1 // SPDX-License-Identifier: GPL-2.0-only
10  * to the console.  Added hook for sending the console messages
11  * elsewhere, in preparation for a serial line console (someday).
26 #include <linux/console.h>
75 EXPORT_TRACEPOINT_SYMBOL_GPL(console);
85  * console_mutex protects console_list updates and console->flags updates.
87  * accessible via the console list.
92  * console_sem protects updates to console->seq
93  * and also provides serialization for console printing.
148 		return -EINVAL;  in __control_devkmsg()
168 	return -EINVAL;  in __control_devkmsg()
210 			return -EINVAL;  in devkmsg_sysctl_set_loglvl()
233 			return -EINVAL;  in devkmsg_sysctl_set_loglvl()
242  * console_list_lock - Lock the console list
244  * For console list or console->flags updates
254 	 * Detecting if this context is really in the read-side critical  in console_list_lock()
266  * console_list_unlock - Unlock the console list
277  * console_srcu_read_lock - Register a new reader for the
278  *	SRCU-protected console list
280  * Use for_each_console_srcu() to iterate the console list
293  * console_srcu_read_unlock - Unregister an old reader from
294  *	the SRCU-protected console list
322 	 * because spindump/WARN/etc from under console ->lock will  in __down_trylock_console_sem()
323 	 * deadlock in printk()->down_trylock_console_sem() otherwise.  in __down_trylock_console_sem()
378  * keeping track if we have the console semaphore held. It's
381  * paths in the console code where we end up in places I want
382  * locked without the console semaphore held).
387  *	Array of consoles built from command line options (console=)
394 static int preferred_console = -1;
398 /* Flag: console code may call schedule() */
411  * own meta-data (@info).
413  * Every record meta-data carries the timestamp in microseconds, as well as
415  * messages use LOG_KERN; userspace-injected messages always carry a matching
424  * pairs), to provide userspace with a machine-readable message context.
426  * Examples for well-defined, commonly used property names are:
432  *   SUBSYSTEM=pci              driver-core subsystem name
434  * Valid characters in property names are [a-zA-Z0-9.-_]. Property names
450  * userspace, it is a kernel-private implementation detail that might
461  * non-prinatable characters are escaped in the "\xff" notation.
468  * Specifies if a legacy console is registered. If legacy consoles are
469  * present, it is necessary to perform the console lock/unlock dance
470  * whenever console flushing should occur.
475  * Specifies if an nbcon console is registered. If nbcon consoles are present,
482  * Specifies if a boot console is registered. If boot consoles are present,
484  * the console lock. This is because boot consoles and nbcon consoles may
532  * Define the average message size. This only affects the number of
541 _DEFINE_PRINTKRB(printk_rb_static, CONFIG_LOG_BUF_SHIFT - PRB_AVGBITS,
549  * We cannot access per-CPU data (e.g. per-CPU flush irq_work) before
551  * it's safe to access per-CPU data.
563 	write_seqcount_latch_begin(&ls->latch);  in latched_seq_write()
564 	ls->val[0] = val;  in latched_seq_write()
565 	write_seqcount_latch(&ls->latch);  in latched_seq_write()
566 	ls->val[1] = val;  in latched_seq_write()
567 	write_seqcount_latch_end(&ls->latch);  in latched_seq_write()
578 		seq = read_seqcount_latch(&ls->latch);  in latched_seq_read_nolock()
580 		val = ls->val[idx];  in latched_seq_read_nolock()
581 	} while (read_seqcount_latch_retry(&ls->latch, seq));  in latched_seq_read_nolock()
592 /* Return log buffer size */
620 		*text_len -= *trunc_msg_len;  in truncate_msg()
632 	 * Unless restricted, we allow "read all" and "get buffer size"  in syslog_action_restricted()
651 		return -EPERM;  in check_syslog_permissions()
663 static ssize_t info_print_ext_header(char *buf, size_t size,  in info_print_ext_header()  argument
666 	u64 ts_usec = info->ts_nsec;  in info_print_ext_header()
669 	u32 id = info->caller_id;  in info_print_ext_header()
679 	return scnprintf(buf, size, "%u,%llu,%llu,%c%s;",  in info_print_ext_header()
680 			 (info->facility << 3) | info->level, info->seq,  in info_print_ext_header()
681 			 ts_usec, info->flags & LOG_CONT ? 'c' : '-', caller);  in info_print_ext_header()
684 static ssize_t msg_add_ext_text(char *buf, size_t size,  in msg_add_ext_text()  argument
688 	char *p = buf, *e = buf + size;  in msg_add_ext_text()
691 	/* escape non-printable characters */  in msg_add_ext_text()
696 			p += scnprintf(p, e - p, "\\x%02x", c);  in msg_add_ext_text()
702 	return p - buf;  in msg_add_ext_text()
705 static ssize_t msg_add_dict_text(char *buf, size_t size,  in msg_add_dict_text()  argument
714 	len = msg_add_ext_text(buf, size, "", 0, ' ');	/* dict prefix */  in msg_add_dict_text()
715 	len += msg_add_ext_text(buf + len, size - len, key, strlen(key), '=');  in msg_add_dict_text()
716 	len += msg_add_ext_text(buf + len, size - len, val, val_len, '\n');  in msg_add_dict_text()
721 static ssize_t msg_print_ext_body(char *buf, size_t size,  in msg_print_ext_body()  argument
727 	len = msg_add_ext_text(buf, size, text, text_len, '\n');  in msg_print_ext_body()
732 	len += msg_add_dict_text(buf + len, size - len, "SUBSYSTEM",  in msg_print_ext_body()
733 				 dev_info->subsystem);  in msg_print_ext_body()
734 	len += msg_add_dict_text(buf + len, size - len, "DEVICE",  in msg_print_ext_body()
735 				 dev_info->device);  in msg_print_ext_body()
740 /* /dev/kmsg - userspace message inject/listen interface */
