tracing: Clean up tracing_mark_write()

On gcc 4.5 the function tracing_mark_write() would give a warning
of page2 being uninitialized. This is due to a bug in gcc because
the logic prevents page2 from being used uninitialized, and
gcc 4.6+ does not complain (correctly).

Instead of adding a "unitialized" around page2, which could show
a bug later on, I combined page1 and page2 into an array map_pages[].
This binds the two and the two are modified according to nr_pages
(what gcc 4.5 seems to ignore). This no longer gives a warning with
gcc 4.5 nor with gcc 4.6.

Signed-off-by: Steven Rostedt <[email protected]>

Author: Steven Rostedt

kernel/trace/trace.c

@@ -3875,14 +3875,14 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
 	struct print_entry *entry;
 	unsigned long irq_flags;
 	struct page *pages[2];
+	void *map_page[2];
 	int nr_pages = 1;
 	ssize_t written;
-	void *page1;
-	void *page2;
 	int offset;
 	int size;
 	int len;
 	int ret;
+	int i;
 
 	if (tracing_disabled)
 		return -EINVAL;
@@ -3921,9 +3921,8 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
 		goto out;
 	}
 
-	page1 = kmap_atomic(pages[0]);
-	if (nr_pages == 2)
-		page2 = kmap_atomic(pages[1]);
+	for (i = 0; i < nr_pages; i++)
+		map_page[i] = kmap_atomic(pages[i]);
 
 	local_save_flags(irq_flags);
 	size = sizeof(*entry) + cnt + 2; /* possible \n added */
@@ -3941,10 +3940,10 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
 
 	if (nr_pages == 2) {
 		len = PAGE_SIZE - offset;
-		memcpy(&entry->buf, page1 + offset, len);
-		memcpy(&entry->buf[len], page2, cnt - len);
+		memcpy(&entry->buf, map_page[0] + offset, len);
+		memcpy(&entry->buf[len], map_page[1], cnt - len);
 	} else
-		memcpy(&entry->buf, page1 + offset, cnt);
+		memcpy(&entry->buf, map_page[0] + offset, cnt);
 
 	if (entry->buf[cnt - 1] != '\n') {
 		entry->buf[cnt] = '\n';
@@ -3959,11 +3958,10 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
 	*fpos += written;
 
  out_unlock:
-	if (nr_pages == 2)
-		kunmap_atomic(page2);
-	kunmap_atomic(page1);
-	while (nr_pages > 0)
-		put_page(pages[--nr_pages]);
+	for (i = 0; i < nr_pages; i++){
+		kunmap_atomic(map_page[i]);
+		put_page(pages[i]);
+	}
  out:
 	return written;
 }