linux-kernel - Re: hit a KASan bug related to Perf during stress test

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Message-ID: <20161024134012.GA20798@redhat.com>
Date:   Mon, 24 Oct 2016 15:40:13 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Ni, BaoleX" <baolex.ni@...el.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "acme@...nel.org" <acme@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "Liu, Chuansheng" <chuansheng.liu@...el.com>
Subject: Re: hit a KASan bug related to Perf during stress test

On 10/24, Oleg Nesterov wrote:
>
> -static u32 perf_event_pid(struct perf_event *event, struct task_struct *p)
> +static u32 perf_event_xxx(struct perf_event *event, struct task_struct *p,
> +			 	enum pid_type type)
>  {
> +	pid_t nr;
>  	/*
>  	 * only top level events have the pid namespace they were created in
>  	 */
>  	if (event->parent)
>  		event = event->parent;
>
> -	return task_tgid_nr_ns(p, event->ns);
> +	nr = __task_pid_nr_ns(p, type, event->ns);
> +	if (!nr && !is_idle_task(p))
> +		nr = -1;
> +	return nr;

And just in case... In any case __task_pid_nr_ns() and other similar helpers
can also return zero if "p" runs in another namespace. Say, in the parent ns.

Say, perf_event_switch_output(). What do we want to report in this case, zero
or -1 ?

Oleg.