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printk: Convert console_drivers list to hlist

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Replace the open coded single linked list with a hlist so a conversion
to SRCU protected list walks can reuse the existing primitives.

Co-developed-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20221116162152.193147-3-john.ogness@linutronix.de
This commit is contained in:
Thomas Gleixner 2022-11-16 17:27:14 +01:06 committed by Petr Mladek
parent 9e409c4778
commit d9a4af5690
3 changed files with 62 additions and 50 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
fs/proc/consoles.c
View File

@ -74,8 +74,9 @@ static void *c_start(struct seq_file *m, loff_t *pos)
static void *c_next(struct seq_file *m, void *v, loff_t *pos)
{
struct console *con = v;
++*pos;
return con->next;
return hlist_entry_safe(con->node.next, struct console, node);
}
static void c_stop(struct seq_file *m, void *v)

8
include/linux/console.h
View File

@ -15,6 +15,7 @@
#define _LINUX_CONSOLE_H_ 1
#include <linux/atomic.h>
#include <linux/list.h>
#include <linux/types.h>
struct vc_data;
@ -154,14 +155,16 @@ struct console {
u64 seq;
unsigned long dropped;
void *data;
struct console *next;
struct hlist_node node;
};
extern struct hlist_head console_list;
/*
* for_each_console() allows you to iterate on each console
*/
#define for_each_console(con) \
for (con = console_drivers; con != NULL; con = con->next)
hlist_for_each_entry(con, &console_list, node)
extern int console_set_on_cmdline;
extern struct console *early_console;
@ -174,7 +177,6 @@ enum con_flush_mode {
extern int add_preferred_console(char *name, int idx, char *options);
extern void register_console(struct console *);
extern int unregister_console(struct console *);
extern struct console *console_drivers;
extern void console_lock(void);
extern int console_trylock(void);
extern void console_unlock(void);

