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authorMichael Ellerman <michael@ellerman.id.au>2006-06-25 05:47:40 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-06-25 10:01:05 -0700
commit76a8ad293912cd2f01eca075d80cd0ddec30c627 (patch)
tree1ff683dcd5b1351b403d3efe701d0dd9eddcd773
parent8ae6e163c1b637e1cb125613726ffbd31ca44fdf (diff)
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[PATCH] Make printk work for really early debugging
Currently printk is no use for early debugging because it refuses to actually print anything to the console unless cpu_online(smp_processor_id()) is true. The stated explanation is that console drivers may require per-cpu resources, or otherwise barf, because the system is not yet setup correctly. Fair enough. However some console drivers might be quite happy running early during boot, in fact we have one, and so it'd be nice if printk understood that. So I added a flag (which I would have called CON_BOOT, but that's taken) called CON_ANYTIME, which indicates that a console is happy to be called anytime, even if the cpu is not yet online. Tested on a Power 5 machine, with both a CON_ANYTIME driver and a bogus console driver that BUG()s if called while offline. No problems AFAICT. Built for i386 UP & SMP. Signed-off-by: Michael Ellerman <michael@ellerman.id.au> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
-rw-r--r--include/linux/console.h1
-rw-r--r--kernel/printk.c50
2 files changed, 34 insertions, 17 deletions
diff --git a/include/linux/console.h b/include/linux/console.h
index 08734e660d41..d0f8a8009490 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -87,6 +87,7 @@ void give_up_console(const struct consw *sw);
#define CON_CONSDEV (2) /* Last on the command line */
#define CON_ENABLED (4)
#define CON_BOOT (8)
+#define CON_ANYTIME (16) /* Safe to call when cpu is offline */
struct console
{
diff --git a/kernel/printk.c b/kernel/printk.c
index 19a955619294..6b89dd9d11b6 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -327,7 +327,9 @@ static void __call_console_drivers(unsigned long start, unsigned long end)
struct console *con;
for (con = console_drivers; con; con = con->next) {
- if ((con->flags & CON_ENABLED) && con->write)
+ if ((con->flags & CON_ENABLED) && con->write &&
+ (cpu_online(smp_processor_id()) ||
+ (con->flags & CON_ANYTIME)))
con->write(con, &LOG_BUF(start), end - start);
}
}
@@ -453,6 +455,18 @@ __attribute__((weak)) unsigned long long printk_clock(void)
return sched_clock();
}
+/* Check if we have any console registered that can be called early in boot. */
+static int have_callable_console(void)
+{
+ struct console *con;
+
+ for (con = console_drivers; con; con = con->next)
+ if (con->flags & CON_ANYTIME)
+ return 1;
+
+ return 0;
+}
+
/**
* printk - print a kernel message
* @fmt: format string
@@ -566,27 +580,29 @@ asmlinkage int vprintk(const char *fmt, va_list args)
log_level_unknown = 1;
}
- if (!cpu_online(smp_processor_id())) {
+ if (!down_trylock(&console_sem)) {
/*
- * Some console drivers may assume that per-cpu resources have
- * been allocated. So don't allow them to be called by this
- * CPU until it is officially up. We shouldn't be calling into
- * random console drivers on a CPU which doesn't exist yet..
+ * We own the drivers. We can drop the spinlock and
+ * let release_console_sem() print the text, maybe ...
*/
+ console_locked = 1;
printk_cpu = UINT_MAX;
spin_unlock_irqrestore(&logbuf_lock, flags);
- goto out;
- }
- if (!down_trylock(&console_sem)) {
- console_locked = 1;
+
/*
- * We own the drivers. We can drop the spinlock and let
- * release_console_sem() print the text
+ * Console drivers may assume that per-cpu resources have
+ * been allocated. So unless they're explicitly marked as
+ * being able to cope (CON_ANYTIME) don't call them until
+ * this CPU is officially up.
*/
- printk_cpu = UINT_MAX;
- spin_unlock_irqrestore(&logbuf_lock, flags);
- console_may_schedule = 0;
- release_console_sem();
+ if (cpu_online(smp_processor_id()) || have_callable_console()) {
+ console_may_schedule = 0;
+ release_console_sem();
+ } else {
+ /* Release by hand to avoid flushing the buffer. */
+ console_locked = 0;
+ up(&console_sem);
+ }
} else {
/*
* Someone else owns the drivers. We drop the spinlock, which
@@ -596,7 +612,7 @@ asmlinkage int vprintk(const char *fmt, va_list args)
printk_cpu = UINT_MAX;
spin_unlock_irqrestore(&logbuf_lock, flags);
}
-out:
+
preempt_enable();
return printed_len;
}