/* syslog_lock protects syslog_* variables and write access to clear_seq. */
static DEFINE_MUTEX(syslog_lock);
-/*
- * A flag to signify if printk_activate_kthreads() has already started the
- * kthread printers. If true, any later registered consoles must start their
- * own kthread directly. The flag is write protected by the console_lock.
- */
-static bool printk_kthreads_available;
-
#ifdef CONFIG_PRINTK
static atomic_t printk_prefer_direct = ATOMIC_INIT(0);
WARN_ON(atomic_dec_if_positive(&printk_prefer_direct) < 0);
}
-/*
- * Calling printk() always wakes kthread printers so that they can
- * flush the new message to their respective consoles. Also, if direct
- * printing is allowed, printk() tries to flush the messages directly.
- *
- * Direct printing is allowed in situations when the kthreads
- * are not available or the system is in a problematic state.
- *
- * See the implementation about possible races.
- */
-static inline bool allow_direct_printing(void)
-{
- /*
- * Checking kthread availability is a possible race because the
- * kthread printers can become permanently disabled during runtime.
- * However, doing that requires holding the console_lock, so any
- * pending messages will be direct printed by console_unlock().
- */
- if (!printk_kthreads_available)
- return true;
-
- /*
- * Prefer direct printing when the system is in a problematic state.
- * The context that sets this state will always see the updated value.
- * The other contexts do not care. Anyway, direct printing is just a
- * best effort. The direct output is only possible when console_lock
- * is not already taken and no kthread printers are actively printing.
- */
- return (system_state > SYSTEM_RUNNING ||
- oops_in_progress ||
- atomic_read(&printk_prefer_direct));
-}
-
DECLARE_WAIT_QUEUE_HEAD(log_wait);
/* All 3 protected by @syslog_lock. */
/* the next printk record to read by syslog(READ) or /proc/kmsg */
printed_len = vprintk_store(facility, level, dev_info, fmt, args);
/* If called from the scheduler, we can not call up(). */
- if (!in_sched && allow_direct_printing()) {
+ if (!in_sched) {
/*
* The caller may be holding system-critical or
- * timing-sensitive locks. Disable preemption during direct
+ * timing-sensitive locks. Disable preemption during
* printing of all remaining records to all consoles so that
* this context can return as soon as possible. Hopefully
* another printk() caller will take over the printing.
static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress);
-static void printk_start_kthread(struct console *con);
-
#else /* CONFIG_PRINTK */
#define CONSOLE_LOG_MAX 0
}
static bool suppress_message_printing(int level) { return false; }
static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress) { return true; }
-static void printk_start_kthread(struct console *con) { }
-static bool allow_direct_printing(void) { return true; }
#endif /* CONFIG_PRINTK */
down_console_sem();
console_suspended = 0;
console_unlock();
-
- /*
- * While suspended, new records may have been added to the
- * ringbuffer. Wake up the kthread printers to print them.
- */
- wake_up_klogd();
-
pr_flush(1000, true);
}
/* If trylock fails, someone else is doing the printing */
if (console_trylock())
console_unlock();
-
- /* Wake kthread printers. Some may have become usable. */
- wake_up_klogd();
}
return 0;
}
return atomic_read(&panic_cpu) != raw_smp_processor_id();
}
-static inline bool __console_is_usable(short flags)
+/*
+ * Check if the given console is currently capable and allowed to print
+ * records.
+ *
+ * Requires the console_lock.
+ */
+static inline bool console_is_usable(struct console *con)
{
- if (!(flags & CON_ENABLED))
+ if (!(con->flags & CON_ENABLED))
+ return false;
+
+ if (!con->write)
return false;
/*
* cope (CON_ANYTIME) don't call them until this CPU is officially up.
*/
if (!cpu_online(raw_smp_processor_id()) &&
- !(flags & CON_ANYTIME))
+ !(con->flags & CON_ANYTIME))
return false;
return true;
}
-/*
- * Check if the given console is currently capable and allowed to print
- * records.
- *
- * Requires the console_lock.
- */
-static inline bool console_is_usable(struct console *con)
-{
- if (!con->write)
- return false;
-
- return __console_is_usable(con->flags);
-}
-
static void __console_unlock(void)
{
console_locked = 0;
* were flushed to all usable consoles. A returned false informs the caller
* that everything was not flushed (either there were no usable consoles or
* another context has taken over printing or it is a panic situation and this
- * is not the panic CPU or direct printing is not preferred). Regardless the
- * reason, the caller should assume it is not useful to immediately try again.
