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authorPetr Mladek <pmladek@suse.com>2022-12-08 11:46:56 +0100
committerPetr Mladek <pmladek@suse.com>2022-12-08 11:46:56 +0100
commit6b2b0d839acaa84f05a77184370f793752e786e9 (patch)
treed051c2ca80acc8a442277410d23a2053685f8a85 /kernel/printk/printk.c
parent7365df19e8ff7a031e1557616fc0b3aa6d794d7e (diff)
parent5074ffbec67ac592614901771d3a15e1198d759d (diff)
Merge branch 'rework/console-list-lock' into for-linus
Diffstat (limited to 'kernel/printk/printk.c')
-rw-r--r--kernel/printk/printk.c496
1 files changed, 384 insertions, 112 deletions
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index eec87ddcaa45..7decf1e9c486 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -79,13 +79,20 @@ 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_mutex protects console_list updates and console->flags updates.
+ * The flags are synchronized only for consoles that are registered, i.e.
+ * accessible via the console list.
+ */
+static DEFINE_MUTEX(console_mutex);
+
+/*
+ * console_sem protects updates to console->seq and console_suspended,
+ * and also provides serialization for console printing.
*/
static DEFINE_SEMAPHORE(console_sem);
-struct console *console_drivers;
-EXPORT_SYMBOL_GPL(console_drivers);
+HLIST_HEAD(console_list);
+EXPORT_SYMBOL_GPL(console_list);
+DEFINE_STATIC_SRCU(console_srcu);
/*
* System may need to suppress printk message under certain
@@ -103,6 +110,19 @@ static int __read_mostly suppress_panic_printk;
static struct lockdep_map console_lock_dep_map = {
.name = "console_lock"
};
+
+void lockdep_assert_console_list_lock_held(void)
+{
+ lockdep_assert_held(&console_mutex);
+}
+EXPORT_SYMBOL(lockdep_assert_console_list_lock_held);
+#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 {
@@ -220,6 +240,69 @@ int devkmsg_sysctl_set_loglvl(struct ctl_table *table, int write,
}
#endif /* CONFIG_PRINTK && CONFIG_SYSCTL */
+/**
+ * console_list_lock - Lock the console list
+ *
+ * For console list or console->flags updates
+ */
+void console_list_lock(void)
+{
+ /*
+ * In unregister_console() and console_force_preferred_locked(),
+ * synchronize_srcu() is called with the console_list_lock held.
+ * Therefore it is not allowed that the console_list_lock is taken
+ * with the srcu_lock held.
+ *
+ * Detecting if this context is really in the read-side critical
+ * section is only possible if the appropriate debug options are
+ * enabled.
+ */
+ WARN_ON_ONCE(debug_lockdep_rcu_enabled() &&
+ srcu_read_lock_held(&console_srcu));
+
+ mutex_lock(&console_mutex);
+}
+EXPORT_SYMBOL(console_list_lock);
+
+/**
+ * console_list_unlock - Unlock the console list
+ *
+ * Counterpart to console_list_lock()
+ */
+void console_list_unlock(void)
+{
+ mutex_unlock(&console_mutex);
+}
+EXPORT_SYMBOL(console_list_unlock);
+
+/**
+ * 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.
+ * Return: A cookie to pass to console_srcu_read_unlock().
+ */
+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
+ * @cookie: cookie returned from console_srcu_read_lock()
+ *
+ * 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.
@@ -1814,13 +1897,13 @@ static void console_lock_spinning_enable(void)
* safe to start busy waiting for the lock. Second, it checks if
* there is a busy waiter and passes the lock rights to her.
*
- * Important: Callers lose the lock if there was a busy waiter.
- * They must not touch items synchronized by console_lock
- * in this case.
+ * Important: Callers lose both the console_lock and the SRCU read lock if
+ * there was a busy waiter. They must not touch items synchronized by
+ * console_lock or SRCU read lock in this case.
*
* Return: 1 if the lock rights were passed, 0 otherwise.
*/
-static int console_lock_spinning_disable_and_check(void)
+static int console_lock_spinning_disable_and_check(int cookie)
{
int waiter;
@@ -1840,6 +1923,12 @@ static int console_lock_spinning_disable_and_check(void)
spin_release(&console_owner_dep_map, _THIS_IP_);
/*
+ * Preserve lockdep lock ordering. Release the SRCU read lock before
+ * releasing the console_lock.
