Commit 37aadc68 authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

sched: Unbreak wakeups 



Remove broken task->state references and let wake_up_process() DTRT.

The anti-pattern in these patches breaks the ordering of ->state vs
COND as described in the comment near set_current_state() and can lead
to missed wakeups:

	(OoO load, observes RUNNING)<-.
	for (;;) {                    |
	  t->state = UNINTERRUPTIBLE; |
	  smp_mb();          ,----->  | (observes !COND)
                             |        /
	  if (COND) ---------'       |	COND = 1;
		break;		     `- if (t->state != RUNNING)
					  wake_up_process(t); // not done
	  schedule(); // forever waiting
	}
	t->state = TASK_RUNNING;

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarDavidlohr Bueso <dbueso@suse.de>
Acked-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: default avatarWill Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20210611082838.160855222@infradead.org
parent b2c0931a

drivers/net/ethernet/qualcomm/qca_spi.c

+2 −4
Original line number Diff line number Diff line
@@ -653,8 +653,7 @@ qcaspi_intr_handler(int irq, void *data) 
	struct qcaspi *qca = data;



	qca->intr_req++;

	if (qca->spi_thread &&

	    qca->spi_thread->state != TASK_RUNNING)

	if (qca->spi_thread)

		wake_up_process(qca->spi_thread);



	return IRQ_HANDLED;
@@ -777,8 +776,7 @@ qcaspi_netdev_xmit(struct sk_buff *skb, struct net_device *dev) 


	netif_trans_update(dev);



	if (qca->spi_thread &&

	    qca->spi_thread->state != TASK_RUNNING)

	if (qca->spi_thread)

		wake_up_process(qca->spi_thread);



	return NETDEV_TX_OK;

drivers/usb/gadget/udc/max3420_udc.c

+5 −10
Original line number Diff line number Diff line
@@ -509,8 +509,7 @@ static irqreturn_t max3420_vbus_handler(int irq, void *dev_id) 
			     ? USB_STATE_POWERED : USB_STATE_NOTATTACHED);

	spin_unlock_irqrestore(&udc->lock, flags);



	if (udc->thread_task &&

	    udc->thread_task->state != TASK_RUNNING)

	if (udc->thread_task)

		wake_up_process(udc->thread_task);



	return IRQ_HANDLED;
@@ -529,8 +528,7 @@ static irqreturn_t max3420_irq_handler(int irq, void *dev_id) 
	}

	spin_unlock_irqrestore(&udc->lock, flags);



	if (udc->thread_task &&

	    udc->thread_task->state != TASK_RUNNING)

	if (udc->thread_task)

		wake_up_process(udc->thread_task);



	return IRQ_HANDLED;
@@ -1093,8 +1091,7 @@ static int max3420_wakeup(struct usb_gadget *gadget) 


	spin_unlock_irqrestore(&udc->lock, flags);



	if (udc->thread_task &&

	    udc->thread_task->state != TASK_RUNNING)

	if (udc->thread_task)

		wake_up_process(udc->thread_task);

	return ret;

}
@@ -1117,8 +1114,7 @@ static int max3420_udc_start(struct usb_gadget *gadget, 
	udc->todo |= UDC_START;

	spin_unlock_irqrestore(&udc->lock, flags);



	if (udc->thread_task &&

	    udc->thread_task->state != TASK_RUNNING)

	if (udc->thread_task)

		wake_up_process(udc->thread_task);



	return 0;
@@ -1137,8 +1133,7 @@ static int max3420_udc_stop(struct usb_gadget *gadget) 
	udc->todo |= UDC_START;

	spin_unlock_irqrestore(&udc->lock, flags);



	if (udc->thread_task &&

	    udc->thread_task->state != TASK_RUNNING)

	if (udc->thread_task)

		wake_up_process(udc->thread_task);



	return 0;

drivers/usb/host/max3421-hcd.c

+1 −2
Original line number Diff line number Diff line
@@ -1169,8 +1169,7 @@ max3421_irq_handler(int irq, void *dev_id) 
	struct spi_device *spi = to_spi_device(hcd->self.controller);

	struct max3421_hcd *max3421_hcd = hcd_to_max3421(hcd);



	if (max3421_hcd->spi_thread &&

	    max3421_hcd->spi_thread->state != TASK_RUNNING)

	if (max3421_hcd->spi_thread)

		wake_up_process(max3421_hcd->spi_thread);

	if (!test_and_set_bit(ENABLE_IRQ, &max3421_hcd->todo))

		disable_irq_nosync(spi->irq);

kernel/softirq.c

+1 −1
Original line number Diff line number Diff line
@@ -76,7 +76,7 @@ static void wakeup_softirqd(void) 
	/* Interrupts are disabled: no need to stop preemption */

	struct task_struct *tsk = __this_cpu_read(ksoftirqd);



	if (tsk && tsk->state != TASK_RUNNING)

	if (tsk)

		wake_up_process(tsk);

}