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printk: add printk_delay to make messages readable for some scenarios

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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: Dave Young <hidave.darkstar@gmail.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Dave Young 2009-09-22 16:43:33 -07:00 • committed by Linus Torvalds
parent 3a3b6ed223
commit af91322ef3
4 changed files with 39 additions and 0 deletions
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15
kernel/printk.c
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@ -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 */