766 	struct file *file = iocb->ki_filp;  in devkmsg_write()
767 	struct devkmsg_user *user = file->private_data;  in devkmsg_write()
772 		return -EINVAL;  in devkmsg_write()
780 		if (!___ratelimit(&user->rs, current->comm))  in devkmsg_write()
786 		return -ENOMEM;  in devkmsg_write()
791 		return -EFAULT;  in devkmsg_write()
795 	 * Extract and skip the syslog prefix <[0-9]*>. Coming from userspace  in devkmsg_write()
801 	 * kernel-generated messages from userspace-injected ones.  in devkmsg_write()
826 	struct devkmsg_user *user = file->private_data;  in devkmsg_read()
827 	char *outbuf = &user->pbufs.outbuf[0];  in devkmsg_read()
829 		.pbufs = &user->pbufs,  in devkmsg_read()
833 	ret = mutex_lock_interruptible(&user->lock);  in devkmsg_read()
837 	if (!printk_get_next_message(&pmsg, atomic64_read(&user->seq), true, false)) {  in devkmsg_read()
838 		if (file->f_flags & O_NONBLOCK) {  in devkmsg_read()
839 			ret = -EAGAIN;  in devkmsg_read()
854 				printk_get_next_message(&pmsg, atomic64_read(&user->seq), true,  in devkmsg_read()
862 		atomic64_set(&user->seq, pmsg.seq);  in devkmsg_read()
863 		ret = -EPIPE;  in devkmsg_read()
867 	atomic64_set(&user->seq, pmsg.seq + 1);  in devkmsg_read()
870 		ret = -EINVAL;  in devkmsg_read()
875 		ret = -EFAULT;  in devkmsg_read()
880 	mutex_unlock(&user->lock);  in devkmsg_read()
888  * entire variable length messages (records). Non-standard values are
894 	struct devkmsg_user *user = file->private_data;  in devkmsg_llseek()
898 		return -ESPIPE;  in devkmsg_llseek()
903 		atomic64_set(&user->seq, prb_first_valid_seq(prb));  in devkmsg_llseek()
908 		 * like issued by 'dmesg -c'. Reading /dev/kmsg itself  in devkmsg_llseek()
911 		atomic64_set(&user->seq, latched_seq_read_nolock(&clear_seq));  in devkmsg_llseek()
915 		atomic64_set(&user->seq, prb_next_seq(prb));  in devkmsg_llseek()
918 		ret = -EINVAL;  in devkmsg_llseek()
925 	struct devkmsg_user *user = file->private_data;  in devkmsg_poll()
931 	if (prb_read_valid_info(prb, atomic64_read(&user->seq), &info, NULL)) {  in devkmsg_poll()
933 		if (info.seq != atomic64_read(&user->seq))  in devkmsg_poll()
948 		return -EPERM;  in devkmsg_open()
950 	/* write-only does not need any file context */  in devkmsg_open()
951 	if ((file->f_flags & O_ACCMODE) != O_WRONLY) {  in devkmsg_open()
960 		return -ENOMEM;  in devkmsg_open()
962 	ratelimit_default_init(&user->rs);  in devkmsg_open()
963 	ratelimit_set_flags(&user->rs, RATELIMIT_MSG_ON_RELEASE);  in devkmsg_open()
965 	mutex_init(&user->lock);  in devkmsg_open()
967 	atomic64_set(&user->seq, prb_first_valid_seq(prb));  in devkmsg_open()
969 	file->private_data = user;  in devkmsg_open()
975 	struct devkmsg_user *user = file->private_data;  in devkmsg_release()
977 	ratelimit_state_exit(&user->rs);  in devkmsg_release()
979 	mutex_destroy(&user->lock);  in devkmsg_release()
1011 	 * Export struct size and field offsets. User space tools can  in log_buf_vmcoreinfo_setup()
1044 	VMCOREINFO_LENGTH(printk_info_subsystem, sizeof(dev_info->subsystem));  in log_buf_vmcoreinfo_setup()
1046 	VMCOREINFO_LENGTH(printk_info_device, sizeof(dev_info->device));  in log_buf_vmcoreinfo_setup()
1066 static void __init log_buf_len_update(u64 size)  in log_buf_len_update()  argument
1068 	if (size > (u64)LOG_BUF_LEN_MAX) {  in log_buf_len_update()
1069 		size = (u64)LOG_BUF_LEN_MAX;  in log_buf_len_update()
1073 	if (size)  in log_buf_len_update()
1074 		size = roundup_pow_of_two(size);  in log_buf_len_update()
1075 	if (size > log_buf_len)  in log_buf_len_update()
1076 		new_log_buf_len = (unsigned long)size;  in log_buf_len_update()
1082 	u64 size;  in log_buf_len_setup()  local
1085 		return -EINVAL;  in log_buf_len_setup()
1087 	size = memparse(str, &str);  in log_buf_len_setup()
1089 	log_buf_len_update(size);  in log_buf_len_setup()
1110 	cpu_extra = (num_possible_cpus() - 1) * __LOG_CPU_MAX_BUF_LEN;  in log_buf_add_cpu()
1120 	pr_info("log_buf_len min size: %d bytes\n", __LOG_BUF_LEN);  in log_buf_add_cpu()
1139 	prb_rec_init_wr(&dest_r, r->info->text_len);  in add_to_rb()
1144 	memcpy(&dest_r.text_buf[0], &r->text_buf[0], r->info->text_len);  in add_to_rb()
1145 	dest_r.info->text_len = r->info->text_len;  in add_to_rb()
1146 	dest_r.info->facility = r->info->facility;  in add_to_rb()
1147 	dest_r.info->level = r->info->level;  in add_to_rb()
1148 	dest_r.info->flags = r->info->flags;  in add_to_rb()
1149 	dest_r.info->ts_nsec = r->info->ts_nsec;  in add_to_rb()
1150 	dest_r.info->caller_id = r->info->caller_id;  in add_to_rb()
1151 	memcpy(&dest_r.info->dev_info, &r->info->dev_info, sizeof(dest_r.info->dev_info));  in add_to_rb()
1187 	 * Some archs call setup_log_buf() multiple times - first is very  in setup_log_buf()
1188 	 * early, e.g. from setup_arch(), and second - when percpu_areas  in setup_log_buf()
1256 			free -= text_size;  in setup_log_buf()
1273 			free -= text_size;  in setup_log_buf()
1278 		       prb_next_seq(&printk_rb_static) - seq);  in setup_log_buf()
1307 		 "ignore loglevel setting (prints all kernel messages to the console)");
1351 		k--;  in boot_delay_msec()
1404 		len = print_syslog((info->facility << 3) | info->level, buf);  in info_print_prefix()
1407 		len += print_time(info->ts_nsec, buf + len);  in info_print_prefix()
1409 	len += print_caller(info->caller_id, buf + len);  in info_print_prefix()
1424  *   - Add prefix for each line.
1425  *   - Drop truncated lines that no longer fit into the buffer.
1426  *   - Add the trailing newline that has been removed in vprintk_store().
