Re: [PATCH] tracing/kprobes: Check whether get_kretprobe() returns NULL in kretprobe_dispatcher()

[Song Liu <songliubraving@fb.com>]

> On May 27, 2022, at 8:55 AM, Masami Hiramatsu (Google) <mhiramat@kernel.org> 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>

Acked-by: Song Liu <song@kernel.org>

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