linux-kernel - [PATCH LINUX v4 12/13] tty: xuartps: Improve sysrq handling

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Date:	Sat, 5 Dec 2015 20:39:28 -0800
From:	Soren Brinkmann <soren.brinkmann@...inx.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>
CC:	Michal Simek <michal.simek@...inx.com>,
	<linux-serial@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>,
	"Peter Hurley" <peter@...leysoftware.com>,
	Moritz Fischer <moritz.fischer@...us.com>,
	Soren Brinkmann <soren.brinkmann@...inx.com>
Subject: [PATCH LINUX v4 12/13] tty: xuartps: Improve sysrq handling

Handling magic sysrq included dropping a lock to avoid a deadlock that
happened when cdns_uart_console_write tried to acquire a lock in the
from the sysrq code path. By making the acquisition of the lock in
cdns_uart_console_write depending on port->sysrq, cdns_uart_handle_rx can be
simplified to simply call uart_handle_sysrq.

Suggested-by: Peter Hurley <peter@...leysoftware.com>
Signed-off-by: Soren Brinkmann <soren.brinkmann@...inx.com>
---
v4:
 - added this patch
---
 drivers/tty/serial/xilinx_uartps.c | 20 +++++---------------
 1 file changed, 5 insertions(+), 15 deletions(-)

diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
index 7afab0c36528..3b8d15fa5959 100644
--- a/drivers/tty/serial/xilinx_uartps.c
+++ b/drivers/tty/serial/xilinx_uartps.c
@@ -221,20 +221,8 @@ static void cdns_uart_handle_rx(struct uart_port *port, unsigned int isrstatus)
 				continue;
 		}
 
-#ifdef SUPPORT_SYSRQ
-		/*
-		 * uart_handle_sysrq_char() doesn't work if
-		 * spinlocked, for some reason
-		 */
-		 if (port->sysrq) {
-			spin_unlock(&port->lock);
-			if (uart_handle_sysrq_char(port, data)) {
-				spin_lock(&port->lock);
-				continue;
-			}
-			spin_lock(&port->lock);
-		}
-#endif
+		if (uart_handle_sysrq_char(port, data))
+			continue;
 
 		port->icount.rx++;
 
@@ -1121,7 +1109,9 @@ static void cdns_uart_console_write(struct console *co, const char *s,
 	unsigned int imr, ctrl;
 	int locked = 1;
 
-	if (oops_in_progress)
+	if (port->sysrq)
+		locked = 0;
+	else if (oops_in_progress)
 		locked = spin_trylock_irqsave(&port->lock, flags);
 	else
 		spin_lock_irqsave(&port->lock, flags);
-- 
2.6.3.3.g9bb996a

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