Commit af91322e authored by Dave Young's avatar Dave Young Committed by Linus Torvalds
Browse files

printk: add printk_delay to make messages readable for some scenarios 



When syslog is not possible, at the same time there's no serial/net
console available, it will be hard to read the printk messages.  For
example oops/panic/warning messages in shutdown phase.

Add a printk delay feature, we can make each printk message delay some
milliseconds.

Setting the delay by proc/sysctl interface: /proc/sys/kernel/printk_delay

The value range from 0 - 10000, default value is 0

[akpm@linux-foundation.org: fix a few things]
Signed-off-by: default avatarDave Young <hidave.darkstar@gmail.com>
Acked-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3a3b6ed2

Documentation/sysctl/kernel.txt

+8 −0
Original line number Diff line number Diff line
@@ -313,6 +313,14 @@ send before ratelimiting kicks in. 


==============================================================



printk_delay:



Delay each printk message in printk_delay milliseconds



Value from 0 - 10000 is allowed.



==============================================================



randomize-va-space:



This option can be used to select the type of process address

include/linux/kernel.h

+2 −0
Original line number Diff line number Diff line
@@ -246,6 +246,8 @@ extern int printk_ratelimit(void); 
extern bool printk_timed_ratelimit(unsigned long *caller_jiffies,

				   unsigned int interval_msec);



extern int printk_delay_msec;



/*

 * Print a one-time message (analogous to WARN_ONCE() et al):

 */

kernel/printk.c

+15 −0
Original line number Diff line number Diff line
@@ -653,6 +653,20 @@ static int recursion_bug; 
static int new_text_line = 1;

static char printk_buf[1024];



int printk_delay_msec __read_mostly;



static inline void printk_delay(void)

{

	if (unlikely(printk_delay_msec)) {

		int m = printk_delay_msec;



		while (m--) {

			mdelay(1);

			touch_nmi_watchdog();

		}

	}

}



asmlinkage int vprintk(const char *fmt, va_list args)

{

	int printed_len = 0;
@@ -662,6 +676,7 @@ asmlinkage int vprintk(const char *fmt, va_list args) 
	char *p;



	boot_delay_msec();

	printk_delay();



	preempt_disable();

	/* This stops the holder of console_sem just where we want him */

kernel/sysctl.c

+14 −0
Original line number Diff line number Diff line
@@ -106,6 +106,9 @@ static int __maybe_unused one = 1; 
static int __maybe_unused two = 2;

static unsigned long one_ul = 1;

static int one_hundred = 100;

#ifdef CONFIG_PRINTK

static int ten_thousand = 10000;

#endif



/* this is needed for the proc_doulongvec_minmax of vm_dirty_bytes */

static unsigned long dirty_bytes_min = 2 * PAGE_SIZE;
@@ -722,6 +725,17 @@ static struct ctl_table kern_table[] = { 
		.mode		= 0644,

		.proc_handler	= &proc_dointvec,

	},

	{

		.ctl_name	= CTL_UNNUMBERED,

		.procname	= "printk_delay",

		.data		= &printk_delay_msec,

		.maxlen		= sizeof(int),

		.mode		= 0644,

		.proc_handler	= &proc_dointvec_minmax,

		.strategy	= &sysctl_intvec,

		.extra1		= &zero,

		.extra2		= &ten_thousand,

	},

#endif

	{

		.ctl_name	= KERN_NGROUPS_MAX,

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