+ * is not the panic CPU). Regardless the reason, the caller should assume it
+ * is not useful to immediately try again.
*
* Requires the console_lock.
*/
*handover = false;
do {
- /* Let the kthread printers do the work if they can. */
- if (!allow_direct_printing())
- return false;
-
any_progress = false;
for_each_console(con) {
console_lock();
console->flags |= CON_ENABLED;
console_unlock();
-
- /* Wake the newly enabled kthread printer. */
- wake_up_klogd();
-
__pr_flush(console, 1000, true);
}
EXPORT_SYMBOL(console_start);
nr_ext_console_drivers++;
newcon->dropped = 0;
- newcon->thread = NULL;
-
if (newcon->flags & CON_PRINTBUFFER) {
/* Get a consistent copy of @syslog_seq. */
mutex_lock(&syslog_lock);
/* Begin with next message. */
newcon->seq = prb_next_seq(prb);
}
-
- if (printk_kthreads_available)
- printk_start_kthread(newcon);
-
console_unlock();
console_sysfs_notify();
int unregister_console(struct console *console)
{
- struct task_struct *thd;
struct console *con;
int res;
console_drivers->flags |= CON_CONSDEV;
console->flags &= ~CON_ENABLED;
-
- /*
- * console->thread can only be cleared under the console lock. But
- * stopping the thread must be done without the console lock. The
- * task that clears @thread is the task that stops the kthread.
- */
- thd = console->thread;
- console->thread = NULL;
-
console_unlock();
-
- if (thd)
- kthread_stop(thd);
-
console_sysfs_notify();
if (console->exit)
}
late_initcall(printk_late_init);
-static int __init printk_activate_kthreads(void)
-{
- struct console *con;
-
- console_lock();
- printk_kthreads_available = true;
- for_each_console(con)
- printk_start_kthread(con);
- console_unlock();
-
- return 0;
-}
-early_initcall(printk_activate_kthreads);
-
#if defined CONFIG_PRINTK
/* If @con is specified, only wait for that console. Otherwise wait for all. */
static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress)
}
EXPORT_SYMBOL(pr_flush);
-static void __printk_fallback_preferred_direct(void)
-{
- printk_prefer_direct_enter();
- pr_err("falling back to preferred direct printing\n");
- printk_kthreads_available = false;
-}
-
-/*
- * Enter preferred direct printing, but never exit. Mark console threads as
- * unavailable. The system is then forever in preferred direct printing and
- * any printing threads will exit.
- *
- * Must *not* be called under console_lock. Use
- * __printk_fallback_preferred_direct() if already holding console_lock.
- */
-static void printk_fallback_preferred_direct(void)
-{
- console_lock();
- __printk_fallback_preferred_direct();
- console_unlock();
-}
-
-static bool printer_should_wake(struct console *con, u64 seq)
-{
- short flags;
-
- if (kthread_should_stop() || !printk_kthreads_available)
- return true;
-
- if (console_suspended)
- return false;
-
- /*
- * This is an unsafe read from con->flags, but a false positive is
- * not a problem. Worst case it would allow the printer to wake up
- * although it is disabled. But the printer will notice that when
- * attempting to print and instead go back to sleep.
- */
- flags = data_race(READ_ONCE(con->flags));
-
- if (!__console_is_usable(flags))
- return false;
-
- return prb_read_valid(prb, seq, NULL);
-}
-
-static int printk_kthread_func(void *data)
-{
- struct console *con = data;
- char *dropped_text = NULL;
- char *ext_text = NULL;
- bool handover;
- u64 seq = 0;
- char *text;
- int error;
-
- text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL);
- if (!text) {
- con_printk(KERN_ERR, con, "failed to allocate text buffer\n");
- printk_fallback_preferred_direct();
- goto out;
- }
-
- if (con->flags & CON_EXTENDED) {
- ext_text = kmalloc(CONSOLE_EXT_LOG_MAX, GFP_KERNEL);
- if (!ext_text) {
- con_printk(KERN_ERR, con, "failed to allocate ext_text buffer\n");
- printk_fallback_preferred_direct();
- goto out;
- }
- } else {
- dropped_text = kmalloc(DROPPED_TEXT_MAX, GFP_KERNEL);
- if (!dropped_text) {
- con_printk(KERN_ERR, con, "failed to allocate dropped_text buffer\n");
- printk_fallback_preferred_direct();
- goto out;
- }
- }
-
- con_printk(KERN_INFO, con, "printing thread started\n");
-
- for (;;) {
- /*
- * Guarantee this task is visible on the waitqueue before
- * checking the wake condition.
