From: Alexey Brodkin <Alexey.Brodkin@synopsys.com>
To: linux-serial@vger.kernel.org
Cc: linux-kernel@vger.kernel.org,
Alexey Brodkin <Alexey.Brodkin@synopsys.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jiri Slaby <jslaby@suse.com>,
Peter Hurley <peter@hurleysoftware.com>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Phillip Raffeck <phillip.raffeck@fau.de>,
Anton Wuerfel <anton.wuerfel@fau.de>,
"Matwey V. Kornilov" <matwey@sai.msu.ru>,
Yegor Yefremov <yegorslists@googlemail.com>,
Thor Thayer <tthayer@opensource.altera.com>
Subject: [PATCH] serial: 8250_port: Remove dangerous pr_debug()
Date: Tue, 10 Jan 2017 18:11:29 +0300 [thread overview]
Message-ID: <1484061089-20070-1-git-send-email-abrodkin@synopsys.com> (raw)
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@synopsys.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Phillip Raffeck <phillip.raffeck@fau.de>
Cc: Anton Wuerfel <anton.wuerfel@fau.de>
Cc: "Matwey V. Kornilov" <matwey@sai.msu.ru>
Cc: Yegor Yefremov <yegorslists@googlemail.com>
Cc: Thor Thayer <tthayer@opensource.altera.com>
---
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
next reply other threads:[~2017-01-10 15:11 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-10 15:11 Alexey Brodkin [this message]
2017-01-10 15:56 ` [PATCH] serial: 8250_port: Remove dangerous pr_debug() Andy Shevchenko
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1484061089-20070-1-git-send-email-abrodkin@synopsys.com \
--to=alexey.brodkin@synopsys.com \
--cc=andriy.shevchenko@linux.intel.com \
--cc=anton.wuerfel@fau.de \
--cc=gregkh@linuxfoundation.org \
--cc=jslaby@suse.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-serial@vger.kernel.org \
--cc=matwey@sai.msu.ru \
--cc=peter@hurleysoftware.com \
--cc=phillip.raffeck@fau.de \
--cc=tthayer@opensource.altera.com \
--cc=yegorslists@googlemail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).