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: stable@vger.kernel.org
Fixes: 8c08f0d5c6fb ("ftrace: Have cached module filters be an active filter")
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
---
 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

On Mon, 26 Sep 2022 15:20:08 +0000
Zheng Yejian <zhengyejian1@huawei.com> 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: stable@vger.kernel.org
> Fixes: 8c08f0d5c6fb ("ftrace: Have cached module filters be an active filter")
> Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>

Thanks, this definitely looks like a bug.

I'll be reviewing these patches later this week.

-- Steve