1427  *   - Add a string terminator.
1430  * return value is @r->text_buf_size - 1;
1439 	size_t text_len = r->info->text_len;  in record_print_text()
1440 	size_t buf_size = r->text_buf_size;  in record_print_text()
1441 	char *text = r->text_buf;  in record_print_text()
1456 	prefix_len = info_print_prefix(r->info, syslog, time, prefix);  in record_print_text()
1462 	 * @len:      number of bytes prepared in r->text_buf  in record_print_text()
1467 			line_len = next - text;  in record_print_text()
1484 			text_len = buf_size - len - prefix_len - 1 - 1;  in record_print_text()
1523 		text_len -= line_len + 1;  in record_print_text()
1532 		r->text_buf[len] = 0;  in record_print_text()
1551 	return ((prefix_len * line_count) + info->text_len + 1);  in get_record_print_text_size()
1556  * records up to (but not including) @max_seq fit into @size.
1559  * does not require an upper bound, -1 can be used for @max_seq.
1561 static u64 find_first_fitting_seq(u64 start_seq, u64 max_seq, size_t size,  in find_first_fitting_seq()  argument
1569 	/* Determine the size of the records up to @max_seq. */  in find_first_fitting_seq()
1590 		if (len <= size || info.seq >= max_seq)  in find_first_fitting_seq()
1592 		len -= get_record_print_text_size(&info, line_count, syslog, time);  in find_first_fitting_seq()
1598 /* The caller is responsible for making sure @size is greater than 0. */
1599 static int syslog_print(char __user *buf, int size)  in syslog_print()  argument
1609 		return -ENOMEM;  in syslog_print()
1653 		if (r.info->seq != syslog_seq) {  in syslog_print()
1655 			syslog_seq = r.info->seq;  in syslog_print()
1668 		if (n - syslog_partial <= size) {  in syslog_print()
1670 			syslog_seq = r.info->seq + 1;  in syslog_print()
1671 			n -= syslog_partial;  in syslog_print()
1675 			n = size;  in syslog_print()
1689 				len = -EFAULT;  in syslog_print()
1694 		size -= n;  in syslog_print()
1696 	} while (size);  in syslog_print()
1703 static int syslog_print_all(char __user *buf, int size, bool clear)  in syslog_print_all()  argument
1714 		return -ENOMEM;  in syslog_print_all()
1719 	 * into the user-provided buffer for this dump.  in syslog_print_all()
1721 	seq = find_first_fitting_seq(latched_seq_read_nolock(&clear_seq), -1,  in syslog_print_all()
1722 				     size, true, time);  in syslog_print_all()
1731 		if (len + textlen > size) {  in syslog_print_all()
1732 			seq--;  in syslog_print_all()
1737 			len = -EFAULT;  in syslog_print_all()
1780 			return -EINVAL;  in do_syslog()
1784 			return -EFAULT;  in do_syslog()
1794 			return -EINVAL;  in do_syslog()
1798 			return -EFAULT;  in do_syslog()
1805 	/* Disable logging to console */  in do_syslog()
1811 	/* Enable logging to console */  in do_syslog()
1818 	/* Set level of messages printed to console */  in do_syslog()
1821 			return -EINVAL;  in do_syslog()
1825 		/* Implicitly re-enable logging to console */  in do_syslog()
1843 			 * Short-cut for poll(/"proc/kmsg") which simply checks  in do_syslog()
1844 			 * for pending data, not the size; return the count of  in do_syslog()
1847 			error = prb_next_seq(prb) - syslog_seq;  in do_syslog()
1859 			error -= syslog_partial;  in do_syslog()
1863 	/* Size of the log buffer */  in do_syslog()
1868 		error = -EINVAL;  in do_syslog()
1881  * Special console_lock variants that help to reduce the risk of soft-lockups.
1896  * console_lock_spinning_enable - mark beginning of code where another
1908 	 * Non-panic CPUs abandon the flush anyway.  in console_lock_spinning_enable()
1910 	 * Just keep the lockdep annotation. The panic-CPU should avoid  in console_lock_spinning_enable()
1928  * console_lock_spinning_disable_and_check - mark end of code where another
1993  * console_trylock_spinning - try to get console_lock by busy waiting
2056 	 * The owner passed the console lock to us.  in console_trylock_spinning()
2057 	 * Since we did not spin on console lock, annotate  in console_trylock_spinning()
2074  * additional NMI context per CPU is also separately tracked. Until per-CPU
2087  * a WARN), but a higher value is used in case some printk-internal errors
2138 		(*(recursion_ptr))--;			\
2151 		while (m--) {  in printk_delay()
2165  * printk_parse_prefix - Parse level and control flags.
2195 				*level = kern_level - '0';  in printk_parse_prefix()
2210 static u16 printk_sprint(char *text, u16 size, int facility,  in printk_sprint()  argument
2216 	text_len = vscnprintf(text, size, fmt, args);  in printk_sprint()
2219 	if (text_len && text[text_len - 1] == '\n') {  in printk_sprint()
2220 		text_len--;  in printk_sprint()
2230 			text_len -= prefix_len;  in printk_sprint()
2301 			text_len = printk_sprint(&r.text_buf[r.info->text_len], reserve_size,  in vprintk_store()
2303 			r.info->text_len += text_len;  in vprintk_store()
2306 				r.info->flags |= LOG_FORCE_CON;  in vprintk_store()
2309 				r.info->flags |= LOG_NEWLINE;  in vprintk_store()
2339 	r.info->text_len = text_len + trunc_msg_len;  in vprintk_store()
2340 	r.info->facility = facility;  in vprintk_store()
2341 	r.info->level = level & 7;  in vprintk_store()
2342 	r.info->flags = flags & 0x1f;  in vprintk_store()
2343 	r.info->ts_nsec = ts_nsec;  in vprintk_store()
2344 	r.info->caller_id = caller_id;  in vprintk_store()
2346 		memcpy(&r.info->dev_info, dev_info, sizeof(r.info->dev_info));  in vprintk_store()
2361  * This acts as a one-way switch to allow legacy consoles to print from
2391 	 * non-panic CPUs are generating any messages, they will be  in vprintk_emit()
2418 		 * The caller may be holding system-critical or  in vprintk_emit()
2419 		 * timing-sensitive locks. Disable preemption during  in vprintk_emit()
2426 		 * Try to acquire and then immediately release the console  in vprintk_emit()
2464 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress);
2476 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress) { return true; }  in __pr_flush()
2481 struct console *early_console;
2496 	early_console->write(early_console, buf, n);  in early_printk()
2506 	 * @c console was defined by the user on the command line.  in set_user_specified()
2509 	c->user_specified = true;  in set_user_specified()
2510 	/* At least one console defined by the user on the command line. */  in set_user_specified()
2522 		return -EINVAL;  in __add_preferred_console()
2525 	 * We use a signed short index for struct console for device drivers to  in __add_preferred_console()
2527 	 * value is not valid when the console name and index are defined on  in __add_preferred_console()
2531 		return -EINVAL;  in __add_preferred_console()
2538 	     i < MAX_CMDLINECONSOLES && (c->name[0] || c->devname[0]);  in __add_preferred_console()
2540 		if ((name && strcmp(c->name, name) == 0 && c->index == idx) ||  in __add_preferred_console()
2541 		    (devname && strcmp(c->devname, devname) == 0)) {  in __add_preferred_console()
2549 		return -E2BIG;  in __add_preferred_console()
2553 		strscpy(c->name, name);  in __add_preferred_console()
2555 		strscpy(c->devname, devname);  in __add_preferred_console()
2556 	c->options = options;  in __add_preferred_console()
2560 	c->index = idx;  in __add_preferred_console()
2575  * Set up a console.  Called via do_early_param() in init/main.c
2576  * for each "console=" parameter in the boot command line.
