete_signal(int sig, struct task_struct *p, int group)
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signal->group_stop_count = 0;
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t = p;
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do {
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task_clear_jobctl_pending(t, JOBCTL_STOP_PENDING);
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task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
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sigaddset(&t->pending.signal, SIGKILL);
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signal_wake_up(t, 1);
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} while_each_thread(p, t);
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@ -1168,7 +1174,7 @@ int zap_other_threads(struct task_struct *p)
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p->signal->group_stop_count = 0;
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while_each_thread(p, t) {
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task_clear_jobctl_pending(t, JOBCTL_STOP_PENDING);
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task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
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count++;
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/* Don't bother with already dead threads */
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@ -1964,9 +1970,6 @@ retry:
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goto retry;
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}
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/* PTRACE_ATTACH might have raced with task killing, clear trapping */
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task_clear_jobctl_trapping(current);
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spin_unlock_irq(¤t->sighand->siglock);
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tracehook_finish_jctl();
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