ftrace: Fix indexing of t_hash_start() from t_next()

t_hash_start() does not increment *pos, where as t_next() must. But when
t_next() does increment *pos, it must still pass in the original *pos to
t_hash_start() otherwise it will skip the first instance:

 # cd /sys/kernel/debug/tracing
 # echo schedule:traceoff > set_ftrace_filter
 # echo do_IRQ:traceoff > set_ftrace_filter
 # echo call_rcu > set_ftrace_filter
 # cat set_ftrace_filter
call_rcu
schedule:traceoff:unlimited
do_IRQ:traceoff:unlimited

The above called t_hash_start() from t_start() as there was only one
function (call_rcu), but if we add another function:

 # echo xfrm_policy_destroy_rcu >> set_ftrace_filter
 # cat set_ftrace_filter
call_rcu
xfrm_policy_destroy_rcu
do_IRQ:traceoff:unlimited

The "schedule:traceoff" disappears.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 4b6459a57fbc5f92f591be1c831f910373687c82..b21a3e61ac743ca0ccd794eb67ba1142808b3b8c 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3205,6 +3205,7 @@ static void *
 t_next(struct seq_file *m, void *v, loff_t *pos)
 {
        struct ftrace_iterator *iter = m->private;
+       loff_t l = *pos; /* t_hash_start() must use original pos */
        void *ret;
 
        if (unlikely(ftrace_disabled))
@@ -3216,13 +3217,13 @@ t_next(struct seq_file *m, void *v, loff_t *pos)
        if (iter->flags & FTRACE_ITER_PRINTALL) {
                /* next must increment pos, and t_hash_start does not */
                (*pos)++;
-               return t_hash_start(m, pos);
+               return t_hash_start(m, &l);
        }
 
        ret = t_func_next(m, pos);
 
        if (!ret)
-               return t_hash_start(m, pos);
+               return t_hash_start(m, &l);
 
        return ret;
 }