2590 	 * console="" or console=null have been suggested as a way to  in console_setup()
2591 	 * disable console output. Use ttynull that has been created  in console_setup()
2602 	/* For a DEVNAME:0.0 style console the character device is unknown early */  in console_setup()
2633 		idx = -1;  in console_setup()
2642 __setup("console=", console_setup);
2645  * add_preferred_console - add a device to the list of preferred consoles.
2648  * @options: options for this console
2650  * The last preferred console added will be used for kernel messages
2652  * above to handle user-supplied console arguments; however it can also
2653  * be used by arch-specific code either to override the user or more
2654  * commonly to provide a default console (ie from PROM variables) when
2663  * match_devname_and_update_preferred_console - Update a preferred console
2666  * @name: Name of the corresponding console driver, e.g. "ttyS"
2667  * @idx: Console index, e.g. port number.
2670  * preferred via the console=DEVNAME:0.0 command line option.
2671  * It fills the missing console driver name and console index
2677  * could predict which console driver name and index this device
2690 		return -EINVAL;  in match_devname_and_update_preferred_console()
2692 	for (i = 0; i < MAX_CMDLINECONSOLES && (c->name[0] || c->devname[0]);  in match_devname_and_update_preferred_console()
2694 		if (!strcmp(devname, c->devname)) {  in match_devname_and_update_preferred_console()
2695 			pr_info("associate the preferred console \"%s\" with \"%s%d\"\n",  in match_devname_and_update_preferred_console()
2697 			strscpy(c->name, name);  in match_devname_and_update_preferred_console()
2698 			c->index = idx;  in match_devname_and_update_preferred_console()
2703 	return -ENOENT;  in match_devname_and_update_preferred_console()
2718 MODULE_PARM_DESC(console_suspend, "suspend console during suspend"
2731 MODULE_PARM_DESC(console_no_auto_verbose, "Disable console loglevel raise to highest on oops/panic/…
2734  * suspend_console - suspend the console subsystem
2740 	struct console *con;  in suspend_console()
2744 	pr_info("Suspending console(s) (use no_console_suspend to debug)\n");  in suspend_console()
2749 		console_srcu_write_flags(con, con->flags | CON_SUSPENDED);  in suspend_console()
2764 	struct console *con;  in resume_console()
2771 		console_srcu_write_flags(con, con->flags & ~CON_SUSPENDED);  in resume_console()
2791  * console_cpu_notify - print deferred console messages after CPU hotplug
2795  * will be printed on the console only if there are CON_ANYTIME consoles.
2816  * console_lock - block the console subsystem from printing
2838  * console_trylock - try to block the console subsystem from printing
2873  * Prepend the message in @pmsg->pbufs->outbuf. This is achieved by shifting
2879  * If there is not enough space in @pmsg->pbufs->outbuf, the existing
2882  * If @pmsg->pbufs->outbuf is modified, @pmsg->outbuf_len is updated.
2887 	struct printk_buffers *pbufs = pmsg->pbufs;  in console_prepend_message()
2888 	const size_t scratchbuf_sz = sizeof(pbufs->scratchbuf);  in console_prepend_message()
2889 	const size_t outbuf_sz = sizeof(pbufs->outbuf);  in console_prepend_message()
2890 	char *scratchbuf = &pbufs->scratchbuf[0];  in console_prepend_message()
2891 	char *outbuf = &pbufs->outbuf[0];  in console_prepend_message()
2908 	if (pmsg->outbuf_len + len >= outbuf_sz) {  in console_prepend_message()
2910 		pmsg->outbuf_len = outbuf_sz - (len + 1);  in console_prepend_message()
2911 		outbuf[pmsg->outbuf_len] = 0;  in console_prepend_message()
2914 	memmove(outbuf + len, outbuf, pmsg->outbuf_len + 1);  in console_prepend_message()
2916 	pmsg->outbuf_len += len;  in console_prepend_message()
2920  * Prepend the message in @pmsg->pbufs->outbuf with a "dropped message".
2921  * @pmsg->outbuf_len is updated appropriately.
2933  * Prepend the message in @pmsg->pbufs->outbuf with a "replay message".
2934  * @pmsg->outbuf_len is updated appropriately.
2947  * @pmsg will contain the formatted result. @pmsg->pbufs must point to a
2954  * console output.
2965 	struct printk_buffers *pbufs = pmsg->pbufs;  in printk_get_next_message()
2966 	const size_t scratchbuf_sz = sizeof(pbufs->scratchbuf);  in printk_get_next_message()
2967 	const size_t outbuf_sz = sizeof(pbufs->outbuf);  in printk_get_next_message()
2968 	char *scratchbuf = &pbufs->scratchbuf[0];  in printk_get_next_message()
2969 	char *outbuf = &pbufs->outbuf[0];  in printk_get_next_message()
2979 	 * Formatting normal messages is done in-place, so read the ringbuffer  in printk_get_next_message()
2990 	pmsg->seq = r.info->seq;  in printk_get_next_message()
2991 	pmsg->dropped = r.info->seq - seq;  in printk_get_next_message()
2992 	force_con = r.info->flags & LOG_FORCE_CON;  in printk_get_next_message()
2996 	 * has level above the console loglevel.  in printk_get_next_message()
2998 	if (!force_con && may_suppress && suppress_message_printing(r.info->level))  in printk_get_next_message()
3003 		len += msg_print_ext_body(outbuf + len, outbuf_sz - len,  in printk_get_next_message()
3004 					  &r.text_buf[0], r.info->text_len, &r.info->dev_info);  in printk_get_next_message()
3009 	pmsg->outbuf_len = len;  in printk_get_next_message()
3014  * Legacy console printing from printk() caller context does not respect
3020  * console write() callback when legacy printing to avoid false positive
3042  * Used as the printk buffers for non-panic, serialized console printing.
