Date:	Thu, 16 Oct 2008 13:58:12 +0200 (CEST)
From:	Bodo Eggert <7eggert@....de>
To:	linux-kernel@...r.kernel.org
Subject: [PATCH] softpanic - halt booting, but allow reading why

While booting, certain panic()s have the purpose of just stopping the
machnine. This has the unfortunate side effect of preventing the user
from scrolling and looking at the cause.

This patch adds a softpanic() function, which behaves similar to panic()
in stopping the boot and possibly rebooting after a timeout, but it
does allow background activity.

Signed-off-by: Bodo Eggert <7eggert@....de>

---

I thought about merging both functions, but I don't think it would work out.

diff -pruNXdontdiff linux-2.6.27/include/linux/kernel.h linux-2.6.27.softpanic/include/linux/kernel.h
--- linux-2.6.27/include/linux/kernel.h	2008-10-10 13:18:43.000000000 +0200
+++ linux-2.6.27.softpanic/include/linux/kernel.h	2008-10-10 19:23:43.000000000 +0200
@@ -144,6 +144,12 @@ extern struct atomic_notifier_head panic
 extern long (*panic_blink)(long time);
 NORET_TYPE void panic(const char * fmt, ...)
 	__attribute__ ((NORET_AND format (printf, 1, 2))) __cold;
+#ifdef CONFIG_SOFTPANIC
+NORET_TYPE void softpanic(const char * fmt, ...)
+	__attribute__ ((NORET_AND format (printf, 1, 2))) __cold;
+#else
+# define softpanic(...) do { panic(__VA_ARGS__); } while (0)
+#endif
 extern void oops_enter(void);
 extern void oops_exit(void);
 extern int oops_may_print(void);
diff -pruNXdontdiff linux-2.6.27/init/Kconfig linux-2.6.27.softpanic/init/Kconfig
--- linux-2.6.27/init/Kconfig	2008-10-10 13:18:44.000000000 +0200
+++ linux-2.6.27.softpanic/init/Kconfig	2008-10-10 18:32:03.000000000 +0200
@@ -618,6 +618,14 @@ config BUG
           option for embedded systems with no facilities for reporting errors.
           Just say Y.
 
+config SOFTPANIC
+	bool "Enable softpanic for boot errors" if EMBEDDED
+	default y
+	help
+		Enabling this option changes a hard panic on boot errors to a
+		soft panic, which does not stop the system completely.
+		You can still scroll the screen and read the messages.
+
 config ELF_CORE
 	default y
 	bool "Enable ELF core dumps" if EMBEDDED
diff -pruNXdontdiff linux-2.6.27/init/do_mounts.c linux-2.6.27.softpanic/init/do_mounts.c
--- linux-2.6.27/init/do_mounts.c	2008-10-10 13:18:44.000000000 +0200
+++ linux-2.6.27.softpanic/init/do_mounts.c	2008-10-10 18:32:03.000000000 +0200
@@ -263,7 +263,7 @@ retry:
 		printk("Please append a correct \"root=\" boot option; here are the available partitions:\n");
 
 		printk_all_partitions();
-		panic("VFS: Unable to mount root fs on %s", b);
+		softpanic("VFS: Unable to mount root fs on %s", b);
 	}
 
 	printk("List of all partitions:\n");
@@ -275,7 +275,7 @@ retry:
 #ifdef CONFIG_BLOCK
 	__bdevname(ROOT_DEV, b);
 #endif
-	panic("VFS: Unable to mount root fs on %s", b);
+	softpanic("VFS: Unable to mount root fs on %s", b);
 out:
 	putname(fs_names);
 }
diff -pruNXdontdiff linux-2.6.27/init/main.c linux-2.6.27.softpanic/init/main.c
--- linux-2.6.27/init/main.c	2008-10-10 13:18:44.000000000 +0200
+++ linux-2.6.27.softpanic/init/main.c	2008-10-10 18:32:03.000000000 +0200
@@ -621,7 +621,7 @@ asmlinkage void __init start_kernel(void
 	 */
 	console_init();
 	if (panic_later)
-		panic(panic_later, panic_param);
+		softpanic(panic_later, panic_param);
 
 	lockdep_info();
 
@@ -830,7 +830,7 @@ static int noinline init_post(void)
 	run_init_process("/bin/init");
 	run_init_process("/bin/sh");
 
-	panic("No init found.  Try passing init= option to kernel.");
+	softpanic("No init found.  Try passing init= option to kernel.");
 }
 
 static int __init kernel_init(void * unused)
diff -pruNXdontdiff linux-2.6.27/kernel/panic.c linux-2.6.27.softpanic/kernel/panic.c
--- linux-2.6.27/kernel/panic.c	2008-10-10 13:18:45.000000000 +0200
+++ linux-2.6.27.softpanic/kernel/panic.c	2008-10-10 20:13:37.000000000 +0200
@@ -140,9 +140,68 @@ NORET_TYPE void panic(const char * fmt, 
 		i++;
 	}
 }
-
 EXPORT_SYMBOL(panic);
 
+#ifdef CONFIG_SOFTPANIC
+NORET_TYPE void softpanic(const char * fmt, ...)
+{
+	long i;
+	static char buf[1024];
+	va_list args;
+#if defined(CONFIG_S390)
+        unsigned long caller = (unsigned long) __builtin_return_address(0);
+#endif
+
+	va_start(args, fmt);
+	vsnprintf(buf, sizeof(buf), fmt, args);
+	va_end(args);
+	printk(KERN_EMERG "Kernel panic - not syncing: %s\n",buf);
+
+	atomic_notifier_call_chain(&panic_notifier_list, 0, buf);
+
+	if (!panic_blink)
+		panic_blink = no_blink;
+
+	if (panic_timeout > 0) {
+		/*
+	 	 * Delay timeout seconds before rebooting the machine. 
+		 * We can't use the "normal" timers since we just panicked..
+	 	 */
+		printk(KERN_EMERG "Rebooting in %d seconds..",panic_timeout);
+		for (i = 0; i < panic_timeout*1000; ) {
+			touch_nmi_watchdog();
+			i += panic_blink(i);
+			mdelay(1);
+			i++;
+		}
+		/*	This will not be a clean reboot, with everything
+		 *	shutting down.  But if there is a chance of
+		 *	rebooting the system it will be rebooted.
+		 */
+		kernel_restart(NULL);
+	}
+#ifdef __sparc__
+	{
+		extern int stop_a_enabled;
+		/* Make sure the user can actually press Stop-A (L1-A) */
+		stop_a_enabled = 1;
+		printk(KERN_EMERG "Press Stop-A (L1-A) to return to the boot prom\n");
+	}
+#endif
+#if defined(CONFIG_S390)
+        disabled_wait(caller);
+#endif
+	for (i = 0;;) {
+		touch_softlockup_watchdog();
+		i += panic_blink(i);
+		msleep(1);
+		i++;
+	}
+}
+EXPORT_SYMBOL(softpanic);
+#endif
+
+
 /**
  *	print_tainted - return a string to represent the kernel taint state.
  *

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