From: Thomas Gleixner <tglx@linutronix.de>
Provide a SRCU protected variant to walk the console list.
Preperatory change for a new console infrastructure which operates
independent of console BKL.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
include/linux/console.h | 14 +++++++++++++-
kernel/printk/printk.c | 16 +++++++++++++---
2 files changed, 26 insertions(+), 4 deletions(-)
diff --git a/include/linux/console.h b/include/linux/console.h
index 1e3d0a50cef1..dc0df9d9e7d9 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -15,7 +15,7 @@
#define _LINUX_CONSOLE_H_ 1
#include <linux/atomic.h>
-#include <linux/list.h>
+#include <linux/rculist.h>
#include <linux/types.h>
struct vc_data;
@@ -161,6 +161,7 @@ struct console {
#ifdef CONFIG_LOCKDEP
extern void lockdep_assert_console_lock_held(void);
extern void lockdep_assert_console_list_lock_held(void);
+extern bool console_srcu_read_lock_is_held(void);
#else
static inline void lockdep_assert_console_lock_held(void) { }
static inline void lockdep_assert_console_list_lock_held(void) { }
@@ -171,6 +172,17 @@ extern struct hlist_head console_list;
extern void console_list_lock(void) __acquires(console_mutex);
extern void console_list_unlock(void) __releases(console_mutex);
+/**
+ * for_each_console_srcu() - Iterator over registered consoles
+ * @con: struct console pointer used as loop cursor
+ *
+ * Requires console_srcu_read_lock to be held. Can be invoked from
+ * any context.
+ */
+#define for_each_console_srcu(con) \
+ hlist_for_each_entry_srcu(con, &console_list, node, \
+ console_srcu_read_lock_is_held())
+
/**
* for_each_registered_console() - Iterator over registered consoles
* @con: struct console pointer used as loop cursor
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index f1d31dcbd6ba..7e6d1cd34452 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -93,6 +93,7 @@ static DEFINE_MUTEX(console_mutex);
static DEFINE_SEMAPHORE(console_sem);
HLIST_HEAD(console_list);
EXPORT_SYMBOL_GPL(console_list);
+DEFINE_STATIC_SRCU(console_srcu);
/*
* System may need to suppress printk message under certain
@@ -121,6 +122,10 @@ void lockdep_assert_console_list_lock_held(void)
lockdep_assert_held(&console_mutex);
}
+bool console_srcu_read_lock_is_held(void)
+{
+ return srcu_read_lock_held(&console_srcu);
+}
#endif
enum devkmsg_log_bits {
@@ -3232,9 +3237,9 @@ void register_console(struct console *newcon)
*/
console_lock();
if (newcon->flags & CON_CONSDEV || hlist_empty(&console_list))
- hlist_add_head(&newcon->node, &console_list);
+ hlist_add_head_rcu(&newcon->node, &console_list);
else
- hlist_add_behind(&newcon->node, console_list.first);
+ hlist_add_behind_rcu(&newcon->node, console_list.first);
/* Ensure this flag is always set for the head of the list */
cons_first()->flags |= CON_CONSDEV;
@@ -3250,6 +3255,7 @@ void register_console(struct console *newcon)
newcon->seq = prb_next_seq(prb);
}
console_unlock();
+ /* No need to synchronize SRCU here! */
console_sysfs_notify();
/*
@@ -3295,7 +3301,7 @@ static int console_unregister_locked(struct console *console)
if (hlist_unhashed(&console->node))
goto out_unlock;
- hlist_del_init(&console->node);
+ hlist_del_init_rcu(&console->node);
/*
* <HISTORICAL>
@@ -3310,6 +3316,10 @@ static int console_unregister_locked(struct console *console)
cons_first()->flags |= CON_CONSDEV;
console_unlock();
+
+ /* Ensure that all SRCU list walks have completed */
+ synchronize_srcu(&console_srcu);
+
console_sysfs_notify();
if (console->exit)
--
2.30.2