3049  * Print one record for the given console. The record printed is whatever
3050  * record is the next available record for the given console.
3058  * Returns false if the given console has no next record to print, otherwise
3063 static bool console_emit_next_record(struct console *con, bool *handover, int cookie)  in console_emit_next_record()
3074 	if (!printk_get_next_message(&pmsg, con->seq, is_extended, true))  in console_emit_next_record()
3077 	con->dropped += pmsg.dropped;  in console_emit_next_record()
3081 		con->seq = pmsg.seq + 1;  in console_emit_next_record()
3085 	if (con->dropped && !is_extended) {  in console_emit_next_record()
3086 		console_prepend_dropped(&pmsg, con->dropped);  in console_emit_next_record()
3087 		con->dropped = 0;  in console_emit_next_record()
3100 		con->write(con, outbuf, pmsg.outbuf_len);  in console_emit_next_record()
3101 		con->seq = pmsg.seq + 1;  in console_emit_next_record()
3120 		con->write(con, outbuf, pmsg.outbuf_len);  in console_emit_next_record()
3125 		con->seq = pmsg.seq + 1;  in console_emit_next_record()
3136 static bool console_emit_next_record(struct console *con, bool *handover, int cookie)  in console_emit_next_record()
3160  * Returns true when there was at least one usable console and all messages
3173 	struct console *con;  in console_flush_all()
3209 				printk_seq = con->seq;  in console_flush_all()
3252 	 * Console drivers are called with interrupts disabled, so  in __console_flush_and_unlock()
3255 	 * console registration path, and should invoke cond_resched()  in __console_flush_and_unlock()
3257 	 * scheduling stall on a slow console leading to RCU stall and  in __console_flush_and_unlock()
3282 		 * console_flush_all() but before unlocking the console.  in __console_flush_and_unlock()
3283 		 * Re-check if there is a new record to flush. If the trylock  in __console_flush_and_unlock()
3290  * console_unlock - unblock the legacy console subsystem from printing
3293  * the legacy console subsystem.
3295  * While the console_lock was held, console output may have been buffered
3314  * console_conditional_schedule - yield the CPU if required
3316  * If the console code is currently allowed to sleep, and
3332 	struct console *c;  in console_unblank()
3338 	 * console lock, which in particular can be dangerous if  in console_unblank()
3343 		if ((console_srcu_read_flags(c) & CON_ENABLED) && c->unblank) {  in console_unblank()
3353 	 * Stop console printing because the unblank() callback may  in console_unblank()
3354 	 * assume the console is not within its write() callback.  in console_unblank()
3357 	 * In that case, attempt a trylock as best-effort.  in console_unblank()
3360 		/* Semaphores are not NMI-safe. */  in console_unblank()
3365 		 * Attempting to trylock the console lock can deadlock  in console_unblank()
3380 		if ((console_srcu_read_flags(c) & CON_ENABLED) && c->unblank)  in console_unblank()
3381 			c->unblank();  in console_unblank()
3400 	struct console *c;  in __console_rewind_all()
3419 			c->seq = seq;  in __console_rewind_all()
3426  * console_flush_on_panic - flush console content on panic
3438 	 * Ignore the console lock and flush out the messages. Attempting a  in console_flush_on_panic()
3441 	 *   - if it is contended, it must be ignored anyway  in console_flush_on_panic()
3442 	 *   - console_lock() and console_trylock() block and fail  in console_flush_on_panic()
3443 	 *     respectively in panic for non-panic CPUs  in console_flush_on_panic()
3444 	 *   - semaphores are not NMI-safe  in console_flush_on_panic()
3448 	 * If another context is holding the console lock,  in console_flush_on_panic()
3467  * Return the console tty driver structure and its associated index
3471 	struct console *c;  in console_device()
3477 	 * other console operations. For example, fg_console is  in console_device()
3484 		if (!c->device)  in console_device()
3486 		driver = c->device(c, index);  in console_device()
3497  * Prevent further output on the passed console device so that (for example)
3498  * serial drivers can disable console output before suspending a port, and can
3499  * re-enable output afterwards.