+ */
+ console_srcu_read_unlock(cookie);
+
+ /*
* Hand off console_lock to waiter. The waiter will perform
* the up(). After this, the waiter is the console_lock owner.
*/
@@ -2322,7 +2411,7 @@ static ssize_t msg_print_ext_body(char *buf, size_t size,
char *text, size_t text_len,
struct dev_printk_info *dev_info) { return 0; }
static void console_lock_spinning_enable(void) { }
-static int console_lock_spinning_disable_and_check(void) { return 0; }
+static int console_lock_spinning_disable_and_check(int cookie) { return 0; }
static void call_console_driver(struct console *con, const char *text, size_t len,
char *dropped_text)
{
@@ -2553,10 +2642,10 @@ 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 the console_drivers list.
+ * Acquires a lock which guarantees that no consoles will
+ * be in or enter their write() callback.
*
* Can sleep, returns nothing.
*/
@@ -2573,10 +2662,10 @@ 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 the console_drivers 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.
*/
@@ -2623,11 +2712,13 @@ static bool abandon_console_lock_in_panic(void)
* Check if the given console is currently capable and allowed to print
* records.
*
- * Requires the console_lock.
+ * Requires the console_srcu_read_lock.
*/
static inline bool console_is_usable(struct console *con)
{
- if (!(con->flags & CON_ENABLED))
+ short flags = console_srcu_read_flags(con);
+
+ if (!(flags & CON_ENABLED))
return false;
if (!con->write)
@@ -2638,8 +2729,7 @@ static inline bool console_is_usable(struct console *con)
* allocated. So unless they're explicitly marked as being able to
* cope (CON_ANYTIME) don't call them until this CPU is officially up.
*/
- if (!cpu_online(raw_smp_processor_id()) &&
- !(con->flags & CON_ANYTIME))
+ if (!cpu_online(raw_smp_processor_id()) && !(flags & CON_ANYTIME))
return false;
return true;
@@ -2664,16 +2754,18 @@ static void __console_unlock(void)
* DROPPED_TEXT_MAX. Otherwise @dropped_text must be NULL.
*
* @handover will be set to true if a printk waiter has taken over the
- * console_lock, in which case the caller is no longer holding the
- * console_lock. Otherwise it is set to false.
+ * console_lock, in which case the caller is no longer holding both the
+ * console_lock and the SRCU read lock. Otherwise it is set to false.
+ *
+ * @cookie is the cookie from the SRCU read lock.
*
* Returns false if the given console has no next record to print, otherwise
* true.
*
- * Requires the console_lock.
+ * Requires the console_lock and the SRCU read lock.
*/
static bool console_emit_next_record(struct console *con, char *text, char *ext_text,
- char *dropped_text, bool *handover)
+ char *dropped_text, bool *handover, int cookie)
{
static int panic_console_dropped;
struct printk_info info;
@@ -2733,7 +2825,7 @@ static bool console_emit_next_record(struct console *con, char *text, char *ext_
con->seq++;
- *handover = console_lock_spinning_disable_and_check();
+ *handover = console_lock_spinning_disable_and_check(cookie);
printk_safe_exit_irqrestore(flags);
skip:
return true;
@@ -2770,6 +2862,7 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove
bool any_usable = false;
struct console *con;
bool any_progress;
+ int cookie;
*next_seq = 0;
*handover = false;
@@ -2777,23 +2870,29 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove
do {
any_progress = false;
- for_each_console(con) {
+ cookie = console_srcu_read_lock();
+ for_each_console_srcu(con) {
bool progress;
if (!console_is_usable(con))
continue;
any_usable = true;
- if (con->flags & CON_EXTENDED) {
+ if (console_srcu_read_flags(con) & CON_EXTENDED) {
/* Extended consoles do not print "dropped messages". */
progress = console_emit_next_record(con, &text[0],
&ext_text[0], NULL,
- handover);
+ handover, cookie);
} else {
progress = console_emit_next_record(con, &text[0],
NULL, &dropped_text[0],
- handover);
+ handover, cookie);
}
+
+ /*
+ * If a handover has occurred, the SRCU read lock
+ * is already released.
