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Subject: Re: [PATCH] tracing/kprobes: Check whether get_kretprobe() returns
 NULL in kretprobe_dispatcher()
To:     Steven Rostedt <rostedt@goodmis.org>,
        "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>, Yonghong Song <yhs@fb.com>,
        bpf <bpf@vger.kernel.org>, Kernel Team <kernel-team@fb.com>,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org
References: <165366693881.797669.16926184644089588731.stgit@devnote2>
 <0204f480-cdb0-e49f-9034-602eced02966@iogearbox.net>
 <7619DB57-C39B-4A49-808C-7ACF12D58592@goodmis.org>
From:   Daniel Borkmann <daniel@iogearbox.net>
Message-ID: <d28e1548-98fb-a533-4fdc-ae4f4568fb75@iogearbox.net>
Date:   Wed, 8 Jun 2022 14:38:39 +0200
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On 5/31/22 12:00 AM, Steven Rostedt wrote:
> On May 30, 2022 9:33:23 PM GMT+02:00, Daniel Borkmann <daniel@iogearbox.net> wrote:
>> On 5/27/22 5:55 PM, Masami Hiramatsu (Google) wrote:
>>> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
>>>
>>> There is a small chance that get_kretprobe(ri) returns NULL in
>>> kretprobe_dispatcher() when another CPU unregisters the kretprobe
>>> right after __kretprobe_trampoline_handler().
>>>
>>> To avoid this issue, kretprobe_dispatcher() checks the get_kretprobe()
>>> return value again. And if it is NULL, it returns soon because that
>>> kretprobe is under unregistering process.
>>>
>>> This issue has been introduced when the kretprobe is decoupled
>>> from the struct kretprobe_instance by commit d741bf41d7c7
>>> ("kprobes: Remove kretprobe hash"). Before that commit, the
>>> struct kretprob_instance::rp directly points the kretprobe
>>> and it is never be NULL.
>>>
>>> Reported-by: Yonghong Song <yhs@fb.com>
>>> Fixes: d741bf41d7c7 ("kprobes: Remove kretprobe hash")
>>> Cc: stable@vger.kernel.org
>>> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
>>
>> Steven, I presume you'll pick this fix up?
> 
> I'm currently at Embedded/Kernel Recipes, but yeah, I'll take a look at it. (Just need to finish my slides first ;-)

Ok, thanks. If I don't hear back I presume you'll pick it up then.