From 757055ae8dedf5333af17b3b5b4b70ba9bc9da4e Mon Sep 17 00:00:00 2001 From: Petr Mladek Date: Wed, 11 Nov 2020 14:54:49 +0100 Subject: init/console: Use ttynull as a fallback when there is no console stdin, stdout, and stderr standard I/O stream are created for the init process. They are not available when there is no console registered for /dev/console. It might lead to a crash when the init process tries to use them, see the commit 48021f98130880dd742 ("printk: handle blank console arguments passed in."). Normally, ttySX and ttyX consoles are used as a fallback when no consoles are defined via the command line, device tree, or SPCR. But there will be no console registered when an invalid console name is configured or when the configured consoles do not exist on the system. Users even try to avoid the console intentionally, for example, by using console="" or console=null. It is used on production systems where the serial port or terminal are not visible to users. Pushing messages to these consoles would just unnecessary slowdown the system. Make sure that stdin, stdout, stderr, and /dev/console are always available by a fallback to the existing ttynull driver. It has been implemented for exactly this purpose but it was used only when explicitly configured. Reviewed-by: Greg Kroah-Hartman Reviewed-by: Guenter Roeck Tested-by: Guenter Roeck Acked-by: Sergey Senozhatsky Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20201111135450.11214-2-pmladek@suse.com --- drivers/tty/Kconfig | 14 -------------- drivers/tty/Makefile | 3 +-- drivers/tty/ttynull.c | 18 ++++++++++++++++++ 3 files changed, 19 insertions(+), 16 deletions(-) (limited to 'drivers/tty') diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig index 93fd984eb2f5..ca359bbd62f5 100644 --- a/drivers/tty/Kconfig +++ b/drivers/tty/Kconfig @@ -428,20 +428,6 @@ config MIPS_EJTAG_FDC_KGDB_CHAN help FDC channel number to use for KGDB. -config NULL_TTY - tristate "NULL TTY driver" - help - Say Y here if you want a NULL TTY which simply discards messages. - - This is useful to allow userspace applications which expect a console - device to work without modifications even when no console is - available or desired. - - In order to use this driver, you should redirect the console to this - TTY, or boot the kernel with console=ttynull. - - If unsure, say N. - config TRACE_ROUTER tristate "Trace data router for MIPI P1149.7 cJTAG standard" depends on TRACE_SINK diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile index 020b1cd9294f..f6b6bee0422d 100644 --- a/drivers/tty/Makefile +++ b/drivers/tty/Makefile @@ -2,7 +2,7 @@ obj-$(CONFIG_TTY) += tty_io.o n_tty.o tty_ioctl.o tty_ldisc.o \ tty_buffer.o tty_port.o tty_mutex.o \ tty_ldsem.o tty_baudrate.o tty_jobctrl.o \ - n_null.o + n_null.o ttynull.o obj-$(CONFIG_LEGACY_PTYS) += pty.o obj-$(CONFIG_UNIX98_PTYS) += pty.o obj-$(CONFIG_AUDIT) += tty_audit.o @@ -25,7 +25,6 @@ obj-$(CONFIG_ISI) += isicom.o obj-$(CONFIG_MOXA_INTELLIO) += moxa.o obj-$(CONFIG_MOXA_SMARTIO) += mxser.o obj-$(CONFIG_NOZOMI) += nozomi.o -obj-$(CONFIG_NULL_TTY) += ttynull.o obj-$(CONFIG_ROCKETPORT) += rocket.o obj-$(CONFIG_SYNCLINK_GT) += synclink_gt.o obj-$(CONFIG_SYNCLINKMP) += synclinkmp.o diff --git a/drivers/tty/ttynull.c b/drivers/tty/ttynull.c index 17f05b7eb6d3..eced70ec54e1 100644 --- a/drivers/tty/ttynull.c +++ b/drivers/tty/ttynull.c @@ -2,6 +2,13 @@ /* * Copyright (C) 2019 Axis Communications AB * + * The console is useful for userspace applications which expect a console + * device to work without modifications even when no console is available + * or desired. + * + * In order to use this driver, you should redirect the console to this + * TTY, or boot the kernel with console=ttynull. + * * Based on ttyprintk.c: * Copyright (C) 2010 Samo Pogacnik */ @@ -59,6 +66,17 @@ static struct console ttynull_console = { .device = ttynull_device, }; +void __init register_ttynull_console(void) +{ + if (!ttynull_driver) + return; + + if (add_preferred_console(ttynull_console.name, 0, NULL)) + return; + + register_console(&ttynull_console); +} + static int __init ttynull_init(void) { struct tty_driver *driver; -- cgit v1.2.3