Thomas Gleixner
fe2ba02c78
The current console/printk subsystem is protected by a Big Kernel Lock, (aka console_lock) which has ill defined semantics and is more or less stateless. This puts severe limitations on the console subsystem and makes forced takeover and output in emergency and panic situations a fragile endavour which is based on try and pray. The goal of non-BKL consoles is to break out of the console lock jail and to provide a new infrastructure that avoids the pitfalls and allows console drivers to be gradually converted over. The proposed infrastructure aims for the following properties: - Per console locking instead of global locking - Per console state which allows to make informed decisions - Stateful handover and takeover As a first step state is added to struct console. The per console state is an atomic_long_t with a 32bit bit field and on 64bit also a 32bit sequence for tracking the last printed ringbuffer sequence number. On 32bit the sequence is separate from state for obvious reasons which requires handling a few extra race conditions. Reserve state bits, which will be populated later in the series. Wire it up into the console register/unregister functionality and exclude such consoles from being handled in the console BKL mechanisms. Since the non-BKL consoles will not depend on the console lock/unlock dance for printing, only perform said dance if a BKL console is registered. The decision to use a bitfield was made as using a plain u32 with mask/shift operations turned out to result in uncomprehensible code. Co-developed-by: John Ogness <john.ogness@linutronix.de> Signed-off-by: John Ogness <john.ogness@linutronix.de> Signed-off-by: Thomas Gleixner (Intel) <tglx@linutronix.de> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.