This is a note to let you know that I've just added the patch titled
serial: 8250_port: Remove dangerous pr_debug()
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
serial-8250_port-remove-dangerous-pr_debug.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Thu Oct 5 10:28:31 CEST 2017
From: Alexey Brodkin <Alexey.Brodkin@xxxxxxxxxxxx>
Date: Tue, 10 Jan 2017 18:11:29 +0300
Subject: serial: 8250_port: Remove dangerous pr_debug()
From: Alexey Brodkin <Alexey.Brodkin@xxxxxxxxxxxx>
[ 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 <abrodkin@xxxxxxxxxxxx>
Cc: Jiri Slaby <jslaby@xxxxxxxx>
Cc: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
Cc: Phillip Raffeck <phillip.raffeck@xxxxxx>
Cc: Anton Wuerfel <anton.wuerfel@xxxxxx>
Cc: "Matwey V. Kornilov" <matwey@xxxxxxxxxx>
Cc: Yegor Yefremov <yegorslists@xxxxxxxxxxxxxx>
Cc: Thor Thayer <tthayer@xxxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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);
Patches currently in stable-queue which might be from Alexey.Brodkin@xxxxxxxxxxxx are
queue-4.9/serial-8250_port-remove-dangerous-pr_debug.patch