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Message-ID: <20170914155051.8289-35-alexander.levin@verizon.com> Date: Thu, 14 Sep 2017 15:51:15 +0000 From: "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com> To: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "stable@...r.kernel.org" <stable@...r.kernel.org> Cc: Alexey Brodkin <Alexey.Brodkin@...opsys.com>, Alexey Brodkin <abrodkin@...opsys.com>, Jiri Slaby <jslaby@...e.com>, Peter Hurley <peter@...leysoftware.com>, Phillip Raffeck <phillip.raffeck@....de>, "Anton Wuerfel" <anton.wuerfel@....de>, "Matwey V. Kornilov" <matwey@....msu.ru>, Yegor Yefremov <yegorslists@...glemail.com>, Thor Thayer <tthayer@...nsource.altera.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com> Subject: [PATCH for 4.9 35/59] serial: 8250_port: Remove dangerous pr_debug() From: Alexey Brodkin <Alexey.Brodkin@...opsys.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 <abrodkin@...opsys.com> Cc: Jiri Slaby <jslaby@...e.com> Cc: Peter Hurley <peter@...leysoftware.com> Cc: Phillip Raffeck <phillip.raffeck@....de> Cc: Anton Wuerfel <anton.wuerfel@....de> Cc: "Matwey V. Kornilov" <matwey@....msu.ru> Cc: Yegor Yefremov <yegorslists@...glemail.com> Cc: Thor Thayer <tthayer@...nsource.altera.com> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> Signed-off-by: Sasha Levin <alexander.levin@...izon.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 f24d3030b98c..1ef31e3ee4a1 100644 --- 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_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 @@ -1817,8 +1815,6 @@ 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); -- 2.11.0
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