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 <rostedt@goodmis.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 48ef496..d1b3469 100644 (file)
--- a/kernel/trace/trace.c
+++ b/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;
 }