101
kernel/printk/printk.c
View File

@ -79,13 +79,12 @@ int oops_in_progress;
EXPORT_SYMBOL(oops_in_progress);
/*
* console_sem protects the console_drivers list, and also
* provides serialisation for access to the entire console
* driver system.
* console_sem protects console_list and console->flags updates, and also
* provides serialization for access to the entire console driver system.
*/
static DEFINE_SEMAPHORE(console_sem);
struct console *console_drivers;
EXPORT_SYMBOL_GPL(console_drivers);
HLIST_HEAD(console_list);
EXPORT_SYMBOL_GPL(console_list);
/*
* System may need to suppress printk message under certain
@ -2556,7 +2555,7 @@ static int console_cpu_notify(unsigned int cpu)
* console_lock - lock the console system for exclusive use.
*
* Acquires a lock which guarantees that the caller has
* exclusive access to the console system and the console_drivers list.
* exclusive access to the console system and console_list.
*
* Can sleep, returns nothing.
*/
@ -2576,7 +2575,7 @@ EXPORT_SYMBOL(console_lock);
* console_trylock - try to lock the console system for exclusive use.
*
* Try to acquire a lock which guarantees that the caller has exclusive
* access to the console system and the console_drivers list.
* access to the console system and console_list.
*
* returns 1 on success, and 0 on failure to acquire the lock.
*/
@ -2940,11 +2939,20 @@ void console_flush_on_panic(enum con_flush_mode mode)
console_may_schedule = 0;
if (mode == CONSOLE_REPLAY_ALL) {
struct hlist_node *tmp;
struct console *c;
u64 seq;
seq = prb_first_valid_seq(prb);
for_each_console(c)
/*
* This cannot use for_each_console() because it's not established
* that the current context has console locked and neither there is
* a guarantee that there is no concurrency in that case.
*
* Open code it for documentation purposes and pretend that
* it works.
*/
hlist_for_each_entry_safe(c, tmp, &console_list, node)
c->seq = seq;
}
console_unlock();
@ -3081,6 +3089,9 @@ static void try_enable_default_console(struct console *newcon)
(con->flags & CON_BOOT) ? "boot" : "", \
con->name, con->index, ##__VA_ARGS__)
#define console_first() \
hlist_entry(console_list.first, struct console, node)
/*
* The console driver calls this routine during kernel initialization
* to register the console printing procedure with printk() and to
@ -3140,8 +3151,8 @@ void register_console(struct console *newcon)
* flag set and will be first in the list.
*/
if (preferred_console < 0) {
if (!console_drivers || !console_drivers->device ||
console_drivers->flags & CON_BOOT) {
if (hlist_empty(&console_list) || !console_first()->device ||
console_first()->flags & CON_BOOT) {
try_enable_default_console(newcon);
}
}
@ -3169,20 +3180,22 @@ void register_console(struct console *newcon)
}
/*
* Put this console in the list - keep the
* preferred driver at the head of the list.
* Put this console in the list - keep the
* preferred driver at the head of the list.
*/
console_lock();
if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
newcon->next = console_drivers;
console_drivers = newcon;
if (newcon->next)
newcon->next->flags &= ~CON_CONSDEV;
/* Ensure this flag is always set for the head of the list */
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 {
newcon->next = console_drivers->next;
console_drivers->next = newcon;
hlist_add_behind(&newcon->node, console_list.first);
}
newcon->dropped = 0;
@ -3209,16 +3222,18 @@ void register_console(struct console *newcon)
if (bootcon_enabled &&
((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV) &&
!keep_bootcon) {
for_each_console(con)
struct hlist_node *tmp;
hlist_for_each_entry_safe(con, tmp, &console_list, node) {
if (con->flags & CON_BOOT)
unregister_console(con);
}
}
}
EXPORT_SYMBOL(register_console);
int unregister_console(struct console *console)
{
struct console *con;
int res;
con_printk(KERN_INFO, console, "disabled\n");
@ -3229,32 +3244,30 @@ int unregister_console(struct console *console)
if (res > 0)
return 0;
res = -ENODEV;
console_lock();
if (console_drivers == console) {
console_drivers=console->next;
res = 0;
} else {
for_each_console(con) {
if (con->next == console) {
con->next = console->next;
res = 0;
break;
}
}
/* Disable it unconditionally */
console->flags &= ~CON_ENABLED;
if (hlist_unhashed(&console->node)) {
console_unlock();
return -ENODEV;
}
if (res)
goto out_disable_unlock;
hlist_del_init(&console->node);
/*
* <HISTORICAL>
* If this isn't the last console and it has CON_CONSDEV set, we
* need to set it on the next preferred console.
* </HISTORICAL>
*
* The above makes no sense as there is no guarantee that the next
* console has any device attached. Oh well....
*/
if (console_drivers != NULL && console->flags & CON_CONSDEV)
console_drivers->flags |= CON_CONSDEV;
if (!hlist_empty(&console_list) && console->flags & CON_CONSDEV)
console_first()->flags |= CON_CONSDEV;
console->flags &= ~CON_ENABLED;
console_unlock();
console_sysfs_notify();
@ -3262,12 +3275,6 @@ int unregister_console(struct console *console)
res = console->exit(console);
return res;
out_disable_unlock:
console->flags &= ~CON_ENABLED;
console_unlock();
return res;
}
EXPORT_SYMBOL(unregister_console);
@ -3317,10 +3324,11 @@ void __init console_init(void)
*/
static int __init printk_late_init(void)
{
struct hlist_node *tmp;
struct console *con;
int ret;
for_each_console(con) {
hlist_for_each_entry_safe(con, tmp, &console_list, node) {
if (!(con->flags & CON_BOOT))
continue;
@ -3340,6 +3348,7 @@ static int __init printk_late_init(void)
unregister_console(con);
}
}
ret = cpuhp_setup_state_nocalls(CPUHP_PRINTK_DEAD, "printk:dead", NULL,
console_cpu_notify);
WARN_ON(ret < 0);