Re: [PATCH v4 1/4] serial: sh-sci: Fix locking in sci_submit_rx()

From: Simon Horman <horms@verge.net.au>
To: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jslaby@suse.com>, Ulrich Hecht <uli+renesas@fpond.eu>,
	Wolfram Sang <wsa+renesas@sang-engineering.com>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	linux-renesas-soc@vger.kernel.org, linux-sh@vger.kernel.org,
	linux-serial@vger.kernel.org
Subject: Re: [PATCH v4 1/4] serial: sh-sci: Fix locking in sci_submit_rx()
Date: Mon, 17 Dec 2018 14:17:52 +0100	[thread overview]
Message-ID: <20181217131751.pyhstvri6yustm6v@verge.net.au> (raw)
In-Reply-To: <20181213184444.21904-2-geert+renesas@glider.be>

On Thu, Dec 13, 2018 at 07:44:41PM +0100, Geert Uytterhoeven wrote:
> Some callers of sci_submit_rx() hold the port spinlock, others don't.
> During fallback to PIO, the driver needs to obtain the port spinlock.
> If the lock was already held, spinlock recursion is detected, causing a
> deadlock: BUG: spinlock recursion on CPU#0.
> 
> Fix this by adding a flag parameter to sci_submit_rx() for the caller to
> indicate the port spinlock is already held, so spinlock recursion can be
> avoided.
> 
> Move the spin_lock_irqsave() up, so all DMA disable steps are protected,
> which is safe as the recently introduced dmaengine_terminate_async() can
> be called in atomic context.
> 
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

Reviewed-by: Simon Horman <horms+renesas@verge.net.au>

> ---
> v4:
>   - No changes,
> 
> v3:
>   - Split in multiple patches.
> ---
>  drivers/tty/serial/sh-sci.c | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
> index 8146d9cef0cbe2d0..2a08039f792235e5 100644
> --- a/drivers/tty/serial/sh-sci.c
> +++ b/drivers/tty/serial/sh-sci.c
> @@ -1331,7 +1331,7 @@ static void sci_tx_dma_release(struct sci_port *s)
>  	dma_release_channel(chan);
>  }
>  
> -static void sci_submit_rx(struct sci_port *s)
> +static void sci_submit_rx(struct sci_port *s, bool port_lock_held)
>  {
>  	struct dma_chan *chan = s->chan_rx;
>  	struct uart_port *port = &s->port;
> @@ -1362,16 +1362,18 @@ static void sci_submit_rx(struct sci_port *s)
>  	return;
>  
>  fail:
> +	/* Switch to PIO */
> +	if (!port_lock_held)
> +		spin_lock_irqsave(&port->lock, flags);
>  	if (i)
>  		dmaengine_terminate_async(chan);
>  	for (i = 0; i < 2; i++)
>  		s->cookie_rx[i] = -EINVAL;
>  	s->active_rx = -EINVAL;
> -	/* Switch to PIO */
> -	spin_lock_irqsave(&port->lock, flags);
>  	s->chan_rx = NULL;
>  	sci_start_rx(port);
> -	spin_unlock_irqrestore(&port->lock, flags);
> +	if (!port_lock_held)
> +		spin_unlock_irqrestore(&port->lock, flags);
>  }
>  
>  static void work_fn_tx(struct work_struct *work)
> @@ -1491,7 +1493,7 @@ static enum hrtimer_restart rx_timer_fn(struct hrtimer *t)
>  	}
>  
>  	if (port->type == PORT_SCIFA || port->type == PORT_SCIFB)
> -		sci_submit_rx(s);
> +		sci_submit_rx(s, true);
>  
>  	/* Direct new serial port interrupts back to CPU */
>  	scr = serial_port_in(port, SCSCR);
> @@ -1617,7 +1619,7 @@ static void sci_request_dma(struct uart_port *port)
>  		s->chan_rx_saved = s->chan_rx = chan;
>  
>  		if (port->type == PORT_SCIFA || port->type == PORT_SCIFB)
> -			sci_submit_rx(s);
> +			sci_submit_rx(s, false);
>  	}
>  }
>  
> @@ -1667,7 +1669,7 @@ static irqreturn_t sci_rx_interrupt(int irq, void *ptr)
>  			scr |= SCSCR_RDRQE;
>  		} else {
>  			scr &= ~SCSCR_RIE;
> -			sci_submit_rx(s);
> +			sci_submit_rx(s, false);
>  		}
>  		serial_port_out(port, SCSCR, scr);
>  		/* Clear current interrupt */
> -- 
> 2.17.1
>