2022-09-26 08:21:29

by Zheng Yejian

Subject: [PATCH] ftrace: Properly unset FTRACE_HASH_FL_MOD

When executing following commands like what document said, but the log
"#### all functions enabled ####" was not shown as expect:
1. Set a 'mod' filter:
$ echo 'write*:mod:ext3' > /sys/kernel/tracing/set_ftrace_filter
2. Invert above filter:
$ echo '!write*:mod:ext3' >> /sys/kernel/tracing/set_ftrace_filter
3. Read the file:
$ cat /sys/kernel/tracing/set_ftrace_filter

By some debugging, I found that flag FTRACE_HASH_FL_MOD was not unset
after inversion like above step 2 and then result of ftrace_hash_empty()
is incorrect.

Cc: [email protected]
Fixes: 8c08f0d5c6fb ("ftrace: Have cached module filters be an active filter")
Signed-off-by: Zheng Yejian <[email protected]>
---
kernel/trace/ftrace.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 439e2ab6905e..5a1ec7e1af33 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6081,8 +6081,12 @@ int ftrace_regex_release(struct inode *inode, struct file *file)

if (filter_hash) {
orig_hash = &iter->ops->func_hash->filter_hash;
- if (iter->tr && !list_empty(&iter->tr->mod_trace))
- iter->hash->flags |= FTRACE_HASH_FL_MOD;
+ if (iter->tr) {
+ if (list_empty(&iter->tr->mod_trace))
+ iter->hash->flags &= ~FTRACE_HASH_FL_MOD;
+ else
+ iter->hash->flags |= FTRACE_HASH_FL_MOD;
+ }
} else
orig_hash = &iter->ops->func_hash->notrace_hash;

--
2.25.1

2022-09-26 16:41:07

by Steven Rostedt

Subject: Re: [PATCH] ftrace: Properly unset FTRACE_HASH_FL_MOD

On Mon, 26 Sep 2022 15:20:08 +0000
Zheng Yejian <[email protected]> wrote:

> When executing following commands like what document said, but the log
> "#### all functions enabled ####" was not shown as expect:
> 1. Set a 'mod' filter:
> $ echo 'write*:mod:ext3' > /sys/kernel/tracing/set_ftrace_filter
> 2. Invert above filter:
> $ echo '!write*:mod:ext3' >> /sys/kernel/tracing/set_ftrace_filter
> 3. Read the file:
> $ cat /sys/kernel/tracing/set_ftrace_filter
>
> By some debugging, I found that flag FTRACE_HASH_FL_MOD was not unset
> after inversion like above step 2 and then result of ftrace_hash_empty()
> is incorrect.
>
> Cc: [email protected]
> Fixes: 8c08f0d5c6fb ("ftrace: Have cached module filters be an active filter")
> Signed-off-by: Zheng Yejian <[email protected]>

Thanks, this definitely looks like a bug.

I'll be reviewing these patches later this week.

-- Steve