[PATCH v4] panic/reboot: allow specifying reboot_mode for panic only

[Aaro Koskinen]

From: Aaro Koskinen <aaro.koskinen@xxxxxxxxx>

Allow specifying reboot_mode for panic only. This is needed on systems
where ramoops is used to store panic logs, and user wants to use warm
reset to preserve those, while still having cold reset on normal reboots.

Signed-off-by: Aaro Koskinen <aaro.koskinen@xxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
---

	v4: Add Reviewed-by tag.

	v3: https://marc.info/?t=155079054500003&r=1&w=2
	    Move REBOOT_UNDEFINED before REBOOT_COLD.                         

	v2: https://marc.info/?t=155078129700004&r=1&w=2                      
	    Use REBOOT_UNDEFINED instead of -1                                

	v1: https://marc.info/?t=154957416600005&r=1&w=2                      

 .../admin-guide/kernel-parameters.txt         |  4 +++-
 include/linux/reboot.h                        |  2 ++
 kernel/panic.c                                |  2 ++
 kernel/reboot.c                               | 20 ++++++++++++++-----
 4 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 2b8ee90bb644..b470f44ee02a 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3986,7 +3986,9 @@
 				[[,]s[mp]#### \
 				[[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
 				[[,]f[orce]
-			Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
+			Where reboot_mode is one of warm (soft) or cold (hard) or gpio
+					(prefix with 'panic_' to set mode for panic
+					reboot only),
 			      reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
 			      reboot_force is either force or not specified,
 			      reboot_cpu is s[mp]#### with #### being the processor
diff --git a/include/linux/reboot.h b/include/linux/reboot.h
index e63799a6e895..3734cd8f38a8 100644
--- a/include/linux/reboot.h
+++ b/include/linux/reboot.h
@@ -14,6 +14,7 @@ struct device;
 #define SYS_POWER_OFF	0x0003	/* Notify of system power off */
 
 enum reboot_mode {
+	REBOOT_UNDEFINED = -1,
 	REBOOT_COLD = 0,
 	REBOOT_WARM,
 	REBOOT_HARD,
@@ -21,6 +22,7 @@ enum reboot_mode {
 	REBOOT_GPIO,
 };
 extern enum reboot_mode reboot_mode;
+extern enum reboot_mode panic_reboot_mode;
 
 enum reboot_type {
 	BOOT_TRIPLE	= 't',
diff --git a/kernel/panic.c b/kernel/panic.c
index 0ae0d7332f12..aad890082f13 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -306,6 +306,8 @@ void panic(const char *fmt, ...)
 		 * shutting down.  But if there is a chance of
 		 * rebooting the system it will be rebooted.
 		 */
+		if (panic_reboot_mode != REBOOT_UNDEFINED)
+			reboot_mode = panic_reboot_mode;
 		emergency_restart();
 	}
 #ifdef __sparc__
diff --git a/kernel/reboot.c b/kernel/reboot.c
index e1b79b6a2735..b9e79e8c7226 100644
--- a/kernel/reboot.c
+++ b/kernel/reboot.c
@@ -31,6 +31,7 @@ EXPORT_SYMBOL(cad_pid);
 #define DEFAULT_REBOOT_MODE
 #endif
 enum reboot_mode reboot_mode DEFAULT_REBOOT_MODE;
+enum reboot_mode panic_reboot_mode = REBOOT_UNDEFINED;
 
 /*
  * This variable is used privately to keep track of whether or not
@@ -519,6 +520,8 @@ EXPORT_SYMBOL_GPL(orderly_reboot);
 static int __init reboot_setup(char *str)
 {
 	for (;;) {
+		enum reboot_mode *mode;
+
 		/*
 		 * Having anything passed on the command line via
 		 * reboot= will cause us to disable DMI checking
@@ -526,17 +529,24 @@ static int __init reboot_setup(char *str)
 		 */
 		reboot_default = 0;
 
+		if (!strncmp(str, "panic_", 6)) {
+			mode = &panic_reboot_mode;
+			str += 6;
+		} else {
+			mode = &reboot_mode;
+		}
+
 		switch (*str) {
 		case 'w':
-			reboot_mode = REBOOT_WARM;
+			*mode = REBOOT_WARM;
 			break;
 
 		case 'c':
-			reboot_mode = REBOOT_COLD;
+			*mode = REBOOT_COLD;
 			break;
 
 		case 'h':
-			reboot_mode = REBOOT_HARD;
+			*mode = REBOOT_HARD;
 			break;
 
 		case 's':
@@ -553,11 +563,11 @@ static int __init reboot_setup(char *str)
 				if (rc)
 					return rc;
 			} else
-				reboot_mode = REBOOT_SOFT;
+				*mode = REBOOT_SOFT;
 			break;
 		}
 		case 'g':
-			reboot_mode = REBOOT_GPIO;
+			*mode = REBOOT_GPIO;
 			break;
 
 		case 'b':
-- 
2.17.0