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

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Date:   Mon, 23 Aug 2021 17:57:08 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Pali Rohár <pali@...nel.org>,
        Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
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

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?

> >  	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.

	M.

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