linux-kernel - Re: lockdep trace from posix timers

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Message-ID: <1345463458.23018.37.camel@twins>
Date:	Mon, 20 Aug 2012 13:50:58 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Oleg Nesterov <oleg@...hat.com>
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 Mon, 2012-08-20 at 13:44 +0200, Peter Zijlstra wrote:
>  int
> +task_work_add(struct task_struct *task, struct callback_head *work, bool notify)
>  {
> +       struct callback_head **head = &task->task_works;
> +       struct callback_head *entry, *old_entry;
> +
> +       entry = &head;

My compiler just alerted me that: 

	entry = *head; 

works a lot better..

> +       for (;;) {
> +               if (entry == &dead)
> +                       return -ESRCH;
> +
> +               old_entry = entry;
> +               work->next = entry;
> +               entry = cmpxchg(head, old_entry, work);
> +               if (entry == old_entry)
> +                       break;
> +       }
>  
>         /* test_and_set_bit() implies mb(), see tracehook_notify_resume(). */
>         if (notify)
>                 set_notify_resume(task);
> +
>         return 0;
>  } 
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