Add support for suspending and resuming the whole console subsystem

Trying to suspend/resume with console messages flying all around is
doomed to failure, when the devices that the messages are trying to
go to are being shut down.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 27 insertions, 1 deletions

diff --git a/kernel/printk.c b/kernel/printk.c
index c056f332443..19a95561929 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -67,6 +67,7 @@ EXPORT_SYMBOL(oops_in_progress);
  * driver system.
  */
 static DECLARE_MUTEX(console_sem);
+static DECLARE_MUTEX(secondary_console_sem);
 struct console *console_drivers;
 /*
  * This is used for debugging the mess that is the VT code by
@@ -76,7 +77,7 @@ struct console *console_drivers;
  * path in the console code where we end up in places I want
  * locked without the console sempahore held
  */
-static int console_locked;
+static int console_locked, console_suspended;
 
 /*
  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
@@ -698,6 +699,23 @@ int __init add_preferred_console(char *name, int idx, char *options)
 }
 
 /**
+ * suspend_console - suspend the console subsystem
+ *
+ * This disables printk() while we go into suspend states
+ */
+void suspend_console(void)
+{
+        acquire_console_sem();
+        console_suspended = 1;
+}
+
+void resume_console(void)
+{
+        console_suspended = 0;
+        release_console_sem();
+}
+
+/**
  * acquire_console_sem - lock the console system for exclusive use.
  *
  * Acquires a semaphore which guarantees that the caller has
@@ -708,6 +726,10 @@ int __init add_preferred_console(char *name, int idx, char *options)
 void acquire_console_sem(void)
 {
         BUG_ON(in_interrupt());
+        if (console_suspended) {
+                down(&secondary_console_sem);
+                return;
+        }
         down(&console_sem);
         console_locked = 1;
         console_may_schedule = 1;
@@ -750,6 +772,10 @@ void release_console_sem(void)
         unsigned long _con_start, _log_end;
         unsigned long wake_klogd = 0;
 
+        if (console_suspended) {
+                up(&secondary_console_sem);
+                return;
+        }
         for ( ; ; ) {
                 spin_lock_irqsave(&logbuf_lock, flags);
                 wake_klogd |= log_start - log_end;