[PATCH] Reduce stack usage in sys.c

[Yum Rayan]

Attempt to reduce stack usage in sys.c (linux-2.6.12-rc1-mm3). Stack
usage was noted using checkstack.pl. Specifically

Before patch
------------
sys_reboot - 256

After patch
-----------
sys_reboot - none (register usage only)

Along the way, wrap code to 80 column width and cleanup lock usage.

Signed-off-by: Yum Rayan <yum.rayan@xxxxxxxxx>

--- a/kernel/sys.c	2005-03-25 22:11:06.000000000 -0800
+++ b/kernel/sys.c	2005-03-30 22:34:03.000000000 -0800
@@ -369,9 +369,9 @@
  *
  * reboot doesn't sync: do that yourself before calling this.
  */
-asmlinkage long sys_reboot(int magic1, int magic2, unsigned int cmd,
void __user * arg)
+asmlinkage long sys_reboot(int magic1, int magic2,
+			   unsigned int cmd, void __user * arg)
 {
-	char buffer[256];
 
 	/* We only trust the superuser with rebooting the system. */
 	if (!capable(CAP_SYS_BOOT))
@@ -385,14 +385,15 @@
 	                magic2 != LINUX_REBOOT_MAGIC2C))
 		return -EINVAL;
 
-	lock_kernel();
 	switch (cmd) {
 	case LINUX_REBOOT_CMD_RESTART:
+		lock_kernel();
 		notifier_call_chain(&reboot_notifier_list, SYS_RESTART, NULL);
 		system_state = SYSTEM_RESTART;
 		device_shutdown();
 		printk(KERN_EMERG "Restarting system.\n");
 		machine_restart(NULL);
+		unlock_kernel();
 		break;
 
 	case LINUX_REBOOT_CMD_CAD_ON:
@@ -404,6 +405,7 @@
 		break;
 
 	case LINUX_REBOOT_CMD_HALT:
+		lock_kernel();
 		notifier_call_chain(&reboot_notifier_list, SYS_HALT, NULL);
 		system_state = SYSTEM_HALT;
 		device_shutdown();
@@ -414,6 +416,7 @@
 		break;
 
 	case LINUX_REBOOT_CMD_POWER_OFF:
+		lock_kernel();
 		notifier_call_chain(&reboot_notifier_list, SYS_POWER_OFF, NULL);
 		system_state = SYSTEM_POWER_OFF;
 		device_shutdown();
@@ -424,51 +427,60 @@
 		break;
 
 	case LINUX_REBOOT_CMD_RESTART2:
-		if (strncpy_from_user(&buffer[0], arg, sizeof(buffer) - 1) < 0) {
-			unlock_kernel();
+	{
+		char *buffer;
+		buffer = kmalloc(256, GFP_KERNEL);
+		if (!buffer)
+			return -ENOMEM;
+		if (strncpy_from_user(buffer, arg, 255) < 0) {
+			kfree(buffer);
 			return -EFAULT;
 		}
-		buffer[sizeof(buffer) - 1] = '\0';
-
+		buffer[255] = '\0';
+		lock_kernel();
 		notifier_call_chain(&reboot_notifier_list, SYS_RESTART, buffer);
 		system_state = SYSTEM_RESTART;
 		device_shutdown();
-		printk(KERN_EMERG "Restarting system with command '%s'.\n", buffer);
+		printk(KERN_EMERG "Restarting system with command '%s'.\n",
+									buffer);
 		machine_restart(buffer);
+		unlock_kernel();
+		kfree(buffer);
 		break;
-
+	}
 #ifdef CONFIG_KEXEC
 	case LINUX_REBOOT_CMD_KEXEC:
 	{
 		struct kimage *image;
 		image = xchg(&kexec_image, 0);
 		if (!image) {
-			unlock_kernel();
 			return -EINVAL;
 		}
+		lock_kernel();
 		notifier_call_chain(&reboot_notifier_list, SYS_RESTART, NULL);
 		system_state = SYSTEM_RESTART;
 		device_shutdown();
 		printk(KERN_EMERG "Starting new kernel\n");
 		machine_shutdown();
 		machine_kexec(image);
+		unlock_kernel();
 		break;
 	}
 #endif
 #ifdef CONFIG_SOFTWARE_SUSPEND
 	case LINUX_REBOOT_CMD_SW_SUSPEND:
-		{
-			int ret = software_suspend();
-			unlock_kernel();
-			return ret;
-		}
+	{
+		int ret;
+		lock_kernel();
+		ret = software_suspend();
+		unlock_kernel();
+		return ret;
+	}
 #endif
 
 	default:
-		unlock_kernel();
 		return -EINVAL;
 	}
-	unlock_kernel();
 	return 0;
 }
-
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