diff options
Diffstat (limited to 'kernel/printk/printk.c')
| -rw-r--r-- | kernel/printk/printk.c | 587 |
1 files changed, 63 insertions, 524 deletions
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index ea3dd55709e7..b49c6ff6dca0 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -224,33 +224,6 @@ int devkmsg_sysctl_set_loglvl(struct ctl_table *table, int write, static int nr_ext_console_drivers; /* - * Used to synchronize printing kthreads against direct printing via - * console_trylock/console_unlock. - * - * Values: - * -1 = console kthreads atomically blocked (via global trylock) - * 0 = no kthread printing, console not locked (via trylock) - * >0 = kthread(s) actively printing - * - * Note: For synchronizing against direct printing via - * console_lock/console_unlock, see the @lock variable in - * struct console. - */ -static atomic_t console_kthreads_active = ATOMIC_INIT(0); - -#define console_kthreads_atomic_tryblock() \ - (atomic_cmpxchg(&console_kthreads_active, 0, -1) == 0) -#define console_kthreads_atomic_unblock() \ - atomic_cmpxchg(&console_kthreads_active, -1, 0) -#define console_kthreads_atomically_blocked() \ - (atomic_read(&console_kthreads_active) == -1) - -#define console_kthread_printing_tryenter() \ - atomic_inc_unless_negative(&console_kthreads_active) -#define console_kthread_printing_exit() \ - atomic_dec(&console_kthreads_active) - -/* * Helper macros to handle lockdep when locking/unlocking console_sem. We use * macros instead of functions so that _RET_IP_ contains useful information. */ @@ -298,49 +271,14 @@ static bool panic_in_progress(void) } /* - * Tracks whether kthread printers are all blocked. A value of true implies - * that the console is locked via console_lock() or the console is suspended. - * Writing to this variable requires holding @console_sem. + * This is used for debugging the mess that is the VT code by + * keeping track if we have the console semaphore held. It's + * definitely not the perfect debug tool (we don't know if _WE_ + * hold it and are racing, but it helps tracking those weird code + * paths in the console code where we end up in places I want + * locked without the console semaphore held). */ -static bool console_kthreads_blocked; - -/* - * Block all kthread printers from a schedulable context. - * - * Requires holding @console_sem. - */ -static void console_kthreads_block(void) -{ - struct console *con; - - for_each_console(con) { - mutex_lock(&con->lock); - con->blocked = true; - mutex_unlock(&con->lock); - } - - console_kthreads_blocked = true; -} - -/* - * Unblock all kthread printers from a schedulable context. - * - * Requires holding @console_sem. - */ -static void console_kthreads_unblock(void) -{ - struct console *con; - - for_each_console(con) { - mutex_lock(&con->lock); - con->blocked = false; - mutex_unlock(&con->lock); - } - - console_kthreads_blocked = false; -} - -static int console_suspended; +static int console_locked, console_suspended; /* * Array of consoles built from command line options (console=) @@ -423,75 +361,7 @@ static int console_msg_format = MSG_FORMAT_DEFAULT; /* 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); - -/** - * printk_prefer_direct_enter - cause printk() calls to attempt direct - * printing to all enabled consoles - * - * Since it is not possible to call into the console printing code from any - * context, there is no guarantee that direct printing will occur. - * - * This globally effects all printk() callers. - * - * Context: Any context. - */ -void printk_prefer_direct_enter(void) -{ - atomic_inc(&printk_prefer_direct); -} - -/** - * printk_prefer_direct_exit - restore printk() behavior - * - * Context: Any context. - */ -void printk_prefer_direct_exit(void) -{ - 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 */ @@ -2382,10 +2252,10 @@ asmlinkage int vprintk_emit(int facility, int level, 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. @@ -2428,8 +2298,6 @@ EXPORT_SYMBOL(_printk); 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 @@ -2463,8 +2331,6 @@ static void call_console_driver(struct console *con, const char *text, size_t le } 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 */ @@ -2683,14 +2549,6 @@ static int console_cpu_notify(unsigned int cpu) /* If trylock fails, someone else is doing the printing */ if (console_trylock()) console_unlock(); - else { - /* - * If a new CPU comes online, the conditions for - * printer_should_wake() may have changed for some - * kthread printer with !CON_ANYTIME. - */ - wake_up_klogd(); - } } return 0; } @@ -2710,7 +2568,7 @@ void console_lock(void) down_console_sem(); if (console_suspended) return; - console_kthreads_block(); + console_locked = 1; console_may_schedule = 1; } EXPORT_SYMBOL(console_lock); @@ -2731,30 +2589,15 @@ int console_trylock(void) up_console_sem(); return 0; } - if (!console_kthreads_atomic_tryblock()) { - up_console_sem(); - return 0; - } + console_locked = 1; console_may_schedule = 0; return 