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: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20210611082838.160855222@infradead.org

diff --git a/drivers/net/ethernet/qualcomm/qca_spi.c b/drivers/net/ethernet/qualcomm/qca_spi.c
index ab9b025..0a6b811 100644 (file)
--- 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, 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;

diff --git a/drivers/usb/gadget/udc/max3420_udc.c b/drivers/usb/gadget/udc/max3420_udc.c
index 3517954..34f4db5 100644 (file)
--- 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(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;

diff --git a/drivers/usb/host/max3421-hcd.c b/drivers/usb/host/max3421-hcd.c
index afd9174..e7a8e06 100644 (file)
--- 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_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);

diff --git a/kernel/softirq.c b/kernel/softirq.c
index 4992853..5ddc3b1 100644 (file)
--- 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);
 }