- *
- * The full memory barrier within set_current_state() of
- * prepare_to_wait_event() pairs with the full memory barrier
- * within wq_has_sleeper().
- *
- * This pairs with __wake_up_klogd:A.
- */
- error = wait_event_interruptible(log_wait,
- printer_should_wake(con, seq)); /* LMM(printk_kthread_func:A) */
-
- if (kthread_should_stop() || !printk_kthreads_available)
- break;
-
- if (error)
- continue;
-
- console_lock();
-
- if (console_suspended) {
- up_console_sem();
- continue;
- }
-
- if (!console_is_usable(con)) {
- __console_unlock();
- continue;
- }
-
- /*
- * Even though the printk kthread is always preemptible, it is
- * still not allowed to call cond_resched() from within
- * console drivers. The task may become non-preemptible in the
- * console driver call chain. For example, vt_console_print()
- * takes a spinlock and then can call into fbcon_redraw(),
- * which can conditionally invoke cond_resched().
- */
- console_may_schedule = 0;
- console_emit_next_record(con, text, ext_text, dropped_text, &handover);
- if (handover)
- continue;
-
- seq = con->seq;
-
- __console_unlock();
- }
-
- con_printk(KERN_INFO, con, "printing thread stopped\n");
-out:
- kfree(dropped_text);
- kfree(ext_text);
- kfree(text);
-
- console_lock();
- /*
- * If this kthread is being stopped by another task, con->thread will
- * already be NULL. That is fine. The important thing is that it is
- * NULL after the kthread exits.
- */
- con->thread = NULL;
- console_unlock();
-
- return 0;
-}
-
-/* Must be called under console_lock. */
-static void printk_start_kthread(struct console *con)
-{
- /*
- * Do not start a kthread if there is no write() callback. The
- * kthreads assume the write() callback exists.
- */
- if (!con->write)
- return;
-
- con->thread = kthread_run(printk_kthread_func, con,
- "pr/%s%d", con->name, con->index);
- if (IS_ERR(con->thread)) {
- con->thread = NULL;
- con_printk(KERN_ERR, con, "unable to start printing thread\n");
- __printk_fallback_preferred_direct();
- return;
- }
-}
-
/*
* Delayed printk version, for scheduler-internal messages:
*/
-#define PRINTK_PENDING_WAKEUP 0x01
-#define PRINTK_PENDING_DIRECT_OUTPUT 0x02
+#define PRINTK_PENDING_WAKEUP 0x01
+#define PRINTK_PENDING_OUTPUT 0x02
static DEFINE_PER_CPU(int, printk_pending);
{
int pending = this_cpu_xchg(printk_pending, 0);
- if (pending & PRINTK_PENDING_DIRECT_OUTPUT) {
- printk_prefer_direct_enter();
-
+ if (pending & PRINTK_PENDING_OUTPUT) {
/* If trylock fails, someone else is doing the printing */
if (console_trylock())
console_unlock();
-
- printk_prefer_direct_exit();
}
if (pending & PRINTK_PENDING_WAKEUP)
* prepare_to_wait_event(), which is called after ___wait_event() adds
* the waiter but before it has checked the wait condition.
*
- * This pairs with devkmsg_read:A, syslog_print:A, and
- * printk_kthread_func:A.
+ * This pairs with devkmsg_read:A and syslog_print:A.
*/
if (wq_has_sleeper(&log_wait) || /* LMM(__wake_up_klogd:A) */
- (val & PRINTK_PENDING_DIRECT_OUTPUT)) {
+ (val & PRINTK_PENDING_OUTPUT)) {
this_cpu_or(printk_pending, val);
irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
}
* New messages may have been added directly to the ringbuffer
* using vprintk_store(), so wake any waiters as well.
*/
- int val = PRINTK_PENDING_WAKEUP;
-
- /*
- * Make sure that some context will print the messages when direct
- * printing is allowed. This happens in situations when the kthreads
- * may not be as reliable or perhaps unusable.
- */
- if (allow_direct_printing())
- val |= PRINTK_PENDING_DIRECT_OUTPUT;
-
- __wake_up_klogd(val);
+ __wake_up_klogd(PRINTK_PENDING_WAKEUP | PRINTK_PENDING_OUTPUT);
}
void printk_trigger_flush(void)
projects / kernel.git / commitdiff