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| # cat /proc/sys/kernel/printk
15 4 1 7
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在正常的printk日志输出级别中只有0～7，为何会出现15？
原因是内核lock的状态检测到异常后，在进行相关锁状态信息输出前，将console的level配置成15
printk级别
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| int console_printk[4] = {
CONSOLE_LOGLEVEL_DEFAULT, /* console_loglevel */
MESSAGE_LOGLEVEL_DEFAULT, /* default_message_loglevel */
CONSOLE_LOGLEVEL_MIN, /* minimum_console_loglevel */
CONSOLE_LOGLEVEL_DEFAULT, /* default_console_loglevel */
};
EXPORT_SYMBOL_GPL(console_printk);
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kernel/printk/printk.c
出现异常时调整的是console_loglevel，其默认值为:
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| #define CONSOLE_LOGLEVEL_DEFAULT CONFIG_CONSOLE_LOGLEVEL_DEFAULT
CONFIG_CONSOLE_LOGLEVEL_DEFAULT=7 //内核配置
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kernel日志等级：
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| /* integer equivalents of KERN_<LEVEL> */
#define LOGLEVEL_SCHED -2 /* Deferred messages from sched code
* are set to this special level */
#define LOGLEVEL_DEFAULT -1 /* default (or last) loglevel */
#define LOGLEVEL_EMERG 0 /* system is unusable */
#define LOGLEVEL_ALERT 1 /* action must be taken immediately */
#define LOGLEVEL_CRIT 2 /* critical conditions */
#define LOGLEVEL_ERR 3 /* error conditions */
#define LOGLEVEL_WARNING 4 /* warning conditions */
#define LOGLEVEL_NOTICE 5 /* normal but significant condition */
#define LOGLEVEL_INFO 6 /* informational */
#define LOGLEVEL_DEBUG 7 /* debug-level messages */
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include/linux/kern_levels.h
console_loglevel
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| #define console_loglevel (console_printk[0])
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调整接口：
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| #define CONSOLE_LOGLEVEL_MOTORMOUTH 15 /* You can't shut this one up */
static inline void console_verbose(void)
{
if (console_loglevel)
console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH;
}
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include/linux/printk.h
也就是通过console_verbose接口，将console等级调整为15.
console_verbose的调用流程
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| print_unlock_imbalance_bug
\-> debug_locks_off
\-> console_verbose //打开console全部输出，级别15 lib/debug_locks.c
\-> dump_stack
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