3501 void console_stop(struct console *console)  in console_stop()  argument
3503 	__pr_flush(console, 1000, true);  in console_stop()
3505 	console_srcu_write_flags(console, console->flags & ~CON_ENABLED);  in console_stop()
3510 	 * be able to see that this console is disabled so that (for example)  in console_stop()
3518 void console_start(struct console *console)  in console_start()  argument
3524 	console_srcu_write_flags(console, console->flags | CON_ENABLED);  in console_start()
3525 	is_nbcon = console->flags & CON_NBCON;  in console_start()
3537 		nbcon_kthread_wake(console);  in console_start()
3541 	__pr_flush(console, 1000, true);  in console_start()
3546 static int unregister_console_locked(struct console *console);
3556 	struct console *con;  in legacy_kthread_should_wakeup()
3588 			printk_seq = con->seq;  in legacy_kthread_should_wakeup()
3631 	 * It is important that console printing threads are scheduled  in legacy_kthread_create()
3634 	sched_set_normal(printk_legacy_kthread, -20);  in legacy_kthread_create()
3640  * printk_kthreads_shutdown - shutdown all threaded printers
3648 	struct console *con;  in printk_kthreads_shutdown()
3655 			if (con->flags & CON_NBCON)  in printk_kthreads_shutdown()
3681 	struct console *con;  in printk_kthreads_check_locked()
3698 				if (con->flags & CON_NBCON)  in printk_kthreads_check_locked()
3710 	 * Printer threads cannot be started as long as any boot console is  in printk_kthreads_check_locked()
3712 	 * registers between boot console code and regular console code.  in printk_kthreads_check_locked()
3714 	 * an nbcon console is registered.  in printk_kthreads_check_locked()
3726 		if (!(con->flags & CON_NBCON))  in printk_kthreads_check_locked()
3755 	pr_info("debug: skip boot console de-registration.\n");  in keep_bootcon_setup()
3762 static int console_call_setup(struct console *newcon, char *options)  in console_call_setup()
3766 	if (!newcon->setup)  in console_call_setup()
3769 	/* Synchronize with possible boot console. */  in console_call_setup()
3771 	err = newcon->setup(newcon, options);  in console_call_setup()
3779  * the newly registered console with any of the ones selected
3786 static int try_enable_preferred_console(struct console *newcon,  in try_enable_preferred_console()
3793 	     i < MAX_CMDLINECONSOLES && (c->name[0] || c->devname[0]);  in try_enable_preferred_console()
3795 		/* Console not yet initialized? */  in try_enable_preferred_console()
3796 		if (!c->name[0])  in try_enable_preferred_console()
3798 		if (c->user_specified != user_specified)  in try_enable_preferred_console()
3800 		if (!newcon->match ||  in try_enable_preferred_console()
3801 		    newcon->match(newcon, c->name, c->index, c->options) != 0) {  in try_enable_preferred_console()
3803 			BUILD_BUG_ON(sizeof(c->name) != sizeof(newcon->name));  in try_enable_preferred_console()
3804 			if (strcmp(c->name, newcon->name) != 0)  in try_enable_preferred_console()
3806 			if (newcon->index >= 0 &&  in try_enable_preferred_console()
3807 			    newcon->index != c->index)  in try_enable_preferred_console()
3809 			if (newcon->index < 0)  in try_enable_preferred_console()
3810 				newcon->index = c->index;  in try_enable_preferred_console()
3815 			err = console_call_setup(newcon, c->options);  in try_enable_preferred_console()
3819 		newcon->flags |= CON_ENABLED;  in try_enable_preferred_console()
3821 			newcon->flags |= CON_CONSDEV;  in try_enable_preferred_console()
3827 	 * without matching. Accept the pre-enabled consoles only when match()  in try_enable_preferred_console()
3830 	if (newcon->flags & CON_ENABLED && c->user_specified ==	user_specified)  in try_enable_preferred_console()
3833 	return -ENOENT;  in try_enable_preferred_console()
3836 /* Try to enable the console unconditionally */
3837 static void try_enable_default_console(struct console *newcon)  in try_enable_default_console()
3839 	if (newcon->index < 0)  in try_enable_default_console()
3840 		newcon->index = 0;  in try_enable_default_console()
3845 	newcon->flags |= CON_ENABLED;  in try_enable_default_console()
3847 	if (newcon->device)  in try_enable_default_console()
3848 		newcon->flags |= CON_CONSDEV;  in try_enable_default_console()
3851 /* Return the starting sequence number for a newly registered console. */
3852 static u64 get_init_console_seq(struct console *newcon, bool bootcon_registered)  in get_init_console_seq()
3854 	struct console *con;  in get_init_console_seq()
3858 	if (newcon->flags & (CON_PRINTBUFFER | CON_BOOT)) {  in get_init_console_seq()
3870 		 * device as @newcon. Since it is not known which boot console  in get_init_console_seq()
3872 		 * start with the message of the enabled boot console that is  in get_init_console_seq()
3877 			 * Hold the console_lock to stop console printing and  in get_init_console_seq()
3878 			 * guarantee safe access to console->seq.  in get_init_console_seq()
3883 			 * Flush all consoles and set the console to start at  in get_init_console_seq()
3903 					if (!(con->flags & CON_BOOT) ||  in get_init_console_seq()
3904 					    !(con->flags & CON_ENABLED)) {  in get_init_console_seq()
3908 					if (con->flags & CON_NBCON)  in get_init_console_seq()
3911 						seq = con->seq;  in get_init_console_seq()
3926 	hlist_entry(console_list.first, struct console, node)
3928 static int unregister_console_locked(struct console *console);
3931  * The console driver calls this routine during kernel initialization
3932  * to register the console printing procedure with printk() and to
3934  * console driver was initialized.
3937  * early_printk) - sometimes before setup_arch() completes - be careful
3938  * of what kernel features are used - they may not be initialised yet.
3940  * There are two types of consoles - bootconsoles (early_printk) and
3943  *  - Any number of bootconsoles can be registered at any time.
3944  *  - As soon as a "real" console is registered, all bootconsoles
3946  *  - Once a "real" console is registered, any attempt to register a
3949 void register_console(struct console *newcon)  in register_console()
3951 	bool use_device_lock = (newcon->flags & CON_NBCON) && newcon->write_atomic;  in register_console()
3954 	struct console *con;  in register_console()
3962 		if (WARN(con == newcon, "console '%s%d' already registered\n",  in register_console()
3963 					 con->name, con->index)) {  in register_console()
3967 		if (con->flags & CON_BOOT)  in register_console()
3974 	if ((newcon->flags & CON_BOOT) && realcon_registered) {  in register_console()
3976 			newcon->name, newcon->index);  in register_console()
3980 	if (newcon->flags & CON_NBCON) {  in register_console()
3982 		 * Ensure the nbcon console buffers can be allocated  in register_console()
3990 	 * See if we want to enable this console driver by default.  in register_console()
3992 	 * Nope when a console is preferred by the command line, device  in register_console()
3995 	 * The first real console with tty binding (driver) wins. More  in register_console()
3998 	 * Note that a console with tty binding will have CON_CONSDEV  in register_console()
4002 		if (hlist_empty(&console_list) || !console_first()->device ||  in register_console()