1; } EXPORT_SYMBOL(console_trylock); -/* - * This is used to help to make sure that certain paths within the VT code are - * running with the console lock held. It is definitely not the perfect debug - * tool (it is not known if the VT code is the task holding the console lock), - * but it helps tracking those weird code paths in the console code such as - * when the console is suspended: where the console is not locked but no - * console printing may occur. - * - * Note: This returns true when the console is suspended but is not locked. - * This is intentional because the VT code must consider that situation - * the same as if the console was locked. - */ int is_console_locked(void) { - return (console_kthreads_blocked || atomic_read(&console_kthreads_active)); + return console_locked; } EXPORT_SYMBOL(is_console_locked); @@ -2777,9 +2620,18 @@ static bool abandon_console_lock_in_panic(void) 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; /* @@ -2788,43 +2640,15 @@ static inline bool __console_is_usable(short flags) * 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 holding 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) { - /* - * Depending on whether console_lock() or console_trylock() was used, - * appropriately allow the kthread printers to continue. - */ - if (console_kthreads_blocked) - console_kthreads_unblock(); - else - console_kthreads_atomic_unblock(); - - /* - * New records may have arrived while the console was locked. - * Wake the kthread printers to print them. - */ - wake_up_klogd(); - + console_locked = 0; up_console_sem(); } @@ -2842,19 +2666,17 @@ static void __console_unlock(void) * * @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. A NULL pointer may be provided - * to disable allowing the console_lock to be taken over by a printk waiter. + * console_lock. Otherwise it is set to false. * * Returns false if the given console has no next record to print, otherwise * true. * - * Requires the console_lock if @handover is non-NULL. - * Requires con->lock otherwise. + * Requires the console_lock. */ -static bool __console_emit_next_record(struct console *con, char *text, char *ext_text, - char *dropped_text, bool *handover) +static bool console_emit_next_record(struct console *con, char *text, char *ext_text, + char *dropped_text, bool *handover) { - static atomic_t panic_console_dropped = ATOMIC_INIT(0); + static int panic_console_dropped; struct printk_info info; struct printk_record r; unsigned long flags; @@ -2863,8 +2685,7 @@ static bool __console_emit_next_record(struct console *con, char *text, char *ex prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX); - if (handover) - *handover = false; + *handover = false; if (!prb_read_valid(prb, con->seq, &r)) return false; @@ -2872,8 +2693,7 @@ static bool __console_emit_next_record(struct console *con, char *text, char *ex if (con->seq != r.info->seq) { con->dropped += r.info->seq - con->seq; con->seq = r.info->seq; - if (panic_in_progress() && - atomic_fetch_inc_relaxed(&panic_console_dropped) > 10) { + if (panic_in_progress() && panic_console_dropped++ > 10) { suppress_panic_printk = 1; pr_warn_once("Too many dropped messages. Suppress messages on non-panic CPUs to prevent livelock.\n"); } @@ -2895,62 +2715,32 @@ static bool __console_emit_next_record(struct console *con, char *text, char *ex len = record_print_text(&r, console_msg_format & MSG_FORMAT_SYSLOG, printk_time); } - if (handover) { - /* - * While actively printing out messages, if another printk() - * were to occur on another CPU, it may wait for this one to - * finish. This task can not be preempted if there is a - * waiter waiting to take over. - * - * Interrupts are disabled because the hand over to a waiter - * must not be interrupted until the hand over is completed - * (@console_waiter is cleared). - */ - printk_safe_enter_irqsave(flags); - console_lock_spinning_enable(); - - /* don't trace irqsoff print latency */ - stop_critical_timings(); - } + /* + * While actively printing out messages, if another printk() + * were to occur on another CPU, it may wait for this one to + * finish. This task can not be preempted if there is a + * waiter waiting to take over. + * + * Interrupts are disabled because the hand over to a waiter + * must not be interrupted until the hand over is completed + * (@console_waiter is cleared). + */ + printk_safe_enter_irqsave(flags); + console_lock_spinning_enable(); + stop_critical_timings(); /* don't trace print latency */ call_console_driver(con, write_text, len, dropped_text); + start_critical_timings(); con->seq++; - if (handover) { - start_critical_timings(); - *handover = console_lock_spinning_disable_and_check(); - printk_safe_exit_irqrestore(flags); - } + *handover = console_lock_spinning_disable_and_check(); + printk_safe_exit_irqrestore(flags); skip: return true; } /* - * Print a record for a given console, but allow another printk() caller to - * take over the console_lock and continue printing. - * - * Requires the console_lock, but