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

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Date:   Wed, 25 Aug 2021 10:07:08 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
Cc:     Pali Rohár <pali@...nel.org>,
        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

On Wed, 25 Aug 2021 01:01:08 +0100,
Kunihiko Hayashi <hayashi.kunihiko@...ionext.com> wrote:
> 
> 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.

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.