* pci-ftpci100: race condition in masking/unmasking interrupts @ 2021-08-18 11:47 Pali Rohár 2021-09-07 11:22 ` Linus Walleij 0 siblings, 1 reply; 4+ messages in thread From: Pali Rohár @ 2021-08-18 11:47 UTC (permalink / raw) To: Linus Walleij, Lorenzo Pieralisi, Rob Herring Cc: Marc Zyngier, linux-pci, linux-kernel Hello! 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... 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. ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: pci-ftpci100: race condition in masking/unmasking interrupts 2021-08-18 11:47 pci-ftpci100: race condition in masking/unmasking interrupts Pali Rohár @ 2021-09-07 11:22 ` Linus Walleij 2021-09-07 12:20 ` Pali Rohár 2021-09-07 16:53 ` Marc Zyngier 0 siblings, 2 replies; 4+ messages in thread From: Linus Walleij @ 2021-09-07 11:22 UTC (permalink / raw) To: Pali Rohár Cc: Lorenzo Pieralisi, Rob Herring, Marc Zyngier, linux-pci, linux-kernel On Wed, Aug 18, 2021 at 1:47 PM Pali Rohár <pali@kernel.org> 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? Yours, Linus Walleij ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: pci-ftpci100: race condition in masking/unmasking interrupts 2021-09-07 11:22 ` Linus Walleij @ 2021-09-07 12:20 ` Pali Rohár 2021-09-07 16:53 ` Marc Zyngier 1 sibling, 0 replies; 4+ messages in thread From: Pali Rohár @ 2021-09-07 12:20 UTC (permalink / raw) To: Linus Walleij Cc: Lorenzo Pieralisi, Rob Herring, Marc Zyngier, linux-pci, linux-kernel On Tuesday 07 September 2021 13:22:37 Linus Walleij wrote: > On Wed, Aug 18, 2021 at 1:47 PM Pali Rohár <pali@kernel.org> 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. Ok! So could you send update for MAINTAINERS file for this driver? > > 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. I guess that they cannot be as for performance reasons you could want to mask or unmask more interrupts in parallel on more CPUs. > How did you fix it? Guarding all read-modify-write operations on register by raw spin lock. See: https://lore.kernel.org/linux-pci/20210820155020.3000-1-pali@kernel.org/ ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: pci-ftpci100: race condition in masking/unmasking interrupts 2021-09-07 11:22 ` Linus Walleij 2021-09-07 12:20 ` Pali Rohár @ 2021-09-07 16:53 ` Marc Zyngier 1 sibling, 0 replies; 4+ messages in thread From: Marc Zyngier @ 2021-09-07 16:53 UTC (permalink / raw) To: Linus Walleij Cc: Pali Rohár, Lorenzo Pieralisi, Rob Herring, linux-pci, linux-kernel Hi Linus, On Tue, 07 Sep 2021 12:22:37 +0100, Linus Walleij <linus.walleij@linaro.org> wrote: > > On Wed, Aug 18, 2021 at 1:47 PM Pali Rohár <pali@kernel.org> 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. ^ permalink raw reply related [flat|nested] 4+ messages in thread
end of thread, other threads:[~2021-09-07 16:54 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2021-08-18 11:47 pci-ftpci100: race condition in masking/unmasking interrupts Pali Rohár 2021-09-07 11:22 ` Linus Walleij 2021-09-07 12:20 ` Pali Rohár 2021-09-07 16:53 ` Marc Zyngier
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