ftrace: add debugfs entry 'failures'

Identify functions which had their mcount call-site updates failed. This can
help us track functions which ftrace shouldn't fiddle with, and are thus not
being traced. If there is no race with any external agent which is modifying
the mcount call-site, then this file displays no entries (normal case).

Signed-off-by: Abhishek Sagar <sagar.abhishek@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index a8929e4c77c1b6aed45e463ba639d40c22937151..ad568c742bfc7e5c6e6a6c89644c33d5b8900d66 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -768,6 +768,7 @@ enum {
        FTRACE_ITER_FILTER      = (1 << 0),
        FTRACE_ITER_CONT        = (1 << 1),
        FTRACE_ITER_NOTRACE     = (1 << 2),
+       FTRACE_ITER_FAILURES    = (1 << 3),
 };
 
 #define FTRACE_BUFF_MAX (KSYM_SYMBOL_LEN+4) /* room for wildcards */
@@ -799,9 +800,16 @@ t_next(struct seq_file *m, void *v, loff_t *pos)
                }
        } else {
                rec = &iter->pg->records[iter->idx++];
-               if ((rec->flags & FTRACE_FL_FAILED) ||
+               if ((!(iter->flags & FTRACE_ITER_FAILURES) &&
+                    (rec->flags & FTRACE_FL_FAILED)) ||
+
+                   ((iter->flags & FTRACE_ITER_FAILURES) &&
+                    (!(rec->flags & FTRACE_FL_FAILED) ||
+                     (rec->flags & FTRACE_FL_FREE))) ||
+
                    ((iter->flags & FTRACE_ITER_FILTER) &&
                     !(rec->flags & FTRACE_FL_FILTER)) ||
+
                    ((iter->flags & FTRACE_ITER_NOTRACE) &&
                     !(rec->flags & FTRACE_FL_NOTRACE))) {
                        rec = NULL;
@@ -896,6 +904,24 @@ int ftrace_avail_release(struct inode *inode, struct file *file)
        return 0;
 }
 
+static int
+ftrace_failures_open(struct inode *inode, struct file *file)
+{
+       int ret;
+       struct seq_file *m;
+       struct ftrace_iterator *iter;
+
+       ret = ftrace_avail_open(inode, file);
+       if (!ret) {
+               m = (struct seq_file *)file->private_data;
+               iter = (struct ftrace_iterator *)m->private;
+               iter->flags = FTRACE_ITER_FAILURES;
+       }
+
+       return ret;
+}
+
+
 static void ftrace_filter_reset(int enable)
 {
        struct ftrace_page *pg;
@@ -1309,6 +1335,13 @@ static struct file_operations ftrace_avail_fops = {
        .release = ftrace_avail_release,
 };
 
+static struct file_operations ftrace_failures_fops = {
+       .open = ftrace_failures_open,
+       .read = seq_read,
+       .llseek = seq_lseek,
+       .release = ftrace_avail_release,
+};
+
 static struct file_operations ftrace_filter_fops = {
        .open = ftrace_filter_open,
        .read = ftrace_regex_read,
@@ -1386,6 +1419,11 @@ static __init int ftrace_init_debugfs(void)
                pr_warning("Could not create debugfs "
                           "'available_filter_functions' entry\n");
 
+       entry = debugfs_create_file("failures", 0444,
+                                   d_tracer, NULL, &ftrace_failures_fops);
+       if (!entry)
+               pr_warning("Could not create debugfs 'failures' entry\n");
+
        entry = debugfs_create_file("set_ftrace_filter", 0644, d_tracer,
                                    NULL, &ftrace_filter_fops);
        if (!entry)