linux-kernel - Re: [PATCH] net: cadence: macb: Fix a possible deadlock in macb_halt

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Message-ID: <14c78296-97a0-46b4-b2aa-0ac8fa026d59@redhat.com>
Date: Thu, 8 May 2025 12:41:45 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Mathieu Othacehe <othacehe@....org>,
 Nicolas Ferre <nicolas.ferre@...rochip.com>
Cc: Claudiu Beznea <claudiu.beznea@...on.dev>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, anton.reding@...disgyr.com
Subject: Re: [PATCH] net: cadence: macb: Fix a possible deadlock in
 macb_halt_tx.

On 5/7/25 12:12 PM, Mathieu Othacehe wrote:
> There is a situation where after THALT is set high, TGO stays high as
> well. Because jiffies are never updated, as we are in a context with
> interrupts disabled, we never exit that loop and have a deadlock.
> 
> That deadlock was noticed on a sama5d4 device that stayed locked for days.
> 
> Use retries instead of jiffies so that the timeout really works and we do
> not have a deadlock anymore.
> 
> Signed-off-by: Mathieu Othacehe <othacehe@....org>

This looks like a fix that should target the net tree and include a
fixes tag, see Documentation/process/maintainer-netdev.rst

> ---
>  drivers/net/ethernet/cadence/macb_main.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> index 1fe8ec37491b1..ffcf569c14f6a 100644
> --- a/drivers/net/ethernet/cadence/macb_main.c
> +++ b/drivers/net/ethernet/cadence/macb_main.c
> @@ -997,20 +997,19 @@ static void macb_update_stats(struct macb *bp)
>  
>  static int macb_halt_tx(struct macb *bp)
>  {
> -	unsigned long	halt_time, timeout;
> -	u32		status;
> +	unsigned int delay_us = 250;
> +	unsigned int retries = MACB_HALT_TIMEOUT / delay_us;
> +	u32 status;
>  
>  	macb_writel(bp, NCR, macb_readl(bp, NCR) | MACB_BIT(THALT));
>  
> -	timeout = jiffies + usecs_to_jiffies(MACB_HALT_TIMEOUT);
>  	do {
> -		halt_time = jiffies;
>  		status = macb_readl(bp, TSR);
>  		if (!(status & MACB_BIT(TGO)))
>  			return 0;
>  
> -		udelay(250);
> -	} while (time_before(halt_time, timeout));
> +		udelay(delay_us);
> +	} while (retries-- > 0);

I think it would be better to use read_poll_timeout_atomic() instead of
sort-of open-codying it.

Thanks,

Paolo