netdev - Re: [PATCH net] net: ethernet: cortina: Locking fixes

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Message-ID: <Zj_fAddoi7wqHufL@qmqm.qmqm.pl>
Date: Sat, 11 May 2024 23:11:29 +0200
From: Michał Mirosław <mirq-linux@...e.qmqm.pl>
To: Linus Walleij <linus.walleij@...aro.org>
Cc: Hans Ulli Kroll <ulli.kroll@...glemail.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org
Subject: Re: [PATCH net] net: ethernet: cortina: Locking fixes

On Thu, May 09, 2024 at 09:44:54AM +0200, Linus Walleij wrote:
> This fixes a probably long standing problem in the Cortina
> Gemini ethernet driver: there are some paths in the code
> where the IRQ registers are written without taking the proper
> locks.
> 
> Fixes: 4d5ae32f5e1e ("net: ethernet: Add a driver for Gemini gigabit ethernet")
> Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
> ---
>  drivers/net/ethernet/cortina/gemini.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/cortina/gemini.c b/drivers/net/ethernet/cortina/gemini.c
> index 705c3eb19cd3..d1fbadbf86d4 100644
> --- a/drivers/net/ethernet/cortina/gemini.c
> +++ b/drivers/net/ethernet/cortina/gemini.c
> @@ -1107,10 +1107,13 @@ static void gmac_tx_irq_enable(struct net_device *netdev,
>  {
>  	struct gemini_ethernet_port *port = netdev_priv(netdev);
>  	struct gemini_ethernet *geth = port->geth;
> +	unsigned long flags;
>  	u32 val, mask;
>  
>  	netdev_dbg(netdev, "%s device %d\n", __func__, netdev->dev_id);
>  
> +	spin_lock_irqsave(&geth->irq_lock, flags);
> +
>  	mask = GMAC0_IRQ0_TXQ0_INTS << (6 * netdev->dev_id + txq);
>  
>  	if (en)
> @@ -1119,6 +1122,8 @@ static void gmac_tx_irq_enable(struct net_device *netdev,
>  	val = readl(geth->base + GLOBAL_INTERRUPT_ENABLE_0_REG);
>  	val = en ? val | mask : val & ~mask;
>  	writel(val, geth->base + GLOBAL_INTERRUPT_ENABLE_0_REG);
> +
> +	spin_unlock_irqrestore(&geth->irq_lock, flags);
>  }
>  

Looks good, though spinlock looks necessary only around the ENABLE0
rmw, as the 'if (en)' part is resetting the "triggered" flag of the
interrupt (acking earlier-ignored interrupts).

>  static void gmac_tx_irq(struct net_device *netdev, unsigned int txq_num)
> @@ -1415,15 +1420,19 @@ static unsigned int gmac_rx(struct net_device *netdev, unsigned int budget)
>  	union gmac_rxdesc_3 word3;
>  	struct page *page = NULL;
>  	unsigned int page_offs;
> +	unsigned long flags;
>  	unsigned short r, w;
>  	union dma_rwptr rw;
>  	dma_addr_t mapping;
>  	int frag_nr = 0;
>  
> +	spin_lock_irqsave(&geth->irq_lock, flags);
>  	rw.bits32 = readl(ptr_reg);
>  	/* Reset interrupt as all packages until here are taken into account */
>  	writel(DEFAULT_Q0_INT_BIT << netdev->dev_id,
>  	       geth->base + GLOBAL_INTERRUPT_STATUS_1_REG);
> +	spin_unlock_irqrestore(&geth->irq_lock, flags);
> +

This doesn't look right: one, those are different registers, two it is
an IRQ-acking write.  In this case it is important that readl() is ordered
before writel(), but the spinlock doesn't guarantee that.

> @@ -1726,10 +1735,9 @@ static irqreturn_t gmac_irq(int irq, void *data)
>  		gmac_update_hw_stats(netdev);
>  
>  	if (val & (GMAC0_RX_OVERRUN_INT_BIT << (netdev->dev_id * 8))) {
> +		spin_lock(&geth->irq_lock);
>  		writel(GMAC0_RXDERR_INT_BIT << (netdev->dev_id * 8),
>  		       geth->base + GLOBAL_INTERRUPT_STATUS_4_REG);
> -
> -		spin_lock(&geth->irq_lock);
>  		u64_stats_update_begin(&port->ir_stats_syncp);
>  		++port->stats.rx_fifo_errors;
>  		u64_stats_update_end(&port->ir_stats_syncp);

This, too, is a IRQ-acking write that doesn't seem to gain much by
running inside the spin-locked section.

Best Regards
Michał Mirosław