Commit e91b4816 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Jens Axboe
Browse files

task_work: teach task_work_add() to do signal_wake_up() 



So that the target task will exit the wait_event_interruptible-like
loop and call task_work_run() asap.

The patch turns "bool notify" into 0,TWA_RESUME,TWA_SIGNAL enum, the
new TWA_SIGNAL flag implies signal_wake_up().  However, it needs to
avoid the race with recalc_sigpending(), so the patch also adds the
new JOBCTL_TASK_WORK bit included in JOBCTL_PENDING_MASK.

TODO: once this patch is merged we need to change all current users
of task_work_add(notify = true) to use TWA_RESUME.

Cc: stable@vger.kernel.org # v5.7
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent d60b5fbc

include/linux/sched/jobctl.h

+3 −1
Original line number Diff line number Diff line
@@ -19,6 +19,7 @@ struct task_struct; 
#define JOBCTL_TRAPPING_BIT	21	/* switching to TRACED */

#define JOBCTL_LISTENING_BIT	22	/* ptracer is listening for events */

#define JOBCTL_TRAP_FREEZE_BIT	23	/* trap for cgroup freezer */

#define JOBCTL_TASK_WORK_BIT	24	/* set by TWA_SIGNAL */



#define JOBCTL_STOP_DEQUEUED	(1UL << JOBCTL_STOP_DEQUEUED_BIT)

#define JOBCTL_STOP_PENDING	(1UL << JOBCTL_STOP_PENDING_BIT)
@@ -28,9 +29,10 @@ struct task_struct; 
#define JOBCTL_TRAPPING		(1UL << JOBCTL_TRAPPING_BIT)

#define JOBCTL_LISTENING	(1UL << JOBCTL_LISTENING_BIT)

#define JOBCTL_TRAP_FREEZE	(1UL << JOBCTL_TRAP_FREEZE_BIT)

#define JOBCTL_TASK_WORK	(1UL << JOBCTL_TASK_WORK_BIT)



#define JOBCTL_TRAP_MASK	(JOBCTL_TRAP_STOP | JOBCTL_TRAP_NOTIFY)

#define JOBCTL_PENDING_MASK	(JOBCTL_STOP_PENDING | JOBCTL_TRAP_MASK)

#define JOBCTL_PENDING_MASK	(JOBCTL_STOP_PENDING | JOBCTL_TRAP_MASK | JOBCTL_TASK_WORK)



extern bool task_set_jobctl_pending(struct task_struct *task, unsigned long mask);

extern void task_clear_jobctl_trapping(struct task_struct *task);

include/linux/task_work.h

+4 −1
Original line number Diff line number Diff line
@@ -13,7 +13,10 @@ init_task_work(struct callback_head *twork, task_work_func_t func) 
	twork->func = func;

}



int task_work_add(struct task_struct *task, struct callback_head *twork, bool);

#define TWA_RESUME	1

#define TWA_SIGNAL	2

int task_work_add(struct task_struct *task, struct callback_head *twork, int);



struct callback_head *task_work_cancel(struct task_struct *, task_work_func_t);

void task_work_run(void);

kernel/signal.c

+7 −3
Original line number Diff line number Diff line
@@ -2529,9 +2529,6 @@ bool get_signal(struct ksignal *ksig) 
	struct signal_struct *signal = current->signal;

	int signr;



	if (unlikely(current->task_works))

		task_work_run();



	if (unlikely(uprobe_deny_signal()))

		return false;
@@ -2544,6 +2541,13 @@ bool get_signal(struct ksignal *ksig) 


relock:

	spin_lock_irq(&sighand->siglock);

	current->jobctl &= ~JOBCTL_TASK_WORK;

	if (unlikely(current->task_works)) {

		spin_unlock_irq(&sighand->siglock);

		task_work_run();

		goto relock;

	}



	/*

	 * Every stopped thread goes here after wakeup. Check to see if

	 * we should notify the parent, prepare_signal(SIGCONT) encodes

kernel/task_work.c

+14 −2
Original line number Diff line number Diff line
@@ -25,9 +25,10 @@ static struct callback_head work_exited; /* all we need is ->next == NULL */ 
 * 0 if succeeds or -ESRCH.

 */

int

task_work_add(struct task_struct *task, struct callback_head *work, bool notify)

task_work_add(struct task_struct *task, struct callback_head *work, int notify)

{

	struct callback_head *head;

	unsigned long flags;



	do {

		head = READ_ONCE(task->task_works);
@@ -36,8 +37,19 @@ task_work_add(struct task_struct *task, struct callback_head *work, bool notify) 
		work->next = head;

	} while (cmpxchg(&task->task_works, head, work) != head);



	if (notify)

	switch (notify) {

	case TWA_RESUME:

		set_notify_resume(task);

		break;

	case TWA_SIGNAL:

		if (lock_task_sighand(task, &flags)) {

			task->jobctl |= JOBCTL_TASK_WORK;

			signal_wake_up(task, 0);

			unlock_task_sighand(task, &flags);

		}

		break;

	}



	return 0;

}

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