Messages in this thread Patch in this message | | | From | Thomas Gleixner <> | Subject | [patch RFC 12/29] printk: Prepare for SCRU console list protection | Date | Sun, 11 Sep 2022 00:27:50 +0200 (CEST) |
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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> --- include/linux/console.h | 14 +++++++++++++- kernel/printk/printk.c | 16 +++++++++++++--- 2 files changed, 26 insertions(+), 4 deletions(-)
--- 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) { } @@ -172,6 +173,17 @@ extern void console_list_lock(void) __ac 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 * --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -90,6 +90,7 @@ 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 @@ -118,6 +119,10 @@ void lockdep_assert_console_list_lock_he 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 { @@ -3227,9 +3232,9 @@ void register_console(struct console *ne */ 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; @@ -3245,6 +3250,7 @@ void register_console(struct console *ne newcon->seq = prb_next_seq(prb); } console_unlock(); + /* No need to synchronize SRCU here! */ console_sysfs_notify(); /* @@ -3290,7 +3296,7 @@ static int console_unregister_locked(str if (hlist_unhashed(&console->node)) goto out_unlock; - hlist_del_init(&console->node); + hlist_del_init_rcu(&console->node); /* * <HISTORICAL> @@ -3305,6 +3311,10 @@ static int console_unregister_locked(str 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)
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