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Date:   Wed, 27 Jan 2021 09:30:48 -0500
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Alexey Kardashevskiy <aik@ozlabs.ru>
Cc:     Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Matt Mullins <mmullins@mmlx.us>, paulmck <paulmck@kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Dmitry Vyukov <dvyukov@google.com>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        Andrii Nakryiko <andriin@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@chromium.org>,
        netdev <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [PATCH v2] tracepoint: Do not fail unregistering a probe due to
 memory allocation
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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