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SubjectRe: [PATCH] ftrace/direct: Fix lockup in modify_ftrace_direct_multi
On Tue,  9 Nov 2021 12:42:17 +0100
Jiri Olsa <jolsa@redhat.com> wrote:

> We can't call unregister_ftrace_function under ftrace_lock.

Ouch.

Do you have a sample module that triggers this?

I thought we had something that tested this code, but I don't see it in my
tree.

-- Steve

>
> Fixes: ed29271894aa ("ftrace/direct: Do not disable when switching direct callers")
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
> kernel/trace/ftrace.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index b4ed1a301232..fc49e8809a56 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -5602,10 +5602,11 @@ int modify_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr)
> }
> }
>
> + mutex_unlock(&ftrace_lock);
> +
> /* Removing the tmp_ops will add the updated direct callers to the functions */
> unregister_ftrace_function(&tmp_ops);
>
> - mutex_unlock(&ftrace_lock);
> out_direct:
> mutex_unlock(&direct_mutex);
> return err;

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