Re: [PATCH] PCI: uniphier: Serialize INTx masking/unmasking

On Wed, 25 Aug 2021 01:01:08 +0100,
Kunihiko Hayashi [off-list ref] wrote:

Hi Marc,

On 2021/08/24 1:57, Marc Zyngier wrote:

quoted

On Mon, 23 Aug 2021 16:09:27 +0100,
Pali Rohár [off-list ref] wrote:

quoted

+ Marc (who originally reported this issue)

On Monday 23 August 2021 20:18:20 Kunihiko Hayashi wrote:

quoted

The condition register PCI_RCV_INTX is used in irq_mask(), irq_unmask()
and irq_ack() callbacks. Accesses to register can occur at the same time
without a lock.
Add a lock into each callback to prevent the issue.

Fixes: 7e6d5cd88a6f ("PCI: uniphier: Add UniPhier PCIe host controller support")
Suggested-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>

Acked-by: Pali Rohár <pali@kernel.org>

quoted

---
  drivers/pci/controller/dwc/pcie-uniphier.c | 15 +++++++++++++++
  1 file changed, 15 insertions(+)

The previous patch is as follows:
https://lore.kernel.org/linux-pci/1629370566-29984-1-git-send-email-hayashi.kunihiko@socionext.com/ (local)

Changes in the previous patch:
- Change the subject and commit message

diff --git a/drivers/pci/controller/dwc/pcie-uniphier.c b/drivers/pci/controller/dwc/pcie-uniphier.c
index ebe43e9..5075714 100644
--- a/drivers/pci/controller/dwc/pcie-uniphier.c
+++ b/drivers/pci/controller/dwc/pcie-uniphier.c

@@ -186,12 +186,17 @@ static void uniphier_pcie_irq_ack(struct irq_data *d)
  	struct pcie_port *pp = irq_data_get_irq_chip_data(d);
  	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
  	struct uniphier_pcie_priv *priv = to_uniphier_pcie(pci);
+	unsigned long flags;
  	u32 val;
  +	raw_spin_lock_irqsave(&pp->lock, flags);
+
  	val = readl(priv->base + PCL_RCV_INTX);
  	val &= ~PCL_RCV_INTX_ALL_STATUS;
  	val |= BIT(irqd_to_hwirq(d) + PCL_RCV_INTX_STATUS_SHIFT);
  	writel(val, priv->base + PCL_RCV_INTX);
+
+	raw_spin_unlock_irqrestore(&pp->lock, flags);
  }
    static void uniphier_pcie_irq_mask(struct irq_data *d)

@@ -199,12 +204,17 @@ static void uniphier_pcie_irq_mask(struct irq_data *d)
  	struct pcie_port *pp = irq_data_get_irq_chip_data(d);
  	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
  	struct uniphier_pcie_priv *priv = to_uniphier_pcie(pci);
+	unsigned long flags;
  	u32 val;
  +	raw_spin_lock_irqsave(&pp->lock, flags);
+
  	val = readl(priv->base + PCL_RCV_INTX);
  	val &= ~PCL_RCV_INTX_ALL_MASK;
  	val |= BIT(irqd_to_hwirq(d) + PCL_RCV_INTX_MASK_SHIFT);

This looks extremely suspicious. You clear all the INTX mask bits, and
only set the one you need. How about the pre-existing bits?

Thanks for pointing out. No need to clear all INTX mask bits.
The pre-existing bits should be preserved.

quoted

quoted

quoted

  	writel(val, priv->base + PCL_RCV_INTX);
+
+	raw_spin_unlock_irqrestore(&pp->lock, flags);
  }
    static void uniphier_pcie_irq_unmask(struct irq_data *d)

@@ -212,12 +222,17 @@ static void uniphier_pcie_irq_unmask(struct irq_data *d)
  	struct pcie_port *pp = irq_data_get_irq_chip_data(d);
  	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
  	struct uniphier_pcie_priv *priv = to_uniphier_pcie(pci);
+	unsigned long flags;
  	u32 val;
  +	raw_spin_lock_irqsave(&pp->lock, flags);
+
  	val = readl(priv->base + PCL_RCV_INTX);
  	val &= ~PCL_RCV_INTX_ALL_MASK;
  	val &= ~BIT(irqd_to_hwirq(d) + PCL_RCV_INTX_MASK_SHIFT);

And by the same token, this second line is totally useless.

I think masking/unmasking is broken in this driver, locking or not.

Yes, this second line should be removed, too.

You mean the *first* line, right? The one clearing all the INTx
bits. If you remove the second line, you won't fix anything.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

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