From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1755507AbdCGOAH (ORCPT <rfc822;w@1wt.eu>);
        Tue, 7 Mar 2017 09:00:07 -0500
Received: from bombadil.infradead.org ([65.50.211.133]:58012 "EHLO
        bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1755208AbdCGN76 (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 7 Mar 2017 08:59:58 -0500
Date: Tue, 7 Mar 2017 14:27:41 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        syzkaller <syzkaller@googlegroups.com>,
        Oleg Nesterov <oleg@redhat.com>
Subject: Re: perf: use-after-free in perf_release
Message-ID: <20170307132741.GB3358@twins.programming.kicks-ass.net>
References: <CACT4Y+bgMfF=jUjNcVSSrBZy0xbyCPeNiDsW-c-S9sHe-Vxc=g@mail.gmail.com>
 <20170306131459.GC6515@twins.programming.kicks-ass.net>
 <20170307131649.GA3358@twins.programming.kicks-ass.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20170307131649.GA3358@twins.programming.kicks-ass.net>
User-Agent: Mutt/1.5.23.1 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Mar 07, 2017 at 02:16:49PM +0100, Peter Zijlstra wrote:
> So I _think_ find_task_by_vpid() can return an already dead task; and
> we'll happily increase task->usage.

Hurm, so find_get_context() already does the PF_EXITING test. And then
the put_ctx would've been from find_get_context(), not fput().

So still puzzled.