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Code Issues Releases Wiki Activity

printk: relieve console_lock of list synchronization duties

Browse source 
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: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20221116162152.193147-40-john.ogness@linutronix.de
This commit is contained in:
John Ogness 2022-11-16 17:27:51 +01:06 committed by Petr Mladek
parent e2b3965228
commit 848a9c1066
1 changed files with 20 additions and 24 deletions
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44
kernel/printk/printk.c
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@ -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