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-rw-r--r--debian/patches-rt/0075-printk-Add-non-BKL-nbcon-console-basic-infrastructur.patch261
1 files changed, 261 insertions, 0 deletions
diff --git a/debian/patches-rt/0075-printk-Add-non-BKL-nbcon-console-basic-infrastructur.patch b/debian/patches-rt/0075-printk-Add-non-BKL-nbcon-console-basic-infrastructur.patch
new file mode 100644
index 0000000000..00f7850c36
--- /dev/null
+++ b/debian/patches-rt/0075-printk-Add-non-BKL-nbcon-console-basic-infrastructur.patch
@@ -0,0 +1,261 @@
+From: Thomas Gleixner <tglx@linutronix.de>
+Date: Sat, 16 Sep 2023 21:26:00 +0206
+Subject: [PATCH 075/134] printk: Add non-BKL (nbcon) console basic
+ infrastructure
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz
+
+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 endeavour that is based on try and pray.
+
+The goal of non-BKL (nbcon) consoles is to break out of the console lock
+jail and to provide a new infrastructure that avoids the pitfalls and
+also 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 that 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_t using a 32bit bit field.
+
+Reserve state bits, which will be populated later in the series. Wire
+it up into the console register/unregister functionality.
+
+It was decided to use a bitfield because using a plain u32 with
+mask/shift operations resulted 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>
+Reviewed-by: Petr Mladek <pmladek@suse.com>
+Signed-off-by: Petr Mladek <pmladek@suse.com>
+Link: https://lore.kernel.org/r/20230916192007.608398-2-john.ogness@linutronix.de
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+---
+ include/linux/console.h | 31 ++++++++++++++++++++
+ kernel/printk/Makefile | 2 -
+ kernel/printk/internal.h | 8 +++++
+ kernel/printk/nbcon.c | 70 +++++++++++++++++++++++++++++++++++++++++++++++
+ kernel/printk/printk.c | 13 ++++++--
+ 5 files changed, 120 insertions(+), 4 deletions(-)
+ create mode 100644 kernel/printk/nbcon.c
+
+--- a/include/linux/console.h
++++ b/include/linux/console.h
+@@ -156,6 +156,8 @@ static inline int con_debug_leave(void)
+ * /dev/kmesg which requires a larger output buffer.
+ * @CON_SUSPENDED: Indicates if a console is suspended. If true, the
+ * printing callbacks must not be called.
++ * @CON_NBCON: Console can operate outside of the legacy style console_lock
++ * constraints.
+ */
+ enum cons_flags {
+ CON_PRINTBUFFER = BIT(0),
+@@ -166,9 +168,33 @@ enum cons_flags {
+ CON_BRL = BIT(5),
+ CON_EXTENDED = BIT(6),
+ CON_SUSPENDED = BIT(7),
++ CON_NBCON = BIT(8),
+ };
+
+ /**
++ * struct nbcon_state - console state for nbcon consoles
++ * @atom: Compound of the state fields for atomic operations
++ *
++ * To be used for reading and preparing of the value stored in the nbcon
++ * state variable @console::nbcon_state.
++ */
++struct nbcon_state {
++ union {
++ unsigned int atom;
++ struct {
++ };
++ };
++};
++
++/*
++ * The nbcon_state struct is used to easily create and interpret values that
++ * are stored in the @console::nbcon_state variable. Ensure this struct stays
++ * within the size boundaries of the atomic variable's underlying type in
++ * order to avoid any accidental truncation.
++ */
++static_assert(sizeof(struct nbcon_state) <= sizeof(int));
++
++/**
+ * struct console - The console descriptor structure
+ * @name: The name of the console driver
+ * @write: Write callback to output messages (Optional)
+@@ -187,6 +213,8 @@ enum cons_flags {
+ * @dropped: Number of unreported dropped ringbuffer records
+ * @data: Driver private data
+ * @node: hlist node for the console list
++ *
++ * @nbcon_state: State for nbcon consoles
+ */
+ struct console {
+ char name[16];
+@@ -206,6 +234,9 @@ struct console {
+ unsigned long dropped;
+ void *data;
+ struct hlist_node node;
++
++ /* nbcon console specific members */
++ atomic_t __private nbcon_state;
+ };
+
+ #ifdef CONFIG_LOCKDEP
+--- a/kernel/printk/Makefile
++++ b/kernel/printk/Makefile
+@@ -1,6 +1,6 @@
+ # SPDX-License-Identifier: GPL-2.0-only
+ obj-y = printk.o
+-obj-$(CONFIG_PRINTK) += printk_safe.o
++obj-$(CONFIG_PRINTK) += printk_safe.o nbcon.o
+ obj-$(CONFIG_A11Y_BRAILLE_CONSOLE) += braille.o
