From: Alan Stern <stern@rowland.harvard.edu>
To: Oleg Nesterov <oleg@tv-sign.ru>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>,
Kernel development list <linux-kernel@vger.kernel.org>
Subject: Re: [patch] cpufreq: mark cpufreq_tsc() as core_initcall_sync
Date: Mon, 27 Nov 2006 16:10:27 -0500 (EST) [thread overview]
Message-ID: <Pine.LNX.4.44L0.0611271608470.2786-100000@iolanthe.rowland.org> (raw)
In-Reply-To: <20061126222547.GB110@oleg>
On Mon, 27 Nov 2006, Oleg Nesterov wrote:
> I still can't relax, another attempt to "prove" this should not be
> possible on CPUs supported by Linux :)
>
> Let's suppose it is possible, then it should also be possible if CPU_1
> does spin_lock() instead of mb() (spin_lock can't be "stronger"), yes?
>
> Now,
>
> int COND;
> wait_queue_head_t wq;
>
> my_wait()
> {
> add_wait_queue(&wq);
> for (;;) {
> set_current_state(TASK_UNINTERRUPTIBLE);
>
> if (COND)
> break;
>
> schedule();
> }
> remove_wait_queue(&wq);
> }
>
> my_wake()
> {
> COND = 1;
> wake_up(&wq);
> }
>
> this should be correct, but it is not!
>
> my_wait:
>
> task->state = TASK_UNINTERRUPTIBLE; // STORE
>
> mb();
>
> if (COND) break; // LOAD
>
>
> my_wake:
>
> COND = 1; // STORE
>
> spin_lock(WQ.lock);
> spin_lock(runqueue.lock);
>
> // try_to_wake_up()
> if (!(task->state & TASK_UNINTERRUPTIBLE)) // LOAD
> goto out;
>
>
> So, my_wait() gets COND == 0, and goes to schedule in 'D' state.
> try_to_wake_up() reads ->state == TASK_RUNNING, and does nothing.
This is a very good point. I don't know what the resolution is; Paul will
have to explain the situation.
Alan
next prev parent reply other threads:[~2006-11-27 21:10 UTC|newest]
Thread overview: 108+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-11-16 20:00 BUG: cpufreq notification broken Thomas Gleixner
2006-11-16 20:15 ` [patch] cpufreq: mark cpufreq_tsc() as core_initcall_sync Ingo Molnar
2006-11-16 20:45 ` Thomas Gleixner
2006-11-16 21:47 ` Linus Torvalds
2006-11-16 22:03 ` Alan Stern
2006-11-16 22:21 ` Linus Torvalds
2006-11-17 3:06 ` Alan Stern
2006-11-17 6:51 ` Paul E. McKenney
2006-11-17 9:29 ` Jens Axboe
2006-11-17 18:39 ` Oleg Nesterov
2006-11-18 0:28 ` Paul E. McKenney
2006-11-18 16:15 ` Alan Stern
2006-11-18 17:14 ` Paul E. McKenney
2006-11-18 19:34 ` Oleg Nesterov
2006-11-19 21:26 ` Paul E. McKenney
2006-11-18 21:00 ` Alan Stern
2006-11-18 21:25 ` Oleg Nesterov
2006-11-18 22:13 ` Alan Stern
2006-11-18 22:46 ` Oleg Nesterov
2006-11-19 20:12 ` Alan Stern
2006-11-19 21:43 ` Paul E. McKenney
2006-11-20 17:19 ` Alan Stern
2006-11-20 17:58 ` Jens Axboe
2006-11-20 19:39 ` Alan Stern
2006-11-20 20:13 ` Jens Axboe
2006-11-20 21:39 ` Alan Stern
2006-11-21 7:39 ` Jens Axboe
2006-11-20 18:57 ` Oleg Nesterov
2006-11-20 20:01 ` Alan Stern