depending on @handover after the call, the - * caller may no longer have the console_lock. - * - * See __console_emit_next_record() for argument and return details. - */ -static bool console_emit_next_record_transferable(struct console *con, char *text, char *ext_text, - char *dropped_text, bool *handover) -{ - /* - * Handovers are only supported if threaded printers are atomically - * blocked. The context taking over the console_lock may be atomic. - */ - if (!console_kthreads_atomically_blocked()) { - *handover = false; - handover = NULL; - } - - return __console_emit_next_record(con, text, ext_text, dropped_text, handover); -} - -/* * Print out all remaining records to all consoles. * * @do_cond_resched is set by the caller. It can be true only in schedulable @@ -2968,8 +2758,8 @@ static bool console_emit_next_record_transferable(struct console *con, char *tex * 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. */ @@ -2986,10 +2776,6 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove *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) { @@ -3001,11 +2787,13 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove if (con->flags & CON_EXTENDED) { /* Extended consoles do not print "dropped messages". */ - progress = console_emit_next_record_transferable(con, &text[0], - &ext_text[0], NULL, handover); + progress = console_emit_next_record(con, &text[0], + &ext_text[0], NULL, + handover); } else { - progress = console_emit_next_record_transferable(con, &text[0], - NULL, &dropped_text[0], handover); + progress = console_emit_next_record(con, &text[0], + NULL, &dropped_text[0], + handover); } if (*handover) return false; @@ -3120,13 +2908,10 @@ void console_unblank(void) if (oops_in_progress) { if (down_trylock_console_sem() != 0) return; - if (!console_kthreads_atomic_tryblock()) { - up_console_sem(); - return; - } } else console_lock(); + console_locked = 1; console_may_schedule = 0; for_each_console(c) if ((c->flags & CON_ENABLED) && c->unblank) @@ -3405,10 +3190,6 @@ void register_console(struct console *newcon) nr_ext_console_drivers++; newcon->dropped = 0; - newcon->thread = NULL; - newcon->blocked = true; - mutex_init(&newcon->lock); - if (newcon->flags & CON_PRINTBUFFER) { /* Get a consistent copy of @syslog_seq. */ mutex_lock(&syslog_lock); @@ -3418,10 +3199,6 @@ void register_console(struct console *newcon) /* Begin with next message. */ newcon->seq = prb_next_seq(prb); } - - if (printk_kthreads_available) - printk_start_kthread(newcon); - console_unlock(); console_sysfs_notify(); @@ -3448,7 +3225,6 @@ EXPORT_SYMBOL(register_console); int unregister_console(struct console *console) { - struct task_struct *thd; struct console *con; int res; @@ -3489,20 +3265,7 @@ int unregister_console(struct console *console) 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) @@ -3598,20 +3361,6 @@ static int __init printk_late_init(void) } 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) @@ -3686,206 +3435,11 @@ bool pr_flush(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(); -} - -/* - * Print a record for a given console, not allowing another printk() caller - * to take over. This is appropriate for contexts that do not have the - * console_lock. - * - * See __console_emit_next_record() for argument and return details. - */ -static bool console_emit_next_record(struct console *con, char *text, char *ext_text, - char *dropped_text) -{ - return __console_emit_next_record(con, text, ext_text, dropped_text, NULL); -} - -static bool printer_should_wake(struct console *con, u64 seq) -{ - short flags; - - if (kthread_should_stop() || !printk_kthreads_available) - return true; - - if (con->blocked || - console_kthreads_atomically_blocked()) { - 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; - 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; - - error = mutex_lock_interruptible(&con->lock); - if (error) - continue; - - if (con->blocked || - !console_kthread_printing_tryenter()) { - /* Another context has locked the console_lock. */ - mutex_unlock(&con->lock); - continue; - } - - /* - * Although this context has not locked the console_lock, it - * is known that the console_lock is not locked and it is not - * possible for any other context to lock the console_lock. - * Therefore it is safe to read con->flags. - */ - - if (!__console_is_usable(con->flags)) { - console_kthread_printing_exit(); - mutex_unlock(&con->lock); - 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); - - seq = con->seq; - - console_kthread_printing_exit(); - - mutex_unlock(&con->lock); - } - - 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); @@ -3893,14 +3447,10 @@ static void wake_up_klogd_work_func(struct irq_work *irq_work) { 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) @@ -3925,11 +3475,10 @@ static void __wake_up_klogd(int val) * 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)); } @@ -3947,17 +3496,7 @@ void defer_console_output(void) * 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) |