+ obj-$(CONFIG_PRINTK_INDEX) += index.o
+
+--- a/kernel/printk/internal.h
++++ b/kernel/printk/internal.h
+@@ -3,6 +3,7 @@
+ * internal.h - printk internal definitions
+ */
+ #include <linux/percpu.h>
++#include <linux/console.h>
+
+ #if defined(CONFIG_PRINTK) && defined(CONFIG_SYSCTL)
+ void __init printk_sysctl_init(void);
+@@ -61,6 +62,10 @@ void defer_console_output(void);
+
+ u16 printk_parse_prefix(const char *text, int *level,
+ enum printk_info_flags *flags);
++
++void nbcon_init(struct console *con);
++void nbcon_cleanup(struct console *con);
++
+ #else
+
+ #define PRINTK_PREFIX_MAX 0
+@@ -76,6 +81,9 @@ u16 printk_parse_prefix(const char *text
+ #define printk_safe_exit_irqrestore(flags) local_irq_restore(flags)
+
+ static inline bool printk_percpu_data_ready(void) { return false; }
++static inline void nbcon_init(struct console *con) { }
++static inline void nbcon_cleanup(struct console *con) { }
++
+ #endif /* CONFIG_PRINTK */
+
+ /**
+--- /dev/null
++++ b/kernel/printk/nbcon.c
+@@ -0,0 +1,70 @@
++// SPDX-License-Identifier: GPL-2.0-only
++// Copyright (C) 2022 Linutronix GmbH, John Ogness
++// Copyright (C) 2022 Intel, Thomas Gleixner
++
++#include <linux/kernel.h>
++#include <linux/console.h>
++#include "internal.h"
++/*
++ * Printk console printing implementation for consoles which does not depend
++ * on the legacy style console_lock mechanism.
++ */
++
++/**
++ * nbcon_state_set - Helper function to set the console state
++ * @con: Console to update
++ * @new: The new state to write
++ *
++ * Only to be used when the console is not yet or no longer visible in the
++ * system. Otherwise use nbcon_state_try_cmpxchg().
++ */
++static inline void nbcon_state_set(struct console *con, struct nbcon_state *new)
++{
++ atomic_set(&ACCESS_PRIVATE(con, nbcon_state), new->atom);
++}
++
++/**
++ * nbcon_state_read - Helper function to read the console state
++ * @con: Console to read
++ * @state: The state to store the result
++ */
++static inline void nbcon_state_read(struct console *con, struct nbcon_state *state)
++{
++ state->atom = atomic_read(&ACCESS_PRIVATE(con, nbcon_state));
++}
++
++/**
++ * nbcon_state_try_cmpxchg() - Helper function for atomic_try_cmpxchg() on console state
++ * @con: Console to update
++ * @cur: Old/expected state
++ * @new: New state
++ *
++ * Return: True on success. False on fail and @cur is updated.
++ */
++static inline bool nbcon_state_try_cmpxchg(struct console *con, struct nbcon_state *cur,
++ struct nbcon_state *new)
++{
++ return atomic_try_cmpxchg(&ACCESS_PRIVATE(con, nbcon_state), &cur->atom, new->atom);
++}
++
++/**
++ * nbcon_init - Initialize the nbcon console specific data
++ * @con: Console to initialize
++ */
++void nbcon_init(struct console *con)
++{
++ struct nbcon_state state = { };
++
++ nbcon_state_set(con, &state);
++}
++
++/**
++ * nbcon_cleanup - Cleanup the nbcon console specific data
++ * @con: Console to cleanup
++ */
++void nbcon_cleanup(struct console *con)
++{
++ struct nbcon_state state = { };
++
++ nbcon_state_set(con, &state);
++}
+--- a/kernel/printk/printk.c
++++ b/kernel/printk/printk.c
+@@ -3326,9 +3326,10 @@ static void try_enable_default_console(s
+ newcon->flags |= CON_CONSDEV;
+ }
+
+-#define con_printk(lvl, con, fmt, ...) \
+- printk(lvl pr_fmt("%sconsole [%s%d] " fmt), \
+- (con->flags & CON_BOOT) ? "boot" : "", \
++#define con_printk(lvl, con, fmt, ...) \
++ printk(lvl pr_fmt("%s%sconsole [%s%d] " fmt), \
++ (con->flags & CON_NBCON) ? "" : "legacy ", \
++ (con->flags & CON_BOOT) ? "boot" : "", \
+ con->name, con->index, ##__VA_ARGS__)
+
+ static void console_init_seq(struct console *newcon, bool bootcon_registered)
+@@ -3488,6 +3489,9 @@ void register_console(struct console *ne
+ newcon->dropped = 0;
+ console_init_seq(newcon, bootcon_registered);
+
++ if (newcon->flags & CON_NBCON)
++ nbcon_init(newcon);
++
+ /*
+ * Put this console in the list - keep the
+ * preferred driver at the head of the list.
+@@ -3579,6 +3583,9 @@ static int unregister_console_locked(str
+ */
+ synchronize_srcu(&console_srcu);
+
++ if (console->flags & CON_NBCON)
++ nbcon_cleanup(console);
++
+ console_sysfs_notify();
+
+ if (console->exit)