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Date: Mon, 12 Mar 2007 22:12:43 +0300
From: Sergei Shtylyov <sshtylyov@...mvista.com>
To: Mark Brown <broonie@...ena.org.uk>
Cc: Mark Huth <mhuth@...sta.com>, jgarzik@...ox.com,
netdev@...r.kernel.org
Subject: Re: [PATCH] natsemi: netpoll fixes
Hello, I wrote:
>> Subject: natsemi: Fix NAPI for interrupt sharing
>> To: Jeff Garzik <jeff@...zik.org>
>> Cc: Sergei Shtylyov <sshtylyov@...mvista.com>, Simon Blake
>> <simon@...ylink.co.nz>, John Philips <johnphilips42@...oo.com>,
>> netdev@...r.kernel.org
>> The interrupt status register for the natsemi chips is clear on read and
>> was read unconditionally from both the interrupt and from the NAPI poll
>> routine, meaning that if the interrupt service routine was called (for
>> example, due to a shared interrupt) while a NAPI poll was scheduled
>> interrupts could be missed. This patch fixes that by ensuring that the
>> interrupt status register is only read when there is no poll scheduled.
>> It also reverts a workaround for this problem from the netpoll hook.
>> Thanks to Sergei Shtylyov <sshtylyov@...mvista.com> for spotting the
Well, I've blithely overlooked it, and it's you who did spot it. :-)
>> issue and Simon Blake <simon@...ylink.co.nz> for testing resources.
> Thanks for the patch!
> (If I only knew somebody else was working on that issue, it could
> have saved my cycles, sigh... but well, I should have said that I was
> going to recast the patch. :-)
>> Signed-Off-By: Mark Brown <broonie@...ena.org.uk>
>> Index: linux-2.6/drivers/net/natsemi.c
>> ===================================================================
>> --- linux-2.6.orig/drivers/net/natsemi.c 2007-03-11
>> 02:32:43.000000000 +0000
>> +++ linux-2.6/drivers/net/natsemi.c 2007-03-11 12:09:14.000000000
>> +0000
>> @@ -571,6 +571,8 @@
>> int oom;
>> /* Interrupt status */
>> u32 intr_status;
>> + int poll_active;
>> + spinlock_t intr_lock;
>> /* Do not touch the nic registers */
>> int hands_off;
>> /* Don't pay attention to the reported link state. */
>> @@ -812,9 +814,11 @@
>> pci_set_drvdata(pdev, dev);
>> np->iosize = iosize;
>> spin_lock_init(&np->lock);
>> + spin_lock_init(&np->intr_lock);
>> np->msg_enable = (debug >= 0) ? (1<<debug)-1 : NATSEMI_DEF_MSG;
>> np->hands_off = 0;
>> np->intr_status = 0;
>> + np->poll_active = 0;
>> np->eeprom_size = natsemi_pci_info[chip_idx].eeprom_size;
>> if (natsemi_pci_info[chip_idx].flags & NATSEMI_FLAG_IGNORE_PHY)
>> np->ignore_phy = 1;
>> @@ -1406,6 +1410,8 @@
>> writel(rfcr, ioaddr + RxFilterAddr);
>> }
>>
>> +/* MUST be called so that both NAPI poll and ISR are excluded due to
>> + * use of intr_status. */
>> static void reset_rx(struct net_device *dev)
>> {
>> int i;
>> @@ -2118,30 +2124,45 @@
>> struct net_device *dev = dev_instance;
>> struct netdev_private *np = netdev_priv(dev);
>> void __iomem * ioaddr = ns_ioaddr(dev);
>> + unsigned long flags;
>> + irqreturn_t status = IRQ_NONE;
>>
>> if (np->hands_off)
>> return IRQ_NONE;
>>
>> - /* Reading automatically acknowledges. */
>> - np->intr_status = readl(ioaddr + IntrStatus);
>> -
>> - if (netif_msg_intr(np))
>> - printk(KERN_DEBUG
>> - "%s: Interrupt, status %#08x, mask %#08x.\n",
>> - dev->name, np->intr_status,
>> - readl(ioaddr + IntrMask));
>> + spin_lock_irqsave(&np->intr_lock, flags);
> Yeah, I've suspected that we need to grab np->lock here... but does
> that separate spinlock actually protect us from anything?
