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: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

2 files changed, 21 insertions, 5 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index 5ca48cc5da76..ee22ec78fd6d 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -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
diff --git a/kernel/task_work.c b/kernel/task_work.c
index 825f28259a19..5c0848ca1287 100644
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -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;
 }