Commit 15ff2069 authored by Tetsuo Handa's avatar Tetsuo Handa Committed by Petr Mladek
Browse files

printk: Add caller information to printk() output. 

Sometimes we want to print a series of printk() messages to consoles
without being disturbed by concurrent printk() from interrupts and/or
other threads. But we can't enforce printk() callers to use their local
buffers because we need to ask them to make too much changes. Also, even
buffering up to one line inside printk() might cause failing to emit
an important clue under critical situation.

Therefore, instead of trying to help buffering, let's try to help
reconstructing messages by saving caller information as of calling
log_store() and adding it as "[T$thread_id]" or "[C$processor_id]"
upon printing to consoles.

Some examples for console output:

  [    1.222773][    T1] x86: Booting SMP configuration:
  [    2.779635][    T1] pci 0000:00:01.0: PCI bridge to [bus 01]
  [    5.069193][  T268] Fusion MPT base driver 3.04.20
  [    9.316504][    C2] random: fast init done
  [   13.413336][ T3355] Initialized host personality

Some examples for /dev/kmsg output:

  6,496,1222773,-,caller=T1;x86: Booting SMP configuration:
  6,968,2779635,-,caller=T1;pci 0000:00:01.0: PCI bridge to [bus 01]
   SUBSYSTEM=pci
   DEVICE=+pci:0000:00:01.0
  6,1353,5069193,-,caller=T268;Fusion MPT base driver 3.04.20
  5,1526,9316504,-,caller=C2;random: fast init done
  6,1575,13413336,-,caller=T3355;Initialized host personality

Note that this patch changes max length of messages which can be printed
by printk() or written to /dev/kmsg interface from 992 bytes to 976 bytes,
based on an assumption that userspace won't try to write messages hitting
that border line to /dev/kmsg interface.

Link: http://lkml.kernel.org/r/93f19e57-5051-c67d-9af4-b17624062d44@i-love.sakura.ne.jp


Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: LKML <linux-kernel@vger.kernel.org>
Cc: syzkaller <syzkaller@googlegroups.com>
Signed-off-by: default avatarTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: default avatarSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
parent 07c17732

kernel/printk/printk.c

+51 −4
Original line number Diff line number Diff line
@@ -357,6 +357,9 @@ struct printk_log { 
	u8 facility;		/* syslog facility */

	u8 flags:5;		/* internal record flags */

	u8 level:3;		/* syslog level */

#ifdef CONFIG_PRINTK_CALLER

	u32 caller_id;            /* thread id or processor id */

#endif

}

#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS

__packed __aligned(4)
@@ -423,7 +426,11 @@ static u64 exclusive_console_stop_seq; 
static u64 clear_seq;

static u32 clear_idx;



#ifdef CONFIG_PRINTK_CALLER

#define PREFIX_MAX		48

#else

#define PREFIX_MAX		32

#endif

#define LOG_LINE_MAX		(1024 - PREFIX_MAX)



#define LOG_LEVEL(v)		((v) & 0x07)
@@ -626,6 +633,12 @@ static int log_store(int facility, int level, 
		msg->ts_nsec = ts_nsec;

	else

		msg->ts_nsec = local_clock();

#ifdef CONFIG_PRINTK_CALLER

	if (in_task())

		msg->caller_id = task_pid_nr(current);

	else

		msg->caller_id = 0x80000000 + raw_smp_processor_id();

#endif

	memset(log_dict(msg) + dict_len, 0, pad_len);

	msg->len = size;
@@ -689,12 +702,21 @@ static ssize_t msg_print_ext_header(char *buf, size_t size, 
				    struct printk_log *msg, u64 seq)

{

	u64 ts_usec = msg->ts_nsec;

	char caller[20];

#ifdef CONFIG_PRINTK_CALLER

	u32 id = msg->caller_id;



	snprintf(caller, sizeof(caller), ",caller=%c%u",

		 id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);

#else

	caller[0] = '\0';

#endif



	do_div(ts_usec, 1000);



	return scnprintf(buf, size, "%u,%llu,%llu,%c;",

	return scnprintf(buf, size, "%u,%llu,%llu,%c%s;",

			 (msg->facility << 3) | msg->level, seq, ts_usec,

		       msg->flags & LOG_CONT ? 'c' : '-');

			 msg->flags & LOG_CONT ? 'c' : '-', caller);

}



static ssize_t msg_print_ext_body(char *buf, size_t size,
@@ -1039,6 +1061,9 @@ void log_buf_vmcoreinfo_setup(void) 
	VMCOREINFO_OFFSET(printk_log, len);

	VMCOREINFO_OFFSET(printk_log, text_len);

	VMCOREINFO_OFFSET(printk_log, dict_len);

#ifdef CONFIG_PRINTK_CALLER

	VMCOREINFO_OFFSET(printk_log, caller_id);

#endif

}

#endif
@@ -1241,6 +1266,19 @@ static size_t print_time(u64 ts, char *buf) 
		       (unsigned long)ts, rem_nsec / 1000);

}



#ifdef CONFIG_PRINTK_CALLER

static size_t print_caller(u32 id, char *buf)

{

	char caller[12];



	snprintf(caller, sizeof(caller), "%c%u",

		 id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);

	return sprintf(buf, "[%6s]", caller);

}

#else

#define print_caller(id, buf) 0

#endif



static size_t print_prefix(const struct printk_log *msg, bool syslog,

			   bool time, char *buf)

{
@@ -1248,8 +1286,17 @@ static size_t print_prefix(const struct printk_log *msg, bool syslog, 


	if (syslog)

		len = print_syslog((msg->facility << 3) | msg->level, buf);



	if (time)

		len += print_time(msg->ts_nsec, buf + len);



	len += print_caller(msg->caller_id, buf + len);



	if (IS_ENABLED(CONFIG_PRINTK_CALLER) || time) {

		buf[len++] = ' ';

		buf[len] = '\0';

	}



	return len;

}

lib/Kconfig.debug

+17 −0
Original line number Diff line number Diff line
@@ -17,6 +17,23 @@ config PRINTK_TIME 
	  The behavior is also controlled by the kernel command line

	  parameter printk.time=1. See Documentation/admin-guide/kernel-parameters.rst



config PRINTK_CALLER

	bool "Show caller information on printks"

	depends on PRINTK

	help

	  Selecting this option causes printk() to add a caller "thread id" (if

	  in task context) or a caller "processor id" (if not in task context)

	  to every message.



	  This option is intended for environments where multiple threads

	  concurrently call printk() for many times, for it is difficult to

	  interpret without knowing where these lines (or sometimes individual

	  line which was divided into multiple lines due to race) came from.



	  Since toggling after boot makes the code racy, currently there is

	  no option to enable/disable at the kernel command line parameter or

	  sysfs interface.



config CONSOLE_LOGLEVEL_DEFAULT

	int "Default console loglevel (1-15)"

	range 1 15

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