Hi Linus, On Tue, 07 Sep 2021 12:22:37 +0100, Linus Walleij <linus.walleij@xxxxxxxxxx> wrote: > > On Wed, Aug 18, 2021 at 1:47 PM Pali Rohár <pali@xxxxxxxxxx> wrote: > > > I do not see any entry in MAINTAINERS file for pci-ftpci100.c driver, so > > I'm not sure to whom should I address this issue... > > It's me. > > > During pci-aardvark review, Marc pointed one issue which is currently > > available also in pci-ftpci100.c driver. > > > > When masking or unmasking interrupts there is read-modify-write sequence > > for FARADAY_PCI_CTRL2 register without any locking and is not atomic: > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/controller/pci-ftpci100.c?h=v5.13#n270 > > > > So there is race condition when masking/unmasking more interrupts at the > > same time. > > I thought those operations were called in atomic context. > How did you fix it? They are. But that doesn't mean that you cannot have two CPUs dealing with two different interrupts at the same time (using disable_irq(), for example). When that happens, your interrupt masking becomes a bit soup. irq_ack() also gets in the way, as it does a RMW of the same register. If the underlying HW is strictly UP, you're safe. But even in this case, you could have some locking that gets elided at compile time. I also don't understand why you always clear the interrupt status every time you mask/unmask an interrupt. I came up with the following patchlet, which is completely untested (not even compile-tested). Thanks, M. diff --git a/drivers/pci/controller/pci-ftpci100.c b/drivers/pci/controller/pci-ftpci100.c index 88980a44461d..dd1697e61206 100644 --- a/drivers/pci/controller/pci-ftpci100.c +++ b/drivers/pci/controller/pci-ftpci100.c @@ -120,6 +120,7 @@ struct faraday_pci_variant { }; struct faraday_pci { + raw_spinlock_t lock struct device *dev; void __iomem *base; struct irq_domain *irqdomain; @@ -270,34 +271,41 @@ static struct pci_ops faraday_pci_ops = { static void faraday_pci_ack_irq(struct irq_data *d) { struct faraday_pci *p = irq_data_get_irq_chip_data(d); + unsigned long flags; unsigned int reg; + raw_spin_lock_irqsave(&p->lock, flags); faraday_raw_pci_read_config(p, 0, 0, FARADAY_PCI_CTRL2, 4, ®); reg &= ~(0xF << PCI_CTRL2_INTSTS_SHIFT); reg |= BIT(irqd_to_hwirq(d) + PCI_CTRL2_INTSTS_SHIFT); faraday_raw_pci_write_config(p, 0, 0, FARADAY_PCI_CTRL2, 4, reg); + raw_spin_unlock_irqrestore(&p->lock, flags); } static void faraday_pci_mask_irq(struct irq_data *d) { struct faraday_pci *p = irq_data_get_irq_chip_data(d); + unsigned long flags; unsigned int reg; + raw_spin_lock_irqsave(&p->lock, flags); faraday_raw_pci_read_config(p, 0, 0, FARADAY_PCI_CTRL2, 4, ®); - reg &= ~((0xF << PCI_CTRL2_INTSTS_SHIFT) - | BIT(irqd_to_hwirq(d) + PCI_CTRL2_INTMASK_SHIFT)); + reg &= ~BIT(irqd_to_hwirq(d) + PCI_CTRL2_INTMASK_SHIFT); faraday_raw_pci_write_config(p, 0, 0, FARADAY_PCI_CTRL2, 4, reg); + raw_spin_unlock_irqrestore(&p->lock, flags); } static void faraday_pci_unmask_irq(struct irq_data *d) { struct faraday_pci *p = irq_data_get_irq_chip_data(d); + unsigned long flags; unsigned int reg; + raw_spin_lock_irqsave(&p->lock, flags); faraday_raw_pci_read_config(p, 0, 0, FARADAY_PCI_CTRL2, 4, ®); - reg &= ~(0xF << PCI_CTRL2_INTSTS_SHIFT); reg |= BIT(irqd_to_hwirq(d) + PCI_CTRL2_INTMASK_SHIFT); faraday_raw_pci_write_config(p, 0, 0, FARADAY_PCI_CTRL2, 4, reg); + raw_spin_unlock_irqrestore(&p->lock, flags); } static void faraday_pci_irq_handler(struct irq_desc *desc) @@ -441,6 +449,8 @@ static int faraday_pci_probe(struct platform_device *pdev) host->sysdata = p; p->dev = dev; + raw_spin_lock_init(&p->lock); + /* Retrieve and enable optional clocks */ clk = devm_clk_get(dev, "PCLK"); if (IS_ERR(clk)) -- Without deviation from the norm, progress is not possible.
