4.9-stable review patch. If anyone has any objections, please let me know.
------------------ From: Alexey Brodkin <[email protected]> [ 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 <[email protected]> Cc: Jiri Slaby <[email protected]> Cc: Peter Hurley <[email protected]> Cc: Phillip Raffeck <[email protected]> Cc: Anton Wuerfel <[email protected]> Cc: "Matwey V. Kornilov" <[email protected]> Cc: Yegor Yefremov <[email protected]> Cc: Thor Thayer <[email protected]> Reviewed-by: Andy Shevchenko <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> Signed-off-by: Sasha Levin <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- 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);