+ */
if (*handover)
return false;
@@ -2807,21 +2906,26 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove
/* Allow panic_cpu to take over the consoles safely. */
if (abandon_console_lock_in_panic())
- return false;
+ goto abandon;
if (do_cond_resched)
cond_resched();
}
+ console_srcu_read_unlock(cookie);
} while (any_progress);
return any_usable;
+
+abandon:
+ console_srcu_read_unlock(cookie);
+ return false;
}
/**
- * 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
@@ -2899,10 +3003,14 @@ EXPORT_SYMBOL(console_conditional_schedule);
void console_unblank(void)
{
struct console *c;
+ int cookie;
/*
- * console_unblank can no longer be called in interrupt context unless
- * oops_in_progress is set to 1..
+ * Stop console printing because the unblank() callback may
+ * assume the console is not within its write() callback.
+ *
+ * If @oops_in_progress is set, this may be an atomic context.
+ * In that case, attempt a trylock as best-effort.
*/
if (oops_in_progress) {
if (down_trylock_console_sem() != 0)
@@ -2912,9 +3020,14 @@ void console_unblank(void)
console_locked = 1;
console_may_schedule = 0;
- for_each_console(c)
- if ((c->flags & CON_ENABLED) && c->unblank)
+
+ cookie = console_srcu_read_lock();
+ for_each_console_srcu(c) {
+ if ((console_srcu_read_flags(c) & CON_ENABLED) && c->unblank)
c->unblank();
+ }
+ console_srcu_read_unlock(cookie);
+
console_unlock();
if (!oops_in_progress)
@@ -2941,11 +3054,21 @@ void console_flush_on_panic(enum con_flush_mode mode)
if (mode == CONSOLE_REPLAY_ALL) {
struct console *c;
+ int cookie;
u64 seq;
seq = prb_first_valid_seq(prb);
- for_each_console(c)
+
+ cookie = console_srcu_read_lock();
+ for_each_console_srcu(c) {
+ /*
+ * If the above console_trylock() failed, this is an
+ * unsynchronized assignment. But in that case, the
+ * kernel is in "hope and pray" mode anyway.
+ */
c->seq = seq;
+ }
+ console_srcu_read_unlock(cookie);
}
console_unlock();
}
@@ -2957,15 +3080,25 @@ struct tty_driver *console_device(int *index)
{
struct console *c;
struct tty_driver *driver = NULL;
+ int cookie;
+ /*
+ * Take console_lock to serialize device() callback with
+ * other console operations. For example, fg_console is
+ * modified under console_lock when switching vt.
+ */
console_lock();
- for_each_console(c) {
+
+ cookie = console_srcu_read_lock();
+ for_each_console_srcu(c) {
if (!c->device)
continue;
driver = c->device(c, index);
if (driver)
break;
}
+ console_srcu_read_unlock(cookie);
+
console_unlock();
return driver;
}
@@ -2978,17 +3111,25 @@ struct tty_driver *console_device(int *index)
void console_stop(struct console *console)
{
__pr_flush(console, 1000, true);
- console_lock();
- console->flags &= ~CON_ENABLED;
- console_unlock();
+ console_list_lock();
+ console_srcu_write_flags(console, console->flags & ~CON_ENABLED);
+ console_list_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);
void console_start(struct console *console)
{
- console_lock();
- console->flags |= CON_ENABLED;
- console_unlock();
+ console_list_lock();
+ console_srcu_write_flags(console, console->flags | CON_ENABLED);
+ console_list_unlock();
__pr_flush(console, 1000, true);
}
EXPORT_SYMBOL(console_start);
@@ -3081,6 +3222,72 @@ static void try_enable_default_console(struct console *newcon)
(con->flags & CON_BOOT) ? "boot" : "", \
con->name, con->index, ##__VA_ARGS__)
+static void console_init_seq(struct console *newcon, bool bootcon_registered)
+{
+ struct console *con;
+ bool handover;
+
+ if (newcon->flags & (CON_PRINTBUFFER | CON_BOOT)) {
+ /* Get a consistent copy of @syslog_seq. */
+ mutex_lock(&syslog_lock);
+ newcon->seq = syslog_seq;
+ mutex_unlock(&syslog_lock);
+ } else {
+ /* Begin with next message added to ringbuffer. */
+ newcon->seq = prb_next_seq(prb);
+
+ /*
+ * If any enabled boot consoles are due to be unregistered
+ * shortly, some may not be caught up and may be the same
+ * device as @newcon. Since it is not known which boot console
+ * is the same device, flush all consoles and, if necessary,
+ * start with the message of the enabled boot console that is
+ * 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.
