linux-kernel - Re: [PATCH v2 0/6] atmel_serial: Cleanups, irq handler splitup & DMA

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Date:	Wed, 19 Dec 2007 17:09:35 +0100
From:	Haavard Skinnemoen <hskinnemoen@...el.com>
To:	"Remy Bohmer" <linux@...mer.net>
Cc:	"Andrew Victor" <linux@...im.org.za>,
	linux-arm-kernel@...ts.arm.linux.org.uk,
	"Russell King" <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org, kernel@...32linux.org
Subject: Re: [PATCH v2 0/6] atmel_serial: Cleanups, irq handler splitup &
 DMA

On Wed, 19 Dec 2007 16:57:04 +0100
"Remy Bohmer" <linux@...mer.net> wrote:

> Hello Haavard,
> 
> Sorry.. But I get an Oops on Preempt-RT with the latest set of
> patches. I did not see it earlier today with the other set of patches.

Hmm...from the backtrace, it looks like lock recursion -- port->lock is
held for the whole duration of the tasklet, but we somehow end up in
uart_start(), which grabs the lock again.

Could you try the patch below? It's a bit strange that you got an oops
though...

Haavard

diff --git a/drivers/serial/atmel_serial.c b/drivers/serial/atmel_serial.c
index 7967054..948c643 100644
--- a/drivers/serial/atmel_serial.c
+++ b/drivers/serial/atmel_serial.c
@@ -666,7 +666,13 @@ static void atmel_rx_from_ring(struct uart_port *port)
 		uart_insert_char(port, status, ATMEL_US_OVRE, c.ch, flg);
 	}
 
+	/*
+	 * Drop the lock here since it might end up calling
+	 * uart_start(), which takes the lock.
+	 */
+	spin_unlock(&port->lock);
 	tty_flip_buffer_push(port->info->tty);
+	spin_lock(&port->lock);
 }
 
 static void atmel_rx_from_dma(struct uart_port *port)
--
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