patch-2.3.14 linux/kernel/printk.c

• Lines: 231
• Date: Mon Aug 16 23:58:59 1999
• Orig file: v2.3.13/linux/kernel/printk.c
• Orig date: Mon Aug 9 14:59:23 1999

diff -u --recursive --new-file v2.3.13/linux/kernel/printk.c linux/kernel/printk.c
@@ -46,6 +46,7 @@
 static unsigned long logged_chars = 0;
 struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 static int preferred_console = -1;
+spinlock_t console_lock = SPIN_LOCK_UNLOCKED;
 
 /*
  *	Setup a list of consoles. Called from init/main.c
@@ -117,12 +118,11 @@
  */
 int do_syslog(int type, char * buf, int len)
 {
-	unsigned long i, j, count, flags;
+	unsigned long i, j, count;
 	int do_clear = 0;
 	char c;
 	int error = -EPERM;
 
-	lock_kernel();
 	error = 0;
 	switch (type) {
 	case 0:		/* Close log */
@@ -143,18 +143,19 @@
 		if (error)
 			goto out;
 		i = 0;
+		spin_lock_irq(&console_lock);
 		while (log_size && i < len) {
 			c = *((char *) log_buf+log_start);
 			log_start++;
 			log_size--;
 			log_start &= LOG_BUF_LEN-1;
-			sti();
+			spin_unlock_irq(&console_lock);
 			__put_user(c,buf);
 			buf++;
 			i++;
-			cli();
+			spin_lock_irq(&console_lock);
 		}
-		sti();
+		spin_unlock_irq(&console_lock);
 		error = i;
 		break;
 	case 4:		/* Read/clear last kernel messages */
@@ -170,43 +171,59 @@
 		error = verify_area(VERIFY_WRITE,buf,len);
 		if (error)
 			goto out;
-		/*
-		 * The logged_chars, log_start, and log_size values may
-		 * change from an interrupt, so we disable interrupts.
-		 */
-		__save_flags(flags);
-		__cli();
 		count = len;
 		if (count > LOG_BUF_LEN)
 			count = LOG_BUF_LEN;
+		/* The logged_chars, log_start, and log_size are serialized
+		   by the console_lock (the console_lock can be acquired also
+		   from irqs by printk). */
+		spin_lock_irq(&console_lock);
 		if (count > logged_chars)
 			count = logged_chars;
 		j = log_start + log_size - count;
-		__restore_flags(flags);
+		spin_unlock_irq(&console_lock);
+		/* While writing data to the userspace buffer printk may
+		   trash our information but the _only_ thing we care is to
+		   have a coherent `j' value. */
 		for (i = 0; i < count; i++) {
 			c = *((char *) log_buf+(j++ & (LOG_BUF_LEN-1)));
 			__put_user(c, buf++);
 		}
 		if (do_clear)
+		{
+			/* the increment done in printk may undo our
+			   not atomic assigment if we do it without the
+			   console lock held. */
+			spin_lock_irq(&console_lock);
 			logged_chars = 0;
+			spin_unlock_irq(&console_lock);
+		}
 		error = i;
 		break;
 	case 5:		/* Clear ring buffer */
+		spin_lock_irq(&console_lock);
 		logged_chars = 0;
+		spin_unlock_irq(&console_lock);
 		break;
 	case 6:		/* Disable logging to console */
+		spin_lock_irq(&console_lock);
 		console_loglevel = minimum_console_loglevel;
+		spin_unlock_irq(&console_lock);
 		break;
 	case 7:		/* Enable logging to console */
+		spin_lock_irq(&console_lock);
 		console_loglevel = default_console_loglevel;
+		spin_unlock_irq(&console_lock);
 		break;
 	case 8:
 		error = -EINVAL;
 		if (len < 1 || len > 8)
 			goto out;
+		spin_lock_irq(&console_lock);
 		if (len < minimum_console_loglevel)
 			len = minimum_console_loglevel;
 		console_loglevel = len;
+		spin_unlock_irq(&console_lock);
 		error = 0;
 		break;
 	default:
@@ -214,7 +231,6 @@
 		break;
 	}
 out:
-	unlock_kernel();
 	return error;
 }
 
@@ -226,8 +242,6 @@
 }
 
 
-spinlock_t console_lock;
-
 asmlinkage int printk(const char *fmt, ...)
 {
 	va_list args;
@@ -295,21 +309,26 @@
 	struct console *c = console_drivers;
 	int len = strlen(s);
 
+	spin_lock_irq(&console_lock);
 	while(c) {
 		if ((c->flags & CON_ENABLED) && c->write)
 			c->write(c, s, len);
 		c = c->next;
 	}
+	spin_unlock_irq(&console_lock);
 }
 
 void unblank_console(void)
 {
 	struct console *c = console_drivers;
+
+	spin_lock_irq(&console_lock);
 	while(c) {
 		if ((c->flags & CON_ENABLED) && c->unblank)
 			c->unblank();
 		c = c->next;
 	}
+	spin_unlock_irq(&console_lock);
 }
 
 /*
@@ -321,11 +340,12 @@
 void register_console(struct console * console)
 {
 	int	i,j,len;
-	int	p = log_start;
+	int	p;
 	char	buf[16];
 	signed char msg_level = -1;
 	char	*q;
 
+	spin_lock_irq(&console_lock);
 	/*
 	 *	See if we want to use this console driver. If we
 	 *	didn't select a console we take the first one
@@ -364,7 +384,7 @@
 	}
 
 	if (!(console->flags & CON_ENABLED))
-		return;
+		goto out;
 
 	/*
 	 *	Put this console in the list - keep the
@@ -377,12 +397,12 @@
 		console->next = console_drivers->next;
 		console_drivers->next = console;
 	}
-	if ((console->flags & CON_PRINTBUFFER) == 0) return;
+	if ((console->flags & CON_PRINTBUFFER) == 0) goto out;
 
 	/*
 	 *	Print out buffered log messages.
 	 */
-	for (i=0,j=0; i < log_size; i++) {
+	for (p=log_start,i=0,j=0; i < log_size; i++) {
 		buf[j++] = log_buf[p];
 		p++; p &= LOG_BUF_LEN-1;
 		if (buf[j-1] != '\n' && i < log_size - 1 && j < sizeof(buf)-1)
@@ -401,26 +421,32 @@
 			msg_level = -1;
 		j = 0;
 	}
+ out:
+	spin_unlock_irq(&console_lock);
 }
 
 
 int unregister_console(struct console * console)
 {
         struct console *a,*b;
+	int ret = 0;
 	
+	spin_lock_irq(&console_lock);
 	if (console_drivers == console) {
 		console_drivers=console->next;
-		return (0);
+		goto out;
 	}
 	for (a=console_drivers->next, b=console_drivers ;
 	     a; b=a, a=b->next) {
 		if (a == console) {
 			b->next = a->next;
-			return 0;
+			goto out;
 		}  
 	}
-	
-	return (1);
+	ret = 1;
+ out:
+	spin_unlock_irq(&console_lock);
+	return ret;
 }
 	
 /*