2006-11-20 20:51 ` Paul E. McKenney
2006-11-21 20:04 ` Oleg Nesterov
2006-11-21 20:54 ` Alan Stern
2006-11-21 22:07 ` Paul E. McKenney
2006-11-20 20:38 ` Paul E. McKenney
2006-11-21 16:44 ` Oleg Nesterov
2006-11-21 19:56 ` Paul E. McKenney
2006-11-21 20:26 ` Alan Stern
2006-11-21 23:03 ` Paul E. McKenney
2006-11-22 2:17 ` Alan Stern
2006-11-22 17:01 ` Paul E. McKenney
2006-11-26 22:25 ` Oleg Nesterov
2006-11-27 21:10 ` Alan Stern [this message]
2006-11-28 1:47 ` Paul E. McKenney
2006-11-20 19:17 ` Paul E. McKenney
2006-11-20 20:22 ` Alan Stern
2006-11-21 17:55 ` Paul E. McKenney
2006-11-21 17:56 ` Alan Stern
2006-11-21 19:13 ` Paul E. McKenney
2006-11-21 20:40 ` Alan Stern
2006-11-22 18:08 ` Paul E. McKenney
2006-11-21 21:01 ` Oleg Nesterov
2006-11-22 0:51 ` Paul E. McKenney
2006-11-18 18:46 ` Oleg Nesterov
2006-11-19 21:07 ` Paul E. McKenney
2006-11-20 7:15 ` Jens Axboe
2006-11-20 16:59 ` Paul E. McKenney
2006-11-20 17:55 ` Jens Axboe
2006-11-20 20:09 ` Paul E. McKenney
2006-11-20 20:21 ` Jens Axboe
2006-11-18 19:02 ` Oleg Nesterov
2006-11-19 21:23 ` Paul E. McKenney
2006-11-17 19:15 ` Paul E. McKenney
2006-11-17 19:27 ` Alan Stern
2006-11-18 0:38 ` Paul E. McKenney
2006-11-18 4:33 ` Alan Stern
2006-11-18 4:51 ` Andrew Morton
2006-11-18 5:57 ` Paul E. McKenney
2006-11-19 19:00 ` Oleg Nesterov
2006-11-19 20:21 ` Alan Stern
2006-11-19 20:55 ` Oleg Nesterov
2006-11-19 21:09 ` Alan Stern
2006-11-19 21:17 ` Oleg Nesterov
2006-11-19 21:54 ` Paul E. McKenney
2006-11-19 22:28 ` Oleg Nesterov
2006-11-20 5:47 ` Paul E. McKenney
2006-11-19 21:20 ` Paul E. McKenney
2006-11-19 21:50 ` Oleg Nesterov
2006-11-19 22:04 ` Paul E. McKenney
2006-11-23 14:59 ` Oleg Nesterov
2006-11-23 20:40 ` Paul E. McKenney
2006-11-23 21:34 ` Oleg Nesterov
2006-11-23 21:49 ` Oleg Nesterov
2006-11-27 4:33 ` Paul E. McKenney
2006-11-24 18:21 ` Oleg Nesterov
2006-11-24 20:04 ` Jens Axboe
2006-11-24 20:47 ` Alan Stern
2006-11-24 21:13 ` Oleg Nesterov
2006-11-25 3:24 ` Alan Stern
2006-11-25 17:14 ` Oleg Nesterov
2006-11-25 22:06 ` Alan Stern
2006-11-26 21:34 ` Oleg Nesterov
2006-11-27 5:02 ` Paul E. McKenney
2006-11-27 16:11 ` Oleg Nesterov
2006-11-27 16:56 ` Oleg Nesterov
2006-11-29 19:29 ` Paul E. McKenney
2006-11-29 20:16 ` Oleg Nesterov
2006-11-29 23:08 ` Paul E. McKenney
2006-11-30 0:01 ` Oleg Nesterov
2006-11-17 2:33 ` Paul E. McKenney
2006-11-16 20:52 ` Peter Zijlstra
2006-11-16 21:20 ` Andrew Morton
2006-11-16 21:27 ` Thomas Gleixner
2006-11-20 19:57 ` Linus Torvalds
2006-11-16 20:27 ` BUG: cpufreq notification broken Alan Stern
2006-11-16 21:09 ` Thomas Gleixner
2006-11-16 21:26 ` Alan Stern
2006-11-16 21:36 ` Thomas Gleixner
2006-11-16 21:56 ` Alan Stern
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