[tip:tracing/urgent] ftrace: Don't manipulate @pos in t_start()

tip-bot for Li Zefan
2009-06-24T09:47:40Z

Commit-ID: 694ce0a544fba37a60025a6803ee6265be8a2a22
Gitweb: http://git.kernel.org/tip/694ce0a544fba37a60025a6803ee6265be8a2a22
Author: Li Zefan <lizf@cn.fujitsu.com>
AuthorDate: Wed, 24 Jun 2009 09:54:19 +0800
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 24 Jun 2009 11:02:53 +0200

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: 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: <4A41874B.4090507@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

---
kernel/trace/ftrace.c | 19 ++++++++-----------
1 files changed, 8 insertions(+), 11 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index cde74b9..dc81020 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1467,8 +1467,6 @@ t_next(struct seq_file *m, void *v, loff_t *pos)
iter->pg = iter->pg->next;
iter->idx = 0;
goto retry;
- } else {
- iter->idx = -1;
}
} else {
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;
void *p = NULL;
+ loff_t l;

mutex_lock(&ftrace_lock);
/*
@@ -1508,23 +1507,21 @@ static void *t_start(struct seq_file *m, loff_t *pos)
if (*pos > 0)
return t_hash_start(m, pos);
iter->flags |= FTRACE_ITER_PRINTALL;
- (*pos)++;
return iter;
}

if (iter->flags & FTRACE_ITER_HASH)
return t_hash_start(m, pos);

- if (*pos > 0) {
- if (iter->idx < 0)
- return p;
- (*pos)--;
- iter->idx--;
+ iter->pg = ftrace_pages_start;
+ iter->idx = 0;
+ for (l = 0; l <= *pos; ) {
+ p = t_next(m, p, &l);
+ if (!p)
+ break;
}

- p = t_next(m, p, pos);
-
- if (!p)
+ if (!p && iter->flags & FTRACE_ITER_FILTER)
return t_hash_start(m, pos);

return p;