diff mbox series

[1/6] sched: Unbreak wakeups

Message ID 20210602133040.271625424@infradead.org
State New
Headers show
Series sched: Cleanup task_struct::state | expand

Commit Message

Peter Zijlstra June 2, 2021, 1:12 p.m. UTC 
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();          ,-----> ,' (OoO load, observed !COND)
                             |       |
	                     |       |	COND = 1;
			     |	     `- if (t->state != RUNNING)
                             |		  wake_up_process(t); // not done
	  if (COND) ---------'
	    break;
	  schedule(); // forever waiting
	}
	t->state = TASK_RUNNING;

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 drivers/net/ethernet/qualcomm/qca_spi.c |    6 ++----
 drivers/usb/gadget/udc/max3420_udc.c    |   15 +++++----------
 drivers/usb/host/max3421-hcd.c          |    3 +--
 kernel/softirq.c                        |    2 +-
 4 files changed, 9 insertions(+), 17 deletions(-)

Comments

Greg Kroah-Hartman June 2, 2021, 1:58 p.m. UTC | #1 
On Wed, Jun 02, 2021 at 03:12:26PM +0200, Peter Zijlstra wrote:
> 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();          ,-----> ,' (OoO load, observed !COND)
>                              |       |
> 	                     |       |	COND = 1;
> 			     |	     `- if (t->state != RUNNING)
>                              |		  wake_up_process(t); // not done
> 	  if (COND) ---------'
> 	    break;
> 	  schedule(); // forever waiting
> 	}
> 	t->state = TASK_RUNNING;
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  drivers/net/ethernet/qualcomm/qca_spi.c |    6 ++----
>  drivers/usb/gadget/udc/max3420_udc.c    |   15 +++++----------
>  drivers/usb/host/max3421-hcd.c          |    3 +--
>  kernel/softirq.c                        |    2 +-
>  4 files changed, 9 insertions(+), 17 deletions(-)

For USB stuff:

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff mbox series

Patch

--- a/drivers/net/ethernet/qualcomm/qca_spi.c
+++ b/drivers/net/ethernet/qualcomm/qca_spi.c
@@ -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,
 
 	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;
--- a/drivers/usb/gadget/udc/max3420_udc.c
+++ b/drivers/usb/gadget/udc/max3420_udc.c
@@ -509,8 +509,7 @@  static irqreturn_t max3420_vbus_handler(
 			     ? 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(i
 	}
 	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_gad
 
 	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_
 	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_g
 	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;
--- a/drivers/usb/host/max3421-hcd.c
+++ b/drivers/usb/host/max3421-hcd.c
@@ -1169,8 +1169,7 @@  max3421_irq_handler(int irq, void *dev_i
 	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);
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -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);
 }