+ */
+ if (!console_flush_all(true, &newcon->seq, &handover)) {
+ /*
+ * Flushing failed. Just choose the lowest
+ * sequence of the enabled boot consoles.
+ */
+
+ /*
+ * If there was a handover, this context no
+ * longer holds the console_lock.
+ */
+ if (handover)
+ console_lock();
+
+ newcon->seq = prb_next_seq(prb);
+ for_each_console(con) {
+ if ((con->flags & CON_BOOT) &&
+ (con->flags & CON_ENABLED) &&
+ con->seq < newcon->seq) {
+ newcon->seq = con->seq;
+ }
+ }
+ }
+
+ console_unlock();
+ }
+ }
+}
+
+#define console_first() \
+ hlist_entry(console_list.first, struct console, node)
+
+static int unregister_console_locked(struct console *console);
+
/*
* The console driver calls this routine during kernel initialization
* to register the console printing procedure with printk() and to
@@ -3103,28 +3310,29 @@ static void try_enable_default_console(struct console *newcon)
void register_console(struct console *newcon)
{
struct console *con;
- bool bootcon_enabled = false;
- bool realcon_enabled = false;
+ bool bootcon_registered = false;
+ bool realcon_registered = false;
int err;
+ console_list_lock();
+
for_each_console(con) {
if (WARN(con == newcon, "console '%s%d' already registered\n",
- con->name, con->index))
- return;
- }
+ con->name, con->index)) {
+ goto unlock;
+ }
- for_each_console(con) {
if (con->flags & CON_BOOT)
- bootcon_enabled = true;
+ bootcon_registered = true;
else
- realcon_enabled = true;
+ realcon_registered = true;
}
/* Do not register boot consoles when there already is a real one. */
- if (newcon->flags & CON_BOOT && realcon_enabled) {
+ if ((newcon->flags & CON_BOOT) && realcon_registered) {
pr_info("Too late to register bootconsole %s%d\n",
newcon->name, newcon->index);
- return;
+ goto unlock;
}
/*
@@ -3140,8 +3348,8 @@ 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);
}
}
@@ -3155,7 +3363,7 @@ void register_console(struct console *newcon)
/* printk() messages are not printed to the Braille console. */
if (err || newcon->flags & CON_BRL)
- return;
+ goto unlock;
/*
* If we have a bootconsole, and are switching to a real console,
@@ -3163,39 +3371,38 @@ void register_console(struct console *newcon)
* the real console are the same physical device, it's annoying to
* see the beginning boot messages twice
*/
- if (bootcon_enabled &&
+ if (bootcon_registered &&
((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
newcon->flags &= ~CON_PRINTBUFFER;
}
+ newcon->dropped = 0;
+ console_init_seq(newcon, bootcon_registered);
+
/*
- * 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;
- } else {
- newcon->next = console_drivers->next;
- console_drivers->next = newcon;
- }
+ hlist_add_head_rcu(&newcon->node, &console_list);
+
+ } else if (newcon->flags & CON_CONSDEV) {
+ /* Only the new head can have CON_CONSDEV set. */
+ console_srcu_write_flags(console_first(), console_first()->flags & ~CON_CONSDEV);
+ hlist_add_head_rcu(&newcon->node, &console_list);
- newcon->dropped = 0;
- if (newcon->flags & CON_PRINTBUFFER) {
- /* Get a consistent copy of @syslog_seq. */
- mutex_lock(&syslog_lock);
- newcon->seq = syslog_seq;
- mutex_unlock(&syslog_lock);
} else {
- /* Begin with next message. */
- newcon->seq = prb_next_seq(prb);
+ 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();
/*
@@ -3206,21 +3413,28 @@ void register_console(struct console *newcon)
* went to the bootconsole (that they do not see on the real console)
*/
con_printk(KERN_INFO, newcon, "enabled\n");
- if (bootcon_enabled &&
+ if (bootcon_registered &&
((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);
+ unregister_console_locked(con);
+ }
}
+unlock:
+ console_list_unlock();
}
EXPORT_SYMBOL(register_console);
-int unregister_console(struct console *console)
+/* Must be called under console_list_lock(). */
