Messages in this thread Patch in this message | | | From | Alexey Brodkin <> | Subject | [PATCH] serial: 8250_port: Remove dangerous pr_debug() | Date | Tue, 10 Jan 2017 18:11:29 +0300 |
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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
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