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

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
......@@ -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
......
......@@ -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):
*/
......
......@@ -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 */
......
......@@ -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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