Commit 848a9c10 authored by John Ogness's avatar John Ogness Committed by Petr Mladek
Browse files

printk: relieve console_lock of list synchronization duties 



The console_list_lock provides synchronization for console list and
console->flags updates. All call sites that were using the console_lock
for this synchronization have either switched to use the
console_list_lock or the SRCU list iterator.

Remove console_lock usage for console list updates and console->flags
updates.

Signed-off-by: default avatarJohn Ogness <john.ogness@linutronix.de>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20221116162152.193147-40-john.ogness@linutronix.de
parent e2b39652

kernel/printk/printk.c

+20 −24
Original line number Diff line number Diff line
@@ -86,8 +86,8 @@ EXPORT_SYMBOL(oops_in_progress); 
static DEFINE_MUTEX(console_mutex);



/*

 * console_sem protects console_list and console->flags updates, and also

 * provides serialization for access to the entire console driver system.

 * console_sem protects updates to console->seq and console_suspended,

 * and also provides serialization for console printing.

 */

static DEFINE_SEMAPHORE(console_sem);

HLIST_HEAD(console_list);
@@ -2640,10 +2640,10 @@ static int console_cpu_notify(unsigned int cpu) 
}



/**

 * console_lock - lock the console system for exclusive use.

 * console_lock - block the console subsystem from printing

 *

 * Acquires a lock which guarantees that the caller has

 * exclusive access to the console system and console_list.

 * Acquires a lock which guarantees that no consoles will

 * be in or enter their write() callback.

 *

 * Can sleep, returns nothing.

 */
@@ -2660,10 +2660,10 @@ void console_lock(void) 
EXPORT_SYMBOL(console_lock);



/**

 * console_trylock - try to lock the console system for exclusive use.

 * console_trylock - try to block the console subsystem from printing

 *

 * Try to acquire a lock which guarantees that the caller has exclusive

 * access to the console system and console_list.

 * Try to acquire a lock which guarantees that no consoles will

 * be in or enter their write() callback.

 *

 * returns 1 on success, and 0 on failure to acquire the lock.

 */
@@ -2920,10 +2920,10 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove 
}



/**

 * console_unlock - unlock the console system

 * console_unlock - unblock the console subsystem from printing

 *

 * Releases the console_lock which the caller holds on the console system

 * and the console driver list.

 * Releases the console_lock which the caller holds to block printing of

 * the console subsystem.

 *

 * While the console_lock was held, console output may have been buffered

 * by printk().  If this is the case, console_unlock(); emits
@@ -3110,9 +3110,7 @@ void console_stop(struct console *console) 
{

	__pr_flush(console, 1000, true);

	console_list_lock();

	console_lock();

	console_srcu_write_flags(console, console->flags & ~CON_ENABLED);

	console_unlock();

	console_list_unlock();



	/*
@@ -3128,9 +3126,7 @@ EXPORT_SYMBOL(console_stop); 
void console_start(struct console *console)

{

	console_list_lock();

	console_lock();

	console_srcu_write_flags(console, console->flags | CON_ENABLED);

	console_unlock();

	console_list_unlock();

	__pr_flush(console, 1000, true);

}
@@ -3247,6 +3243,12 @@ static void console_init_seq(struct console *newcon, bool bootcon_registered) 
		 * the furthest behind.

		 */

		if (bootcon_registered && !keep_bootcon) {

			/*

			 * Hold the console_lock to stop console printing and

			 * guarantee safe access to console->seq.

			 */

			console_lock();



			/*

			 * Flush all consoles and set the console to start at

			 * the next unprinted sequence number.
@@ -3273,6 +3275,8 @@ static void console_init_seq(struct console *newcon, bool bootcon_registered) 
					}

				}

			}



			console_unlock();

		}

	}

}
@@ -3371,7 +3375,6 @@ void register_console(struct console *newcon) 
	}



	newcon->dropped = 0;

	console_lock();

	console_init_seq(newcon, bootcon_registered);



	/*
@@ -3391,7 +3394,6 @@ void register_console(struct console *newcon) 
	} else {

		hlist_add_behind_rcu(&newcon->node, console_list.first);

	}

	console_unlock();



	/*

	 * No need to synchronize SRCU here! The caller does not rely
@@ -3439,15 +3441,11 @@ static int unregister_console_locked(struct console *console) 
	if (res > 0)

		return 0;



	console_lock();



	/* Disable it unconditionally */

	console_srcu_write_flags(console, console->flags & ~CON_ENABLED);



	if (!console_is_registered_locked(console)) {

		console_unlock();

	if (!console_is_registered_locked(console))

		return -ENODEV;

	}



	hlist_del_init_rcu(&console->node);
@@ -3463,8 +3461,6 @@ static int unregister_console_locked(struct console *console) 
	if (!hlist_empty(&console_list) && console->flags & CON_CONSDEV)

		console_srcu_write_flags(console_first(), console_first()->flags | CON_CONSDEV);



	console_unlock();



	/*

	 * Ensure that all SRCU list walks have completed. All contexts

	 * must not be able to see this console in the list so that any