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job control: introduce task_set_jobctl_pending()

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task->jobctl currently hosts JOBCTL_STOP_PENDING and will host TRAP
pending bits too.  Setting pending conditions on a dying task may make
the task unkillable.  Currently, each setting site is responsible for
checking for the condition but with to-be-added job control traps this
becomes too fragile.

This patch adds task_set_jobctl_pending() which should be used when
setting task->jobctl bits to schedule a stop or trap.  The function
performs the followings to ease setting pending bits.

* Sanity checks.

* If fatal signal is pending or PF_EXITING is set, no bit is set.

* STOP_SIGMASK is automatically cleared if new value is being set.

do_signal_stop() and ptrace_attach() are updated to use
task_set_jobctl_pending() instead of setting STOP_PENDING explicitly.
The surrounding structures around setting are changed to fit
task_set_jobctl_pending() better but there should be no userland
visible behavior difference.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
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 6dfca32984
commit 7dd3db54e7
3 changed files with 45 additions and 9 deletions
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6
kernel/ptrace.c
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@ -256,10 +256,10 @@ static int ptrace_attach(struct task_struct *task)
* The following task_is_stopped() test is safe as both transitions
* in and out of STOPPED are protected by siglock.
*/
if (task_is_stopped(task)) {
task->jobctl |= JOBCTL_STOP_PENDING | JOBCTL_TRAPPING;
if (task_is_stopped(task) &&
task_set_jobctl_pending(task,
JOBCTL_STOP_PENDING | JOBCTL_TRAPPING))
signal_wake_up(task, 1);
}
spin_unlock(&task->sighand->siglock);