linux-kernel - [tip: sched/core] sched: Unbreak wakeups

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Date:   Fri, 18 Jun 2021 11:24:05 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Davidlohr Bueso <dbueso@...e.de>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Will Deacon <will@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched: Unbreak wakeups

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     37aadc687ab441bbcb693ddae613acf9afcea1ab
Gitweb:        https://git.kernel.org/tip/37aadc687ab441bbcb693ddae613acf9afcea1ab
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Fri, 11 Jun 2021 10:28:11 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Fri, 18 Jun 2021 11:43:06 +02:00

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@...radead.org>
Reviewed-by: Davidlohr Bueso <dbueso@...e.de>
Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Acked-by: Will Deacon <will@...nel.org>
Link: https://lore.kernel.org/r/20210611082838.160855222@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(-)

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