4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Alexey Brodkin <alexey.brod...@synopsys.com>
[ Upstream commit 699a11ba7ec869b006623182881f2f1f5b4aea53 ]
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 <abrod...@synopsys.com>
Cc: Jiri Slaby <jsl...@suse.com>
Cc: Peter Hurley <pe...@hurleysoftware.com>
Cc: Phillip Raffeck <phillip.raff...@fau.de>
Cc: Anton Wuerfel <anton.wuer...@fau.de>
Cc: "Matwey V. Kornilov" <mat...@sai.msu.ru>
Cc: Yegor Yefremov <yegorsli...@googlemail.com>
Cc: Thor Thayer <ttha...@opensource.altera.com>
Reviewed-by: Andy Shevchenko <andriy.shevche...@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Signed-off-by: Sasha Levin <alexander.le...@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
drivers/tty/serial/8250/8250_port.c | 4 ----
1 file changed, 4 deletions(-)
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1751,8 +1751,6 @@ void serial8250_tx_chars(struct uart_825
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
@@ -1817,8 +1815,6 @@ int serial8250_handle_irq(struct uart_po
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);
