linux-kernel - Re: [PATCH v2 15/15] kprobes: Free kretprobe

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Message-ID: <20200827114807.GA2674@hirez.programming.kicks-ass.net>
Date:   Thu, 27 Aug 2020 13:48:07 +0200
From:   peterz@...radead.org
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Eddy Wu <Eddy_Wu@...ndmicro.com>,
        x86@...nel.org, "David S . Miller" <davem@...emloft.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        linux-arch@...r.kernel.org
Subject: Re: [PATCH v2 15/15] kprobes: Free kretprobe_instance with rcu
 callback

On Thu, Aug 27, 2020 at 08:37:49PM +0900, Masami Hiramatsu wrote:
> Free kretprobe_instance with rcu callback instead of directly
> freeing the object in the kretprobe handler context.
> 
> This will make kretprobe run safer in NMI context.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---
>  include/linux/kprobes.h |    3 ++-
>  kernel/kprobes.c        |   25 ++++++-------------------
>  2 files changed, 8 insertions(+), 20 deletions(-)
> 
> diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> index 46a7afcf5ec0..97557f820d9b 100644
> --- a/include/linux/kprobes.h
> +++ b/include/linux/kprobes.h
> @@ -160,6 +160,7 @@ struct kretprobe_instance {
>  	struct kretprobe *rp;
>  	kprobe_opcode_t *ret_addr;
>  	struct task_struct *task;
> +	struct rcu_head rcu;
>  	void *fp;
>  	char data[];
>  };

You can stick the rcu_head in a union with hlist.