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Commit 7dd3db54 authored by Tejun Heo's avatar Tejun Heo Committed by Oleg Nesterov
Browse files

job control: introduce task_set_jobctl_pending() 



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: default avatarTejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
parent 6dfca329

include/linux/sched.h

+2 −0
Original line number Diff line number Diff line
@@ -1819,6 +1819,8 @@ extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t * 


#define JOBCTL_PENDING_MASK	JOBCTL_STOP_PENDING



extern bool task_set_jobctl_pending(struct task_struct *task,

				    unsigned int mask);

extern void task_clear_jobctl_pending(struct task_struct *task,

				      unsigned int mask);

kernel/ptrace.c

+3 −3
Original line number Diff line number Diff line
@@ -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);

kernel/signal.c

+40 −6
Original line number Diff line number Diff line
@@ -223,6 +223,39 @@ static inline void print_dropped_signal(int sig) 
				current->comm, current->pid, sig);

}



/**

 * task_set_jobctl_pending - set jobctl pending bits

 * @task: target task

 * @mask: pending bits to set

 *

 * Clear @mask from @task->jobctl.  @mask must be subset of

 * %JOBCTL_PENDING_MASK | %JOBCTL_STOP_CONSUME | %JOBCTL_STOP_SIGMASK |

 * %JOBCTL_TRAPPING.  If stop signo is being set, the existing signo is

 * cleared.  If @task is already being killed or exiting, this function

 * becomes noop.

 *

 * CONTEXT:

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

 *

 * RETURNS:

 * %true if @mask is set, %false if made noop because @task was dying.

 */

bool task_set_jobctl_pending(struct task_struct *task, unsigned int mask)

{

	BUG_ON(mask & ~(JOBCTL_PENDING_MASK | JOBCTL_STOP_CONSUME |

			JOBCTL_STOP_SIGMASK | JOBCTL_TRAPPING));

	BUG_ON((mask & JOBCTL_TRAPPING) && !(mask & JOBCTL_PENDING_MASK));



	if (unlikely(fatal_signal_pending(task) || (task->flags & PF_EXITING)))

		return false;



	if (mask & JOBCTL_STOP_SIGMASK)

		task->jobctl &= ~JOBCTL_STOP_SIGMASK;



	task->jobctl |= mask;

	return true;

}



/**

 * task_clear_jobctl_trapping - clear jobctl trapping bit

 * @task: target task
@@ -1902,19 +1935,20 @@ static int do_signal_stop(int signr) 
		else

			WARN_ON_ONCE(!task_ptrace(current));



		current->jobctl &= ~JOBCTL_STOP_SIGMASK;

		current->jobctl |= signr | gstop;

		sig->group_stop_count = 1;

		sig->group_stop_count = 0;



		if (task_set_jobctl_pending(current, signr | gstop))

			sig->group_stop_count++;



		for (t = next_thread(current); t != current;

		     t = next_thread(t)) {

			t->jobctl &= ~JOBCTL_STOP_SIGMASK;

			/*

			 * Setting state to TASK_STOPPED for a group

			 * stop is always done with the siglock held,

			 * so this check has no races.

			 */

			if (!(t->flags & PF_EXITING) && !task_is_stopped(t)) {

				t->jobctl |= signr | gstop;

			if (!task_is_stopped(t) &&

			    task_set_jobctl_pending(t, signr | gstop)) {

				sig->group_stop_count++;

				signal_wake_up(t, 0);

			}