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job control: make task_clear_jobctl_pending() clear TRAPPING automatically

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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>
This commit is contained in:
Tejun Heo 2011-06-02 11:14:00 +02:00 committed by Oleg Nesterov
parent 3759a0d94c
commit 6dfca32984
2 changed files with 9 additions and 6 deletions
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2
fs/exec.c
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@ -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);

13
kernel/signal.c
View file

@ -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 @@ static int do_signal_stop(int signr)
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();