4003 		    console_first()->flags & CON_BOOT) {  in register_console()
4008 	/* See if this console matches one we selected on the command line */  in register_console()
4012 	if (err == -ENOENT)  in register_console()
4015 	/* printk() messages are not printed to the Braille console. */  in register_console()
4016 	if (err || newcon->flags & CON_BRL) {  in register_console()
4017 		if (newcon->flags & CON_NBCON)  in register_console()
4023 	 * If we have a bootconsole, and are switching to a real console,  in register_console()
4024 	 * don't print everything out again, since when the boot console, and  in register_console()
4025 	 * the real console are the same physical device, it's annoying to  in register_console()
4029 	    ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {  in register_console()
4030 		newcon->flags &= ~CON_PRINTBUFFER;  in register_console()
4033 	newcon->dropped = 0;  in register_console()
4036 	if (newcon->flags & CON_NBCON) {  in register_console()
4041 		newcon->seq = init_seq;  in register_console()
4044 	if (newcon->flags & CON_BOOT)  in register_console()
4049 	 * console, it will not be aware of the nbcon synchronization. This  in register_console()
4051 	 * simultaneously if this new console is used for atomic printing  in register_console()
4055 	 * in use while this new console transitions to being registered.  in register_console()
4058 		newcon->device_lock(newcon, &flags);  in register_console()
4061 	 * Put this console in the list - keep the  in register_console()
4066 		newcon->flags |= CON_CONSDEV;  in register_console()
4067 		hlist_add_head_rcu(&newcon->node, &console_list);  in register_console()
4069 	} else if (newcon->flags & CON_CONSDEV) {  in register_console()
4071 		console_srcu_write_flags(console_first(), console_first()->flags & ~CON_CONSDEV);  in register_console()
4072 		hlist_add_head_rcu(&newcon->node, &console_list);  in register_console()
4075 		hlist_add_behind_rcu(&newcon->node, console_list.first);  in register_console()
4080 	 * on all contexts being able to see the new console before  in register_console()
4084 	/* This new console is now registered. */  in register_console()
4086 		newcon->device_unlock(newcon, flags);  in register_console()
4091 	 * By unregistering the bootconsoles after we enable the real console  in register_console()
4092 	 * we get the "console xxx enabled" message on all the consoles -  in register_console()
4093 	 * boot consoles, real consoles, etc - this is to ensure that end  in register_console()
4095 	 * went to the bootconsole (that they do not see on the real console)  in register_console()
4099 	    ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV) &&  in register_console()
4104 			if (con->flags & CON_BOOT)  in register_console()
4109 	/* Changed console list, may require printer threads to start/stop. */  in register_console()
4117 static int unregister_console_locked(struct console *console)  in unregister_console_locked()  argument
4119 	bool use_device_lock = (console->flags & CON_NBCON) && console->write_atomic;  in unregister_console_locked()
4124 	struct console *c;  in unregister_console_locked()
4129 	con_printk(KERN_INFO, console, "disabled\n");  in unregister_console_locked()
4131 	res = _braille_unregister_console(console);  in unregister_console_locked()
4137 	if (!console_is_registered_locked(console))  in unregister_console_locked()
4138 		res = -ENODEV;  in unregister_console_locked()
4139 	else if (console_is_usable(console, console->flags, true))  in unregister_console_locked()
4140 		__pr_flush(console, 1000, true);  in unregister_console_locked()
4143 	console_srcu_write_flags(console, console->flags & ~CON_ENABLED);  in unregister_console_locked()
4150 	 * in use while this console transitions to being unregistered.  in unregister_console_locked()
4153 		console->device_lock(console, &flags);  in unregister_console_locked()
4155 	hlist_del_init_rcu(&console->node);  in unregister_console_locked()
4158 		console->device_unlock(console, flags);  in unregister_console_locked()
4162 	 * If this isn't the last console and it has CON_CONSDEV set, we  in unregister_console_locked()
4163 	 * need to set it on the next preferred console.  in unregister_console_locked()
4167 	 * console has any device attached. Oh well....  in unregister_console_locked()
4169 	if (!hlist_empty(&console_list) && console->flags & CON_CONSDEV)  in unregister_console_locked()
4170 		console_srcu_write_flags(console_first(), console_first()->flags | CON_CONSDEV);  in unregister_console_locked()
4174 	 * must not be able to see this console in the list so that any  in unregister_console_locked()
4179 	if (console->flags & CON_NBCON)  in unregister_console_locked()
4180 		nbcon_free(console);  in unregister_console_locked()
4184 	if (console->exit)  in unregister_console_locked()
4185 		res = console->exit(console);  in unregister_console_locked()
4188 	 * With this console gone, the global flags tracking registered  in unregister_console_locked()
4189 	 * console types may have changed. Update them.  in unregister_console_locked()
4192 		if (c->flags & CON_BOOT)  in unregister_console_locked()
4195 		if (c->flags & CON_NBCON)  in unregister_console_locked()
4207 	/* Changed console list, may require printer threads to start/stop. */  in unregister_console_locked()
4213 int unregister_console(struct console *console)  in unregister_console()  argument
4218 	res = unregister_console_locked(console);  in unregister_console()
4225  * console_force_preferred_locked - force a registered console preferred
4226  * @con: The registered console to force preferred.
4230 void console_force_preferred_locked(struct console *con)  in console_force_preferred_locked()
4232 	struct console *cur_pref_con;  in console_force_preferred_locked()
4244 	 * Delete, but do not re-initialize the entry. This allows the console  in console_force_preferred_locked()
4246 	 * checks), even though it was briefly removed from the console list.  in console_force_preferred_locked()
4248 	hlist_del_rcu(&con->node);  in console_force_preferred_locked()
4251 	 * Ensure that all SRCU list walks have completed so that the console  in console_force_preferred_locked()
4252 	 * can be added to the beginning of the console list and its forward  in console_force_preferred_locked()
4253 	 * list pointer can be re-initialized.  in console_force_preferred_locked()
4257 	con->flags |= CON_CONSDEV;  in console_force_preferred_locked()
4258 	WARN_ON(!con->device);  in console_force_preferred_locked()
4261 	console_srcu_write_flags(cur_pref_con, cur_pref_con->flags & ~CON_CONSDEV);  in console_force_preferred_locked()
4262 	hlist_add_head_rcu(&con->node, &console_list);  in console_force_preferred_locked()
4267  * Initialize the console device. This is called *early*, so
4282 	 * set up the console device so that later boot sequences can  in console_init()
4286 	trace_initcall_level("console");  in console_init()
4302  * module, the real console hasn't registered yet at this point, there will
4303  * be a brief interval in which no messages are logged to the console, which
4308  * get unregistered when the real preferred console is registered.