+static int unregister_console_locked(struct console *console)
{
- struct console *con;
int res;
+ lockdep_assert_console_list_lock_held();
+
con_printk(KERN_INFO, console, "disabled\n");
res = _braille_unregister_console(console);
@@ -3229,48 +3443,94 @@ 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_srcu_write_flags(console, console->flags & ~CON_ENABLED);
+
+ if (!console_is_registered_locked(console))
+ return -ENODEV;
- if (res)
- goto out_disable_unlock;
+ hlist_del_init_rcu(&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_srcu_write_flags(console_first(), console_first()->flags | CON_CONSDEV);
+
+ /*
+ * 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->flags &= ~CON_ENABLED;
- console_unlock();
console_sysfs_notify();
if (console->exit)
res = console->exit(console);
return res;
+}
-out_disable_unlock:
- console->flags &= ~CON_ENABLED;
- console_unlock();
+int unregister_console(struct console *console)
+{
+ int res;
+ console_list_lock();
+ res = unregister_console_locked(console);
+ console_list_unlock();
return res;
}
EXPORT_SYMBOL(unregister_console);
+/**
+ * console_force_preferred_locked - force a registered console preferred
+ * @con: The registered console to force preferred.
+ *
+ * Must be called under console_list_lock().
+ */
+void console_force_preferred_locked(struct console *con)
+{
+ struct console *cur_pref_con;
+
+ if (!console_is_registered_locked(con))
+ return;
+
+ cur_pref_con = console_first();
+
+ /* Already preferred? */
+ if (cur_pref_con == con)
+ return;
+
+ /*
+ * Delete, but do not re-initialize the entry. This allows the console
+ * to continue to appear registered (via any hlist_unhashed_lockless()
+ * checks), even though it was briefly removed from the console list.
+ */
+ hlist_del_rcu(&con->node);
+
+ /*
+ * Ensure that all SRCU list walks have completed so that the console
+ * can be added to the beginning of the console list and its forward
+ * list pointer can be re-initialized.
+ */
+ synchronize_srcu(&console_srcu);
+
+ con->flags |= CON_CONSDEV;
+ WARN_ON(!con->device);
+
+ /* Only the new head can have CON_CONSDEV set. */
+ console_srcu_write_flags(cur_pref_con, cur_pref_con->flags & ~CON_CONSDEV);
+ hlist_add_head_rcu(&con->node, &console_list);
+}
+EXPORT_SYMBOL(console_force_preferred_locked);
+
/*
* Initialize the console device. This is called *early*, so
* we can't necessarily depend on lots of kernel help here.
@@ -3317,10 +3577,12 @@ 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) {
+ console_list_lock();
+ hlist_for_each_entry_safe(con, tmp, &console_list, node) {
if (!(con->flags & CON_BOOT))
continue;
@@ -3337,9 +3599,11 @@ static int __init printk_late_init(void)
*/
pr_warn("bootconsole [%s%d] uses init memory and must be disabled even before the real one is ready\n",
con->name, con->index);
- unregister_console(con);
+ unregister_console_locked(con);
}
}
+ console_list_unlock();
+
ret = cpuhp_setup_state_nocalls(CPUHP_PRINTK_DEAD, "printk:dead", NULL,
console_cpu_notify);
WARN_ON(ret < 0);
@@ -3359,6 +3623,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
struct console *c;
u64 last_diff = 0;
u64 printk_seq;
+ int cookie;
u64 diff;
u64 seq;
@@ -3369,9 +3634,15 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
for (;;) {
diff = 0;
+ /*
+ * Hold the console_lock to guarantee safe access to
+ * console->seq and to prevent changes to @console_suspended
+ * until all consoles have been processed.
+ */
console_lock();
- for_each_console(c) {
+ cookie = console_srcu_read_lock();
+ for_each_console_srcu(c) {
if (con && con != c)
continue;
if (!console_is_usable(c))
@@ -3380,6 +3651,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
if (printk_seq < seq)
diff += seq - printk_seq;
}
+ console_srcu_read_unlock(cookie);
/*
* If consoles are suspended, it cannot be expected that they