Subject: Re: [PATCH] Fix cpm uart corruption with PREEMPT_RT

From: Scott Wood <[email-masked]>
Date: Tue, 20 May 2008 14:33:08 -0500

On Tue, May 20, 2008 at 02:28:16PM -0500, Rune Torgersen wrote:
> Fix CPM serial port corruption when running with CONFIG_PREEMPT_RT.
> Userland usage of console, and kernel printf's were stepping on each others toes.
> 
> Signed-off-by: Rune Torgersen <[email-masked]>
> 
> diff --git a/drivers/serial/cpm_uart/cpm_uart_core.c b/drivers/serial/cpm_uart/cpm_uart_core.c
> index fb93403..79c109d 100755
> --- a/drivers/serial/cpm_uart/cpm_uart_core.c
> +++ b/drivers/serial/cpm_uart/cpm_uart_core.c
> @@ -1214,7 +1214,9 @@ static void cpm_uart_console_write(struct console *co, const char *s,
>  	unsigned int i;
>  	cbd_t __iomem *bdp, *bdbase;
>  	unsigned char *cp;
> +	unsigned long flags;
>  
> +	spin_lock_irqsave(&pinfo->port.lock, flags);
>  	/* Get the address of the host memory buffer.
>  	 */
>  	bdp = pinfo->tx_cur;
> @@ -1282,6 +1284,8 @@ static void cpm_uart_console_write(struct console *co, const char *s,
>  		;
>  
>  	pinfo->tx_cur = bdp;
> +
> +	spin_unlock_irqrestore(&pinfo->port.lock, flags);
>  }

We should bypass the lock when oops_in_progress is set, something like:

diff --git a/drivers/serial/cpm_uart/cpm_uart_core.c b/drivers/serial/cpm_uart/cpm_uart_core.c
index a19dc7e..bc45f8a 100644
--- a/drivers/serial/cpm_uart/cpm_uart_core.c
+++ b/drivers/serial/cpm_uart/cpm_uart_core.c
@@ -1178,6 +1178,14 @@ static void cpm_uart_console_write(struct console *co, const char *s,
 	unsigned int i;
 	cbd_t __iomem *bdp, *bdbase;
 	unsigned char *cp;
+	unsigned long flags;
+	int nolock = oops_in_progress;
+
+	if (unlikely(nolock)) {
+		local_irq_save(flags);
+	} else {
+		spin_lock_irqsave(&pinfo->port.lock, flags);
+	}
 
 	/* Get the address of the host memory buffer.
 	 */
@@ -1239,8 +1247,13 @@ static void cpm_uart_console_write(struct console *co, const char *s,
 		;
 
 	pinfo->tx_cur = bdp;
-}
 
+	if (unlikely(nolock)) {
+		local_irq_restore(flags);
+	} else {
+		spin_unlock_irqrestore(&pinfo->port.lock, flags);
+	}
+}
 
 static int __init cpm_uart_console_setup(struct console *co, char *options)
 {

-Scott