• Petr Mladek's avatar
    Revert "printk: fix double printing with earlycon" · dac8bbba
    Petr Mladek authored
    This reverts commit cf39bf58.
    
    The commit regression to users that define both console=ttyS1
    and console=ttyS0 on the command line, see
    https://lkml.kernel.org/r/20170509082915.GA13236@bistromath.localdomain
    
    The kernel log messages always appeared only on one serial port. It is
    even documented in Documentation/admin-guide/serial-console.rst:
    
    "Note that you can only define one console per device type (serial,
    video)."
    
    The above mentioned commit changed the order in which the command line
    parameters are searched. As a result, the kernel log messages go to
    the last mentioned ttyS* instead of the first one.
    
    We long thought that using two console=ttyS* on the command line
    did not make sense. But then we realized that console= parameters
    were handled also by systemd, see
    http://0pointer.de/blog/projects/serial-console.html
    
    
    
    "By default systemd will instantiate one serial-getty@.service on
    the main kernel console, if it is not a virtual terminal."
    
    where
    
    "[4] If multiple kernel consoles are used simultaneously, the main
    console is the one listed first in /sys/class/tty/console/active,
    which is the last one listed on the kernel command line."
    
    This puts the original report into another light. The system is running
    in qemu. The first serial port is used to store the messages into a file.
    The second one is used to login to the system via a socket. It depends
    on systemd and the historic kernel behavior.
    
    By other words, systemd causes that it makes sense to define both
    console=ttyS1 console=ttyS0 on the command line. The kernel fix
    caused regression related to userspace (systemd) and need to be
    reverted.
    
    In addition, it went out that the fix helped only partially.
    The messages still were duplicated when the boot console was
    removed early by late_initcall(printk_late_init). Then the entire
    log was replayed when the same console was registered as a normal one.
    
    Link: 20170606160339.GC7604@pathway.suse.cz
    Cc: Aleksey Makarov <aleksey.makarov@linaro.org>
    Cc: Sabrina Dubroca <sd@queasysnail.net>
    Cc: Sudeep Holla <sudeep.holla@arm.com>
    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: Peter Hurley <peter@hurleysoftware.com>
    Cc: Jiri Slaby <jslaby@suse.com>
    Cc: Robin Murphy <robin.murphy@arm.com>,
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: "Nair, Jayachandran" <Jayachandran.Nair@cavium.com>
    Cc: linux-serial@vger.kernel.org
    Cc: linux-kernel@vger.kernel.org
    Reported-by: default avatarSabrina Dubroca <sd@queasysnail.net>
    Acked-by: default avatarSergey Senozhatsky <sergey.senozhatsky@gmail.com>
    Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
    dac8bbba
printk.c 78.6 KB