2021-11-09 23:30:48

by Jiri Olsa

Subject: [PATCH] ftrace/direct: Fix lockup in modify_ftrace_direct_multi

We can't call unregister_ftrace_function under ftrace_lock.

Fixes: ed29271894aa ("ftrace/direct: Do not disable when switching direct callers")
Signed-off-by: Jiri Olsa <[email protected]>
---
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;
--
2.32.0

2021-11-10 00:05:16

by Steven Rostedt

Subject: Re: [PATCH] ftrace/direct: Fix lockup in modify_ftrace_direct_multi

On Tue, 9 Nov 2021 12:42:17 +0100
Jiri Olsa <[email protected]> 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 <[email protected]>
> ---
> 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;

2021-11-10 00:11:42

by Jiri Olsa

Subject: Re: [PATCH] ftrace/direct: Fix lockup in modify_ftrace_direct_multi

On Tue, Nov 09, 2021 at 11:02:37AM -0500, Steven Rostedt wrote:
> On Tue, 9 Nov 2021 12:42:17 +0100
> Jiri Olsa <[email protected]> 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.

I triggered that with my bpf batch changes

there's not test for modify at the moment,
just register/unregister I'll add one

jirka

>
> -- Steve
>
> >
> > Fixes: ed29271894aa ("ftrace/direct: Do not disable when switching direct callers")
> > Signed-off-by: Jiri Olsa <[email protected]>
> > ---
> > 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;
>