Commit fcdc7125 authored Apr 17, 2017 by Steven Rostedt (VMware)

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>

parent acceb72e

kernel/trace/ftrace.c

+3 −2

Original line number	Diff line number	Diff line
		@@ -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;
		}