printk simultaneous oops disentangling

@@ -390,6 +390,9 @@
 		logged_chars++;
 }
 
+/* cpu currently holding logbuf_lock */
+static volatile int printk_cpu = -1;
+
 /*
  * This is printk.  It can be called from any context.  We want it to work.
  * 

@@ -412,8 +415,9 @@
 	static char printk_buf[1024];
 	static int log_level_unknown = 1;
 
-	if (oops_in_progress) {
-		/* If a crash is occurring, make sure we can't deadlock */
+	if (oops_in_progress && printk_cpu==smp_processor_id()) {
+		/* If a crash is occurring during printk() on this CPU,
+		 * make sure we can't deadlock */
 		spin_lock_init(&logbuf_lock);
 		/* And make sure that we print immediately */
 		init_MUTEX(&console_sem);

@@ -421,6 +425,7 @@
 
 	/* This stops the holder of console_sem just where we want him */
 	spin_lock_irqsave(&logbuf_lock, flags);
+	printk_cpu = smp_processor_id();
 
 	/* Emit the output into the temporary buffer */
 	va_start(args, fmt);

@@ -450,6 +455,7 @@
 		 * On some architectures, the consoles are not usable
 		 * on secondary CPUs early in the boot process.
 		 */
+		printk_cpu = -1;
 		spin_unlock_irqrestore(&logbuf_lock, flags);
 		goto out;
 	}

@@ -458,6 +464,7 @@
 		 * We own the drivers.  We can drop the spinlock and let
 		 * release_console_sem() print the text
 		 */
+		printk_cpu = -1;
 		spin_unlock_irqrestore(&logbuf_lock, flags);
 		console_may_schedule = 0;
 		release_console_sem();

@@ -467,6 +474,7 @@
 		 * allows the semaphore holder to proceed and to call the
 		 * console drivers with the output which we just produced.
 		 */
+		printk_cpu = -1;
 		spin_unlock_irqrestore(&logbuf_lock, flags);
 	}
 out: