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

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Message-ID: <f4d13190-facf-55ca-58c5-cd0d68e377d7@socionext.com>
Date:   Wed, 25 Aug 2021 09:01:08 +0900
From:   Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
To:     Marc Zyngier <maz@...nel.org>,
        Pali Rohár <pali@...nel.org>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: uniphier: Serialize INTx masking/unmasking

Hi Marc,

On 2021/08/24 1:57, Marc Zyngier wrote:
> On Mon, 23 Aug 2021 16:09:27 +0100,
> Pali Rohár <pali@...nel.org> wrote:
>>
>> + Marc (who originally reported this issue)
>>
>> On Monday 23 August 2021 20:18:20 Kunihiko Hayashi wrote:
>>> 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@...nel.org>
>>> Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
>>
>> Acked-by: Pali Rohár <pali@...nel.org>
>>
>>> ---
>>>   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/
>>>
>>> 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.

> 
>>>   	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.
I'll fix this bug and add mask locking.

Thank you,

---
Best Regards
Kunihiko Hayashi