I'm also not sure that we need to disable interrupts here.
>> - if (!np->intr_status)
>> - return IRQ_NONE;
>> + /* Reading IntrStatus automatically acknowledges so don't do
>> + * that while a poll is scheduled. */
>> + if (!np->poll_active) {
>> + np->intr_status = readl(ioaddr + IntrStatus);
>>
>> - prefetch(&np->rx_skbuff[np->cur_rx % RX_RING_SIZE]);
>> + if (netif_msg_intr(np))
>> + printk(KERN_DEBUG
>> + "%s: Interrupt, status %#08x, mask %#08x.\n",
>> + dev->name, np->intr_status,
>> + readl(ioaddr + IntrMask));
>> +
>> + if (np->intr_status) {
>> + prefetch(&np->rx_skbuff[np->cur_rx % RX_RING_SIZE]);
>> +
>> + /* Disable interrupts and register for poll */
>> + if (netif_rx_schedule_prep(dev)) {
>> + natsemi_irq_disable(dev);
>> + __netif_rx_schedule(dev);
>> + np->poll_active = 1;
>> + } else
>> + printk(KERN_WARNING
>> + "%s: Ignoring interrupt, status %#08x,
>> mask %#08x.\n",
>> + dev->name, np->intr_status,
>> + readl(ioaddr + IntrMask));
>>
>> - if (netif_rx_schedule_prep(dev)) {
>> - /* Disable interrupts and register for poll */
>> - natsemi_irq_disable(dev);
>> - __netif_rx_schedule(dev);
>> + status = IRQ_HANDLED;
>> + }
>> }
>> - return IRQ_HANDLED;
>> +
>> + spin_unlock_irqrestore(&np->intr_lock, flags);
>> + return status;
>> }
>>
>> /* This is the NAPI poll routine. As well as the standard RX handling
>> @@ -2154,8 +2175,15 @@
>>
>> int work_to_do = min(*budget, dev->quota);
>> int work_done = 0;
>> + unsigned long flags;
>>
>> do {
>> + if (netif_msg_intr(np))
>> + printk(KERN_DEBUG
>> + "%s: Poll, status %#08x, mask %#08x.\n",
>> + dev->name, np->intr_status,
>> + readl(ioaddr + IntrMask));
>> +
>> if (np->intr_status &
>> (IntrTxDone | IntrTxIntr | IntrTxIdle | IntrTxErr)) {
>> spin_lock(&np->lock);
>> @@ -2182,14 +2210,19 @@
>> np->intr_status = readl(ioaddr + IntrStatus);
>> } while (np->intr_status);
>>
>> + /* We need to ensure that the ISR doesn't run between telling
>> + * NAPI we're done and enabling the interrupt. */
> Why? :-O
Ah, got it: intr_handler() may disable interrupts (if some have appeared
since the last IntrStatus read) and upon return poll() will erroneously
re-enable them again... Good catch! :-)
Could also been dealt with by checking if the interrupt is actually
enabled in intr_handler() -- so, this would now seem a better solution to me
as we don't have to introduce flags/spinlocks, and avoid interrupt-off latency...
>> + spin_lock_irqsave(&np->intr_lock, flags);
>> +
>> netif_rx_complete(dev);
>> + np->poll_active = 0;
>>
>> /* Reenable interrupts providing nothing is trying to shut
>> * the chip down. */
>> - spin_lock(&np->lock);
>> - if (!np->hands_off && netif_running(dev))
>> + if (!np->hands_off)
>> natsemi_irq_enable(dev);
>> - spin_unlock(&np->lock);
>> +
>> + spin_unlock_irqrestore(&np->intr_lock, flags);
Not really sure we can replace one spinlock with another...
>> return 0;
>> }
WBR, Sergei
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