From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexey Brodkin Subject: [PATCH] serial: 8250_port: Remove dangerous pr_debug() Date: Tue, 10 Jan 2017 18:11:29 +0300 Message-ID: <1484061089-20070-1-git-send-email-abrodkin@synopsys.com> Return-path: Sender: linux-kernel-owner@vger.kernel.org To: linux-serial@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Alexey Brodkin , Greg Kroah-Hartman , Jiri Slaby , Peter Hurley , Andy Shevchenko , Phillip Raffeck , Anton Wuerfel , "Matwey V. Kornilov" , Yegor Yefremov , Thor Thayer List-Id: linux-serial@vger.kernel.org With CONFIG_DYNAMIC_DEBUG if dyndbg enables debug output in 8250_port.c deadlock happens inevitably on UART IRQ handling. That's the problematic execution path: ---------------------------->8------------------------ UART IRQ: serial8250_interrupt() -> serial8250_handle_irq(): lock "port->lock" -> pr_debug() -> serial8250_console_write(): bump in locked "port->lock". OR (if above pr_debug() gets removed): serial8250_tx_chars() -> pr_debug() -> serial8250_console_write(): bump in locked "port->lock". ---------------------------->8------------------------ So let's get rid of those not that much useful debug entries. Discussed problem could be easily reproduced with QEMU for x86_64. As well as this fix could be mimicked with muting of dynamic debug for the problematic lines as simple as: ---------------------------->8------------------------ dyndbg="+p; file 8250_port.c line 1756 -p; file 8250_port.c line 1822 -p" ---------------------------->8------------------------ Signed-off-by: Alexey Brodkin Cc: Greg Kroah-Hartman Cc: Jiri Slaby Cc: Peter Hurley Cc: Andy Shevchenko Cc: Phillip Raffeck Cc: Anton Wuerfel Cc: "Matwey V. Kornilov" Cc: Yegor Yefremov Cc: Thor Thayer --- drivers/tty/serial/8250/8250_port.c | 4 ---- 1 file changed, 4 deletions(-) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index fe4399b41df6..3cfdd745a97a 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -1753,8 +1753,6 @@ void serial8250_tx_chars(struct uart_8250_port *up) if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS) uart_write_wakeup(port); - pr_debug("%s: THRE\n", __func__); - /* * With RPM enabled, we have to wait until the FIFO is empty before the * HW can go idle. So we get here once again with empty FIFO and disable @@ -1819,8 +1817,6 @@ int serial8250_handle_irq(struct uart_port *port, unsigned int iir) status = serial_port_in(port, UART_LSR); - pr_debug("%s: status = %x\n", __func__, status); - if (status & (UART_LSR_DR | UART_LSR_BI)) { if (!up->dma || handle_rx_dma(up, iir)) status = serial8250_rx_chars(up, status); -- 2.7.4