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

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Message-ID: <20161024122748.GO3102@twins.programming.kicks-ass.net>
Date:   Mon, 24 Oct 2016 14:27:48 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Oleg Nesterov <oleg@...hat.com>
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 Mon, Oct 24, 2016 at 02:21:23PM +0200, Oleg Nesterov wrote:
> > Should we do the same for perf_event_tid() and report -1 as the pid/tid
> > in the !alive case? -1 should be an obvious invalid pid since we limit
> > the pid-space to less than 32 bits.
> 
> task_pid_nr_ns() is always safe, it calls __task_pid_nr_ns(). But yes,
> it can return zero if called after exit_notify() and/or release_task().
> 
> And while zero is not a valid pid too, I guess it can be confused with
> the idle thread's "pid" ?

Right, 0 is the idle thread.