ftrace: Fix t_hash_start()

When the output of set_ftrace_filter is larger than PAGE_SIZE,
t_hash_start() will be called the 2nd time, and then we start
from the head of a hlist, which is wrong and causes some entries
to be outputed twice.

The worse is, if the hlist is large enough, reading set_ftrace_filter
won't stop but in a dead loop.

Reviewed-by: Liming Wang <liming.wang@windriver.com>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <4A41876E.2060407@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index dc81020..71a52c1 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1417,10 +1417,20 @@ static void *t_hash_start(struct seq_file *m, loff_t *pos)
 {
        struct ftrace_iterator *iter = m->private;
        void *p = NULL;
+       loff_t l;
+
+       if (!(iter->flags & FTRACE_ITER_HASH))
+               *pos = 0;
 
        iter->flags |= FTRACE_ITER_HASH;
 
-       return t_hash_next(m, p, pos);
+       iter->hidx = 0;
+       for (l = 0; l <= *pos; ) {
+               p = t_hash_next(m, p, &l);
+               if (!p)
+                       break;
+       }
+       return p;
 }
 
 static int t_hash_show(struct seq_file *m, void *v)