[PATCH] PPC64 rtasd: window when error_log_cnt could get zeroed

This patch is from Jake Moilanen <moilanen@austin.ibm.com>.

There appears to be a hole that if we get an log_error() call, that we could
zero out our error log count in nvram. 

When rtasd() starts up, it turns on the logging via 'no_more_logging = 0'.  If
we get a log_error() call after that is set but before nvram_read_error_log
has actually read nvram to set error_log_cnt, the log_error() call will write
back to nvram a uninitialized error_log_cnt value, and wipe out our sequence
number.

To close the hole, simply move the 'no_more_logging = 0' till after nvram sets
error_log_cnt but before pSeries_log_error is called.

I also changed the 'no_more_logging' variable to be 'no_logging' since it's
not only used when we stop logging now.  I also removed the "volatile" part of
no_more_logging, since it's unneeded.  
Signed-off-by: Jake Moilanen <moilanen@austin.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/ppc64/kernel/nvram.c

@@ -43,9 +43,9 @@ static struct nvram_partition * nvram_part;
 static long nvram_error_log_index = -1;
 static long nvram_error_log_size = 0;
 
-volatile int no_more_logging = 1; /* Until we initialize everything,
-				   * make sure we don't try logging
-				   * anything */
+int no_logging = 1; 	/* Until we initialize everything,
+			 * make sure we don't try logging
+			 * anything */
 
 extern volatile int error_log_cnt;
 
@@ -640,7 +640,7 @@ int nvram_write_error_log(char * buff, int length, unsigned int err_type)
 	loff_t tmp_index;
 	struct err_log_info info;
 	
-	if (no_more_logging) {
+	if (no_logging) {
 		return -EPERM;
 	}
 

arch/ppc64/kernel/rtasd.c

@@ -48,7 +48,7 @@ static unsigned int rtas_error_log_buffer_max;
 
 static int full_rtas_msgs = 0;
 
-extern volatile int no_more_logging;
+extern int no_logging;
 
 volatile int error_log_cnt = 0;
 
@@ -213,7 +213,7 @@ void pSeries_log_error(char *buf, unsigned int err_type, int fatal)
 	}
 
 	/* Write error to NVRAM */
-	if (!no_more_logging && !(err_type & ERR_FLAG_BOOT))
+	if (!no_logging && !(err_type & ERR_FLAG_BOOT))
 		nvram_write_error_log(buf, len, err_type);
 
 	/*
@@ -225,8 +225,8 @@ void pSeries_log_error(char *buf, unsigned int err_type, int fatal)
 		printk_log_rtas(buf, len);
 
 	/* Check to see if we need to or have stopped logging */
-	if (fatal || no_more_logging) {
-		no_more_logging = 1;
+	if (fatal || no_logging) {
+		no_logging = 1;
 		spin_unlock_irqrestore(&rtasd_log_lock, s);
 		return;
 	}
@@ -299,7 +299,7 @@ static ssize_t rtas_log_read(struct file * file, char __user * buf,
 
 	spin_lock_irqsave(&rtasd_log_lock, s);
 	/* if it's 0, then we know we got the last one (the one in NVRAM) */
-	if (rtas_log_size == 0 && !no_more_logging)
+	if (rtas_log_size == 0 && !no_logging)
 		nvram_clear_error_log();
 	spin_unlock_irqrestore(&rtasd_log_lock, s);
 
@@ -417,9 +417,6 @@ static int rtasd(void *unused)
 		goto error;
 	}
 
-	/* We can use rtas_log_buf now */
-	no_more_logging = 0;
-
 	printk(KERN_ERR "RTAS daemon started\n");
 
 	DEBUG("will sleep for %d jiffies\n", (HZ*60/rtas_event_scan_rate) / 2);
@@ -428,6 +425,10 @@ static int rtasd(void *unused)
 	memset(logdata, 0, rtas_error_log_max);
 
 	rc = nvram_read_error_log(logdata, rtas_error_log_max, &err_type);
+
+	/* We can use rtas_log_buf now */
+	no_logging = 0;
+
 	if (!rc) {
 		if (err_type != ERR_FLAG_ALREADY_LOGGED) {
 			pSeries_log_error(logdata, err_type | ERR_FLAG_BOOT, 0);