linux-kernel - Re: [PATCH] serial: mxs-auart: add spinlock around changing cts state

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Message-ID: <ZfihlNj1qMm1aJvI@lizhi-Precision-Tower-5810>
Date: Mon, 18 Mar 2024 16:18:28 -0400
From: Frank Li <Frank.li@....com>
To: Emil Kronborg <emil.kronborg@...tonmail.com>
Cc: jirislaby@...nel.org, gregkh@...uxfoundation.org,
	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, imx@...ts.linux.dev
Subject: Re: [PATCH] serial: mxs-auart: add spinlock around changing cts state

On Fri, Mar 15, 2024 at 03:42:29PM +0000, Emil Kronborg wrote:
> The uart_handle_cts_change() function in serial_core expects the caller
> to hold uport->lock. For example, I have seen the below kernel splat,
> when the Bluetooth driver is loaded on an i.MX28 board.
> 
>     [   85.119255] ------------[ cut here ]------------
>     [   85.124413] WARNING: CPU: 0 PID: 27 at /drivers/tty/serial/serial_core.c:3453 uart_handle_cts_change+0xb4/0xec

Add:  mxs_auart_modem_status()
      mxs_auart_irq_handle()

May help understand why need add lock in mxs_auart_irq_handle().
          
>     [   85.134694] Modules linked in: hci_uart bluetooth ecdh_generic ecc wlcore_sdio configfs
>     [   85.143314] CPU: 0 PID: 27 Comm: kworker/u3:0 Not tainted 6.6.3-00021-gd62a2f068f92 #1
>     [   85.151396] Hardware name: Freescale MXS (Device Tree)
>     [   85.156679] Workqueue: hci0 hci_power_on [bluetooth]
>     [   85.164243]  unwind_backtrace from show_stack+0x10/0x14
>     (...)
> 
> Signed-off-by: Emil Kronborg <emil.kronborg@...tonmail.com>

Cc stable and add fix tag

Frank

> ---
>  drivers/tty/serial/mxs-auart.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/serial/mxs-auart.c b/drivers/tty/serial/mxs-auart.c
> index 4749331fe618..1e8853eae504 100644
> --- a/drivers/tty/serial/mxs-auart.c
> +++ b/drivers/tty/serial/mxs-auart.c
> @@ -1086,11 +1086,13 @@ static void mxs_auart_set_ldisc(struct uart_port *port,
>  
>  static irqreturn_t mxs_auart_irq_handle(int irq, void *context)
>  {
> -	u32 istat;
> +	u32 istat, stat;
>  	struct mxs_auart_port *s = context;
>  	u32 mctrl_temp = s->mctrl_prev;
> -	u32 stat = mxs_read(s, REG_STAT);
>  
> +	uart_port_lock(&s->port);
> +
> +	stat = mxs_read(s, REG_STAT);
>  	istat = mxs_read(s, REG_INTR);
>  
>  	/* ack irq */
> @@ -1126,6 +1128,8 @@ static irqreturn_t mxs_auart_irq_handle(int irq, void *context)
>  		istat &= ~AUART_INTR_TXIS;
>  	}
>  
> +	uart_port_unlock(&s->port);
> +
>  	return IRQ_HANDLED;
>  }
>  
> -- 
> 2.44.0
> 
>