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Commit 694ce0a5 authored by Li Zefan's avatar Li Zefan Committed by Ingo Molnar
Browse files

ftrace: Don't manipulate @pos in t_start() 



It's rather confusing that in t_start(), in some cases @pos is
incremented, and in some cases it's decremented and then incremented.

This patch rewrites t_start() in a much more general way.

Thus we fix a bug that if ftrace_filtered == 1, functions have tracer
hooks won't be printed, because the branch is always unreachable:

static void *t_start(...)
{
	...
	if (!p)
		return t_hash_start(m, pos);
	return p;
}

Before:
  # echo 'sys_open' > /mnt/tracing/set_ftrace_filter
  # echo 'sys_write:traceon:4' >> /mnt/tracing/set_ftrace_filter
  sys_open

After:
  # echo 'sys_open' > /mnt/tracing/set_ftrace_filter
  # echo 'sys_write:traceon:4' >> /mnt/tracing/set_ftrace_filter
  sys_open
  sys_write:traceon:count=4

Reviewed-by: default avatarLiming Wang <liming.wang@windriver.com>
Signed-off-by: default avatarLi Zefan <lizf@cn.fujitsu.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <4A41874B.4090507@cn.fujitsu.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 85951842

kernel/trace/ftrace.c

+8 −11
Original line number Original line Diff line number Diff line
@@ -1467,8 +1467,6 @@ t_next(struct seq_file *m, void *v, loff_t *pos) 
			iter->pg = iter->pg->next;

			iter->pg = iter->pg->next;

			iter->idx = 0;

			iter->idx = 0;

			goto retry;

			goto retry;

		} else {

			iter->idx = -1;

		}

		}

	} else {

	} else {

		rec = &iter->pg->records[iter->idx++];

		rec = &iter->pg->records[iter->idx++];
@@ -1497,6 +1495,7 @@ static void *t_start(struct seq_file *m, loff_t *pos) 
{

{

	struct ftrace_iterator *iter = m->private;

	struct ftrace_iterator *iter = m->private;

	void *p = NULL;

	void *p = NULL;

	loff_t l;





	mutex_lock(&ftrace_lock);

	mutex_lock(&ftrace_lock);

	/*

	/*
@@ -1508,23 +1507,21 @@ static void *t_start(struct seq_file *m, loff_t *pos) 
		if (*pos > 0)

		if (*pos > 0)

			return t_hash_start(m, pos);

			return t_hash_start(m, pos);

		iter->flags |= FTRACE_ITER_PRINTALL;

		iter->flags |= FTRACE_ITER_PRINTALL;

		(*pos)++;

		return iter;

		return iter;

	}

	}





	if (iter->flags & FTRACE_ITER_HASH)

	if (iter->flags & FTRACE_ITER_HASH)

		return t_hash_start(m, pos);

		return t_hash_start(m, pos);





	if (*pos > 0) {

	iter->pg = ftrace_pages_start;

		if (iter->idx < 0)

	iter->idx = 0;

			return p;

	for (l = 0; l <= *pos; ) {

		(*pos)--;

		p = t_next(m, p, &l);

		iter->idx--;

		if (!p)

			break;

	}

	}





	p = t_next(m, p, pos);

	if (!p && iter->flags & FTRACE_ITER_FILTER)



	if (!p)

		return t_hash_start(m, pos);

		return t_hash_start(m, pos);





	return p;

	return p;