From 68af43173d3fcece70bef49cb992c64c4c68ff23 Mon Sep 17 00:00:00 2001 From: Dmitry Safonov Date: Mon, 2 Mar 2020 17:51:35 +0000 Subject: serial/sysrq: Add MAGIC_SYSRQ_SERIAL_SEQUENCE Many embedded boards have a disconnected TTL level serial which can generate some garbage that can lead to spurious false sysrq detects. Currently, sysrq can be either completely disabled for serial console or always disabled (with CONFIG_MAGIC_SYSRQ_SERIAL), since commit 732dbf3a6104 ("serial: do not accept sysrq characters via serial port") At Arista, we have such boards that can generate BREAK and random garbage. While disabling sysrq for serial console would solve the problem with spurious false sysrq triggers, it's also desirable to have a way to enable sysrq back. As a measure of balance between on and off options, add MAGIC_SYSRQ_SERIAL_SEQUENCE which is a string sequence that can enable sysrq if it follows BREAK on a serial line. The longer the string - the less likely it may be in the garbage. Having the way to enable sysrq was beneficial to debug lockups with a manual investigation in field and on the other side preventing false sysrq detections. Based-on-patch-by: Vasiliy Khoruzhick Signed-off-by: Dmitry Safonov Link: https://lore.kernel.org/r/20200302175135.269397-3-dima@arista.com Signed-off-by: Greg Kroah-Hartman --- lib/Kconfig.debug | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'lib') diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 69def4a9df00..38a8f3c99579 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -431,6 +431,14 @@ config MAGIC_SYSRQ_SERIAL This option allows you to decide whether you want to enable the magic SysRq key. +config MAGIC_SYSRQ_SERIAL_SEQUENCE + string "Char sequence that enables magic SysRq over serial" + depends on MAGIC_SYSRQ_SERIAL + default "" + help + Specifies a sequence of characters that can follow BREAK to enable + SysRq on a serial console. + config DEBUG_FS bool "Debug Filesystem" help -- cgit v1.2.3 From d3394b3d51828d99d46bf38a1004517c0ff971a8 Mon Sep 17 00:00:00 2001 From: Dmitry Safonov Date: Fri, 6 Mar 2020 15:31:56 +0000 Subject: serial/sysrq: Add a help-string for MAGIC_SYSRQ_SERIAL_SEQUENCE To make it more obvious what almost everyone wants to set here. Cc: Iurii Zaikin Cc: Jiri Slaby Cc: Joe Perches Cc: Randy Dunlap Cc: Vasiliy Khoruzhick Cc: linux-serial@vger.kernel.org Suggested-by: Greg Kroah-Hartman Signed-off-by: Dmitry Safonov Link: https://lore.kernel.org/r/20200306153156.579921-1-dima@arista.com Signed-off-by: Greg Kroah-Hartman --- lib/Kconfig.debug | 2 ++ 1 file changed, 2 insertions(+) (limited to 'lib') diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 38a8f3c99579..c4a45817918a 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -439,6 +439,8 @@ config MAGIC_SYSRQ_SERIAL_SEQUENCE Specifies a sequence of characters that can follow BREAK to enable SysRq on a serial console. + If unsure, leave an empty string and the option will not be enabled. + config DEBUG_FS bool "Debug Filesystem" help -- cgit v1.2.3