linux-kernel - Re: [PATCH] trace: reenable preemption if we modify the ip

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Date:   Mon, 18 Dec 2017 16:29:47 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Josef Bacik <josef@...icpanda.com>
Cc:     netdev@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        darrick.wong@...cle.com, linux-kernel@...r.kernel.org,
        Josef Bacik <jbacik@...com>
Subject: Re: [PATCH] trace: reenable preemption if we modify the ip

On Fri, 15 Dec 2017 21:42:57 -0500
Josef Bacik <josef@...icpanda.com> wrote:

> From: Josef Bacik <jbacik@...com>
> 
> Things got moved around between the original bpf_override_return patches
> and the final version, and now the ftrace kprobe dispatcher assumes if
> you modified the ip that you also enabled preemption.  Make a comment of
> this and enable preemption, this fixes the lockdep splat that happened
> when using this feature.
> 
> Signed-off-by: Josef Bacik <jbacik@...com>
> ---
>  kernel/trace/trace_kprobe.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 5db849809a56..91f4b57dab82 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -1322,8 +1322,15 @@ static int kprobe_dispatcher(struct kprobe *kp, struct pt_regs *regs)
>  	if (tk->tp.flags & TP_FLAG_TRACE)
>  		kprobe_trace_func(tk, regs);
>  #ifdef CONFIG_PERF_EVENTS
> -	if (tk->tp.flags & TP_FLAG_PROFILE)
> +	if (tk->tp.flags & TP_FLAG_PROFILE) {
>  		ret = kprobe_perf_func(tk, regs);
> +		/*
> +		 * The ftrace kprobe handler leaves it up to us to re-enable
> +		 * preemption here before returning if we've modified the ip.
> +		 */
> +		if (ret)
> +			preempt_enable_no_resched();

Where is reset_current_kprobe()?
Since kprobes still expects this modification is used by jprobes,
we need to call it in caller-side.

Thank you,

> +	}
>  #endif
>  	return ret;
>  }
> -- 
> 2.7.5
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>