tracing: fix memory leak in trace_stat

If the function profiler does not have any items recorded and one were
to cat the function stat file, the kernel would take a BUG with a NULL
pointer dereference.

Looking further into this, I found that returning NULL from stat_start
did not stop the stat logic, and would later call stat_next. This breaks
from the way seq_file works, so I looked into fixing the stat code.

This is where I noticed that the last next_entry is never freed.
It is allocated, and if the stat_next returns NULL, the code breaks out
of the loop, unlocks the mutex and exits. We never link the next_entry
nor do we free it. Thus it is a real memory leak.

This patch rearranges the code a bit to not only fix the memory leak,
but also to act more like seq_file where nothing is printed if there
is nothing to print. That is, stat_start returns NULL.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

diff --git a/kernel/trace/trace_stat.c b/kernel/trace/trace_stat.c
index 39310e3..f71b85b 100644 (file)
--- a/kernel/trace/trace_stat.c
+++ b/kernel/trace/trace_stat.c
@@ -75,7 +75,7 @@ static int stat_seq_init(struct tracer_stat_session *session)
 {
        struct trace_stat_list *iter_entry, *new_entry;
        struct tracer_stat *ts = session->ts;
-       void *prev_stat;
+       void *stat;
        int ret = 0;
        int i;
 
@@ -85,6 +85,10 @@ static int stat_seq_init(struct tracer_stat_session *session)
        if (!ts->stat_cmp)
                ts->stat_cmp = dummy_cmp;
 
+       stat = ts->stat_start();
+       if (!stat)
+               goto exit;
+
        /*
         * The first entry. Actually this is the second, but the first
         * one (the stat_list head) is pointless.
@@ -99,14 +103,19 @@ static int stat_seq_init(struct tracer_stat_session *session)
 
        list_add(&new_entry->list, &session->stat_list);
 
-       new_entry->stat = ts->stat_start();
-       prev_stat = new_entry->stat;
+       new_entry->stat = stat;
 
        /*
         * Iterate over the tracer stat entries and store them in a sorted
         * list.
         */
        for (i = 1; ; i++) {
+               stat = ts->stat_next(stat, i);
+
+               /* End of insertion */
+               if (!stat)
+                       break;
+
                new_entry = kmalloc(sizeof(struct trace_stat_list), GFP_KERNEL);
                if (!new_entry) {
                        ret = -ENOMEM;
@@ -114,11 +123,7 @@ static int stat_seq_init(struct tracer_stat_session *session)
                }
 
                INIT_LIST_HEAD(&new_entry->list);
-               new_entry->stat = ts->stat_next(prev_stat, i);
-
-               /* End of insertion */
-               if (!new_entry->stat)
-                       break;
+               new_entry->stat = stat;
 
                list_for_each_entry(iter_entry, &session->stat_list, list) {
 
@@ -137,8 +142,6 @@ static int stat_seq_init(struct tracer_stat_session *session)
                                break;
                        }
                }
-
-               prev_stat = new_entry->stat;
        }
 exit:
        mutex_unlock(&session->stat_mutex);