From 7bf693951a8e5f7e600a45b74d91d962a453146e Mon Sep 17 00:00:00 2001 From: "Fabio M. Di Nitto" Date: Tue, 22 Mar 2011 16:34:20 -0700 Subject: console: allow to retain boot console via boot option keep_bootcon On some architectures, the boot process involves de-registering the boot console (early boot), initialize drivers and then re-register the console. This mechanism introduces a window in which no printk can happen on the console and messages are buffered and then printed once the new console is available. If a kernel crashes during this window, all it's left on the boot console is "console [foo] enabled, bootconsole disabled" making debug of the crash rather 'interesting'. By adding "keep_bootcon" option, do not unregister the boot console, that will allow to printk everything that is happening up to the crash. The option is clearly meant only for debugging purposes as it introduces lots of duplicated info printed on console, but will make bug report from users easier as it doesn't require a kernel build just to figure out where we crash. Signed-off-by: Fabio M. Di Nitto Acked-by: David S. Miller Cc: Alan Cox Cc: Greg KH Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/printk.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) (limited to 'kernel/printk.c') diff --git a/kernel/printk.c b/kernel/printk.c index 33284adb218..2b591f252e5 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -1316,6 +1316,18 @@ void console_start(struct console *console) } EXPORT_SYMBOL(console_start); +static int __read_mostly keep_bootcon; + +static int __init keep_bootcon_setup(char *str) +{ + keep_bootcon = 1; + printk(KERN_INFO "debug: skip boot console de-registration.\n"); + + return 0; +} + +early_param("keep_bootcon", keep_bootcon_setup); + /* * The console driver calls this routine during kernel initialization * to register the console printing procedure with printk() and to @@ -1463,7 +1475,9 @@ void register_console(struct console *newcon) * users know there might be something in the kernel's log buffer that * went to the bootconsole (that they do not see on the real console) */ - if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) { + if (bcon && + ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV) && + !keep_bootcon) { /* we need to iterate through twice, to make sure we print * everything out, before we unregister the console(s) */ -- cgit v1.2.3-70-g09d2 From fe3d8ad31cf51b062bbb8a9609eeb1d0c41a7f30 Mon Sep 17 00:00:00 2001 From: Feng Tang Date: Tue, 22 Mar 2011 16:34:21 -0700 Subject: console: prevent registered consoles from dumping old kernel message over again For a platform with many consoles like: "console=tty1 console=ttyMFD2 console=ttyS0 earlyprintk=mrst" Each time when the non "selected_console" (tty1 and ttyMFD2 here) get registered, the existing kernel message will be printed out on registered consoles again, the "mrst" early console will get some same message for 3 times, and "tty1" will get some for twice. As suggested by Andrew Morton, every time a new console is registered, it will be set as the "exclusive" console which will dump the already existing kernel messages. Signed-off-by: Feng Tang Cc: Greg KH Cc: Alan Cox Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/printk.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) (limited to 'kernel/printk.c') diff --git a/kernel/printk.c b/kernel/printk.c index 2b591f252e5..a53607eea6d 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -112,6 +112,11 @@ static unsigned log_start; /* Index into log_buf: next char to be read by syslog static unsigned con_start; /* Index into log_buf: next char to be sent to consoles */ static unsigned log_end; /* Index into log_buf: most-recently-written-char + 1 */ +/* + * If exclusive_console is non-NULL then only this console is to be printed to. + */ +static struct console *exclusive_console; + /* * Array of consoles built from command line options (console=) */ @@ -476,6 +481,8 @@ static void __call_console_drivers(unsigned start, unsigned end) struct console *con; for_each_console(con) { + if (exclusive_console && con != exclusive_console) + continue; if ((con->flags & CON_ENABLED) && con->write && (cpu_online(smp_processor_id()) || (con->flags & CON_ANYTIME))) @@ -1230,6 +1237,11 @@ void console_unlock(void) local_irq_restore(flags); } console_locked = 0; + + /* Release the exclusive_console once it is used */ + if (unlikely(exclusive_console)) + exclusive_console = NULL; + up(&console_sem); spin_unlock_irqrestore(&logbuf_lock, flags); if (wake_klogd) @@ -1464,6 +1476,12 @@ void register_console(struct console *newcon) spin_lock_irqsave(&logbuf_lock, flags); con_start = log_start; spin_unlock_irqrestore(&logbuf_lock, flags); + /* + * We're about to replay the log buffer. Only do this to the + * just-registered console to avoid excessive message spam to + * the already-registered consoles. + */ + exclusive_console = newcon; } console_unlock(); console_sysfs_notify(); -- cgit v1.2.3-70-g09d2 From 5af5bcb8d37f99ba415a1adc6da71051b84f93a5 Mon Sep 17 00:00:00 2001 From: Mandeep Singh Baines Date: Tue, 22 Mar 2011 16:34:23 -0700 Subject: printk: allow setting DEFAULT_MESSAGE_LEVEL via Kconfig We've been burned by regressions/bugs which we later realized could have been triaged quicker if only we'd paid closer attention to dmesg. To make it easier to audit dmesg, we'd like to make DEFAULT_MESSAGE_LEVEL Kconfig-settable. That way we can set it to KERN_NOTICE and audit any messages <= KERN_WARNING. Signed-off-by: Mandeep Singh Baines Cc: Ingo Molnar Cc: Joe Perches Cc: Olof Johansson Cc: Randy Dunlap Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/printk.c | 2 +- lib/Kconfig.debug | 11 +++++++++++ 2 files changed, 12 insertions(+), 1 deletion(-) (limited to 'kernel/printk.c') diff --git a/kernel/printk.c b/kernel/printk.c index a53607eea6d..da8ca817eae 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -53,7 +53,7 @@ void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...) #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT) /* printk's without a loglevel use this.. */ -#define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */ +#define DEFAULT_MESSAGE_LOGLEVEL CONFIG_DEFAULT_MESSAGE_LOGLEVEL /* We show everything that is MORE important than this.. */ #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */ diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index fb0afeff943..bef5faab660 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -9,6 +9,17 @@ config PRINTK_TIME operations. This is useful for identifying long delays in kernel startup. +config DEFAULT_MESSAGE_LOGLEVEL + int "Default message log level (1-7)" + range 1 7 + default "4" + help + Default log level for printk statements with no specified priority. + + This was hard-coded to KERN_WARNING since at least 2.6.10 but folks + that are auditing their logs closely may want to set it to a lower + priority. + config ENABLE_WARN_DEPRECATED bool "Enable __deprecated logic" default y -- cgit v1.2.3-70-g09d2