From af91322ef3f29ae4114e736e2a72e28b4d619cf9 Mon Sep 17 00:00:00 2001 From: Dave Young Date: Tue, 22 Sep 2009 16:43:33 -0700 Subject: 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: Dave Young Acked-by: Ingo Molnar Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/printk.c | 15 +++++++++++++++ kernel/sysctl.c | 14 ++++++++++++++ 2 files changed, 29 insertions(+) (limited to 'kernel') diff --git a/kernel/printk.c b/kernel/printk.c index 932ea21feb18..f38b07f78a4e 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -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 */ diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 6ba49c7cb128..0dfaa47d7cb6 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -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, -- cgit v1.2.3