Re: [PATCH v2] tracepoint: Do not fail unregistering a probe due to memory allocation

[Steven Rostedt <rostedt@goodmis.org>]

On Wed, 27 Jan 2021 18:08:34 +1100
Alexey Kardashevskiy <aik@ozlabs.ru> wrote:

> 
> I am running syzkaller and the kernel keeps crashing in 
> __traceiter_##_name. This patch makes these crashes happen lot less 

I have another solution to the above issue. But I'm now concerned with what
you write below.

> often (and so did the v1) but the kernel still crashes (examples below 
> but the common thing is that they crash in tracepoints). Disasm points 
> to __DO_TRACE_CALL(name) and this fixes it:
> 
> ========================
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -313,6 +313,7 @@ static inline struct tracepoint 
> *tracepoint_ptr_deref(tracepoint_ptr_t *p)
>                                                                          \
>                  it_func_ptr =                                           \
>  
> rcu_dereference_raw((&__tracepoint_##_name)->funcs); \
> +               if (it_func_ptr)                                        \

Looking at v2 of the patch, I found a bug that could make this happen.

I'm looking at doing something else that doesn't affect the fast path nor
does it bloat the kernel more than necessary.

I'll see if I can get that patch out today.

Thanks for the report.

-- Steve