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@hurleysoftware.com>
Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
index 8014dd3..0eecba8 100644 (file)
--- a/drivers/tty/serial/xilinx_uartps.c
+++ b/drivers/tty/serial/xilinx_uartps.c
@@ -220,20 +220,8 @@ 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++;
 
@@ -1128,7 +1116,9 @@ 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);