4313 	struct console *con;  in printk_late_init()
4318 		if (!(con->flags & CON_BOOT))  in printk_late_init()
4323 		    init_section_contains(con->write, 0) ||  in printk_late_init()
4324 		    init_section_contains(con->read, 0) ||  in printk_late_init()
4325 		    init_section_contains(con->device, 0) ||  in printk_late_init()
4326 		    init_section_contains(con->unblank, 0) ||  in printk_late_init()
4327 		    init_section_contains(con->data, 0)) {  in printk_late_init()
4333 				con->name, con->index);  in printk_late_init()
4351 /* If @con is specified, only wait for that console. Otherwise wait for all. */
4352 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress)  in __pr_flush()
4357 	struct console *c;  in __pr_flush()
4390 		 * console->seq. Releasing console_lock flushes more  in __pr_flush()
4396 		 * console could register at any time. Always hold the  in __pr_flush()
4422 				printk_seq = c->seq;  in __pr_flush()
4426 				diff += seq - printk_seq;  in __pr_flush()
4442 		slept_jiffies = jiffies - begin_jiffies;  in __pr_flush()
4444 		remaining_jiffies -= min(slept_jiffies, remaining_jiffies);  in __pr_flush()
4453  * pr_flush() - Wait for printing threads to catch up.
4458  * A value of 0 for @timeout_ms means no waiting will occur. A value of -1
4464  * Context: Process context. May sleep while acquiring console lock.
4473  * Delayed printk version, for scheduler-internal messages:
4527  * wake_up_klogd - Wake kernel logging daemon
4530  * and the console printing of those records has already occurred or is
4542  * defer_console_output - Wake kernel logging daemon and trigger
4543  *	console printing in a deferred context
4546  * this context is responsible for console printing those records, but
4547  * the current context is not allowed to perform the console printing.
4548  * Trigger an irq_work context to perform the console printing. This
4588  * every 5s to make a denial-of-service attack impossible.
4599  * printk_timed_ratelimit - caller-controlled printk ratelimiting
4610 	unsigned long elapsed = jiffies - *caller_jiffies;  in printk_timed_ratelimit()
4624  * kmsg_dump_register - register a kernel log dumper.
4629  * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
4634 	int err = -EBUSY;  in kmsg_dump_register()
4637 	if (!dumper->dump)  in kmsg_dump_register()
4638 		return -EINVAL;  in kmsg_dump_register()
4642 	if (!dumper->registered) {  in kmsg_dump_register()
4643 		dumper->registered = 1;  in kmsg_dump_register()
4644 		list_add_tail_rcu(&dumper->list, &dump_list);  in kmsg_dump_register()
4654  * kmsg_dump_unregister - unregister a kmsg dumper.
4658  * %-EINVAL otherwise.
4663 	int err = -EINVAL;  in kmsg_dump_unregister()
4666 	if (dumper->registered) {  in kmsg_dump_unregister()
4667 		dumper->registered = 0;  in kmsg_dump_unregister()
4668 		list_del_rcu(&dumper->list);  in kmsg_dump_unregister()
4699  * kmsg_dump_desc - dump kernel log to kernel message dumpers.
4717 		enum kmsg_dump_reason max_reason = dumper->max_reason;  in kmsg_dump_desc()
4731 		dumper->dump(dumper, &detail);  in kmsg_dump_desc()
4737  * kmsg_dump_get_line - retrieve one kmsg log line
4741  * @size: maximum size of the buffer
4754 			char *line, size_t size, size_t *len)  in kmsg_dump_get_line()  argument
4763 	if (iter->cur_seq < min_seq)  in kmsg_dump_get_line()
4764 		iter->cur_seq = min_seq;  in kmsg_dump_get_line()
4766 	prb_rec_init_rd(&r, &info, line, size);  in kmsg_dump_get_line()
4770 		if (!prb_read_valid(prb, iter->cur_seq, &r))  in kmsg_dump_get_line()
4774 		if (!prb_read_valid_info(prb, iter->cur_seq,  in kmsg_dump_get_line()
4783 	iter->cur_seq = r.info->seq + 1;  in kmsg_dump_get_line()
4793  * kmsg_dump_get_buffer - copy kmsg log lines
4797  * @size: maximum size of the buffer
4812 			  char *buf, size_t size, size_t *len_out)  in kmsg_dump_get_buffer()  argument
4823 	if (!buf || !size)  in kmsg_dump_get_buffer()
4826 	if (iter->cur_seq < min_seq)  in kmsg_dump_get_buffer()
4827 		iter->cur_seq = min_seq;  in kmsg_dump_get_buffer()
4829 	if (prb_read_valid_info(prb, iter->cur_seq, &info, NULL)) {  in kmsg_dump_get_buffer()
4830 		if (info.seq != iter->cur_seq) {  in kmsg_dump_get_buffer()
4832 			iter->cur_seq = info.seq;  in kmsg_dump_get_buffer()
4837 	if (iter->cur_seq >= iter->next_seq)  in kmsg_dump_get_buffer()
4842 	 * into the user-provided buffer for this dump. Pass in size-1  in kmsg_dump_get_buffer()
4844 	 * not write more than size-1 bytes of text into @buf.  in kmsg_dump_get_buffer()
4846 	seq = find_first_fitting_seq(iter->cur_seq, iter->next_seq,  in kmsg_dump_get_buffer()
4847 				     size - 1, syslog, time);  in kmsg_dump_get_buffer()
4855 	prb_rec_init_rd(&r, &info, buf, size);  in kmsg_dump_get_buffer()
4858 		if (r.info->seq >= iter->next_seq)  in kmsg_dump_get_buffer()
4864 		prb_rec_init_rd(&r, &info, buf + len, size - len);  in kmsg_dump_get_buffer()
4867 	iter->next_seq = next_seq;  in kmsg_dump_get_buffer()
4877  * kmsg_dump_rewind - reset the iterator
4886 	iter->cur_seq = latched_seq_read_nolock(&clear_seq);  in kmsg_dump_rewind()
4887 	iter->next_seq = prb_next_seq(prb);  in kmsg_dump_rewind()
4892  * console_try_replay_all - try to replay kernel log on consoles
4894  * Try to obtain lock on console subsystem and replay all
4920 static atomic_t printk_cpu_sync_owner = ATOMIC_INIT(-1);
4929  * __printk_cpu_sync_wait() - Busy wait until the printk cpu-reentrant
4938 	} while (atomic_read(&printk_cpu_sync_owner) != -1);  in __printk_cpu_sync_wait()
4943  * __printk_cpu_sync_try_get() - Try to acquire the printk cpu-reentrant
4979 	old = atomic_cmpxchg_acquire(&printk_cpu_sync_owner, -1,  in __printk_cpu_sync_try_get()
4981 	if (old == -1) {  in __printk_cpu_sync_try_get()
4999  * __printk_cpu_sync_put() - Release the printk cpu-reentrant spinning lock.
5036 			   -1); /* LMM(__printk_cpu_sync_put:B) */  in __printk_cpu_sync_put()