linux-kernel - Re: lockdep trace from posix timers

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Message-ID: <20120820145919.GB18499@redhat.com>
Date:	Mon, 20 Aug 2012 16:59:19 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	rostedt <rostedt@...dmis.org>, dhowells <dhowells@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: lockdep trace from posix timers

On 08/20, Peter Zijlstra wrote:
>
>  task_work_cancel(struct task_struct *task, task_work_func_t func)
>  {
> ...
> +
> +again:
> +	workp = &task->task_works;
> +	work = *workp;
> +	while (work) {
> +		if (work->func == func) {

But this all can race with task_work_run() if task != current.

This "work" can be freed/reused. And it should only return !NULL
if twork->func() was not called.

Oleg.

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