printk: Prepare for SRCU console list protection

Provide an NMI-safe SRCU protected variant to walk the console list.

Note that all console fields are now set before adding the console
to the list to avoid the console becoming visible by SCRU readers
before being fully initialized.

This is a preparatory change for a new console infrastructure which
operates independent of the console BKL.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20221116162152.193147-4-john.ogness@linutronix.de
This commit is contained in:
John Ogness 2022-11-16 17:27:15 +01:06 committed by Petr Mladek
parent d9a4af5690
commit 6c4afa7914
3 changed files with 105 additions and 21 deletions

View File

@ -222,6 +222,7 @@ ForEachMacros:
- 'for_each_component_dais'
- 'for_each_component_dais_safe'
- 'for_each_console'
- 'for_each_console_srcu'
- 'for_each_cpu'
- 'for_each_cpu_and'
- 'for_each_cpu_not'

View File

@ -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;
@ -158,8 +158,34 @@ struct console {
struct hlist_node node;
};
#ifdef CONFIG_DEBUG_LOCK_ALLOC
extern bool console_srcu_read_lock_is_held(void);
#else
static inline bool console_srcu_read_lock_is_held(void)
{
return 1;
}
#endif
extern int console_srcu_read_lock(void);
extern void console_srcu_read_unlock(int cookie);
extern struct hlist_head console_list;
/**
* for_each_console_srcu() - Iterator over registered consoles
* @con: struct console pointer used as loop cursor
*
* Although SRCU guarantees the console list will be consistent, the
* struct console fields may be updated by other CPUs while iterating.
*
* 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_console() allows you to iterate on each console
*/

View File

@ -85,6 +85,7 @@ EXPORT_SYMBOL(oops_in_progress);
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
@ -104,6 +105,13 @@ static struct lockdep_map console_lock_dep_map = {
};
#endif
#ifdef CONFIG_DEBUG_LOCK_ALLOC
bool console_srcu_read_lock_is_held(void)
{
return srcu_read_lock_held(&console_srcu);
}
#endif
enum devkmsg_log_bits {
__DEVKMSG_LOG_BIT_ON = 0,
__DEVKMSG_LOG_BIT_OFF,
@ -219,6 +227,32 @@ int devkmsg_sysctl_set_loglvl(struct ctl_table *table, int write,
}
#endif /* CONFIG_PRINTK && CONFIG_SYSCTL */
/**
* console_srcu_read_lock - Register a new reader for the
* SRCU-protected console list
*
* Use for_each_console_srcu() to iterate the console list
*
* Context: Any context.
*/
int console_srcu_read_lock(void)
{
return srcu_read_lock_nmisafe(&console_srcu);
}
EXPORT_SYMBOL(console_srcu_read_lock);
/**
* console_srcu_read_unlock - Unregister an old reader from
* the SRCU-protected console list
*
* Counterpart to console_srcu_read_lock()
*/
void console_srcu_read_unlock(int cookie)
{
srcu_read_unlock_nmisafe(&console_srcu, cookie);
}
EXPORT_SYMBOL(console_srcu_read_unlock);
/*
* Helper macros to handle lockdep when locking/unlocking console_sem. We use
* macros instead of functions so that _RET_IP_ contains useful information.
@ -2989,6 +3023,14 @@ void console_stop(struct console *console)
console_lock();
console->flags &= ~CON_ENABLED;
console_unlock();
/*
* Ensure that all SRCU list walks have completed. All contexts must
* be able to see that this console is disabled so that (for example)
* the caller can suspend the port without risk of another context
* using the port.
*/
synchronize_srcu(&console_srcu);
}
EXPORT_SYMBOL(console_stop);
@ -3179,25 +3221,6 @@ void register_console(struct console *newcon)
newcon->flags &= ~CON_PRINTBUFFER;
}
/*
* Put this console in the list - keep the
* preferred driver at the head of the list.
*/
console_lock();
if (hlist_empty(&console_list)) {
/* Ensure CON_CONSDEV is always set for the head. */
newcon->flags |= CON_CONSDEV;
hlist_add_head(&newcon->node, &console_list);
} else if (newcon->flags & CON_CONSDEV) {
/* Only the new head can have CON_CONSDEV set. */
console_first()->flags &= ~CON_CONSDEV;
hlist_add_head(&newcon->node, &console_list);
} else {
hlist_add_behind(&newcon->node, console_list.first);
}
newcon->dropped = 0;
if (newcon->flags & CON_PRINTBUFFER) {
/* Get a consistent copy of @syslog_seq. */
@ -3208,7 +3231,33 @@ void register_console(struct console *newcon)
/* Begin with next message. */
newcon->seq = prb_next_seq(prb);
}
/*
* Put this console in the list - keep the
* preferred driver at the head of the list.
*/
console_lock();
if (hlist_empty(&console_list)) {
/* Ensure CON_CONSDEV is always set for the head. */
newcon->flags |= CON_CONSDEV;
hlist_add_head_rcu(&newcon->node, &console_list);
} else if (newcon->flags & CON_CONSDEV) {
/* Only the new head can have CON_CONSDEV set. */
console_first()->flags &= ~CON_CONSDEV;
hlist_add_head_rcu(&newcon->node, &console_list);
} else {
hlist_add_behind_rcu(&newcon->node, console_list.first);
}
console_unlock();
/*
* No need to synchronize SRCU here! The caller does not rely
* on all contexts being able to see the new console before
* register_console() completes.
*/
console_sysfs_notify();
/*
@ -3254,7 +3303,7 @@ int unregister_console(struct console *console)
return -ENODEV;
}
hlist_del_init(&console->node);
hlist_del_init_rcu(&console->node);
/*
* <HISTORICAL>
@ -3269,6 +3318,14 @@ int unregister_console(struct console *console)
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
* exit/cleanup routines can be performed safely.
*/
synchronize_srcu(&console_srcu);
console_sysfs_notify();
if (console->exit)